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Research Paper
A first syntaxonomic description of the vegetation of the Karstveld in Namibia
expand article infoBen J. Strohbach§, Marianne M. Strohbach|
‡ National Botanical Research Institute, Ministry of Agriculture, Water and Forestry, Windhoek, Namibia
§ Namibia University of Science and Technology, Windhoek, Namibia
| Unaffiliated, Johannesburg, South Africa
Open Access

Abstract

Aims: The Karstveld in Namibia has been recognized as an area of high plant diversity. However, this area is also recognised as a hotspot of various forms of degradation including bush encroachment. Minimal baseline data on the composition and diversity of vegetation in this area is available, therefore this paper is a first attempt to rectify this data deficiency. Study area: The Karstveld in Namibia is formed around the Otavi Mountain Range in northern Central Namibia, consisting of strongly karstified carbonate bedrock, rising up to 2000 m a.s.l. The Karstveld includes the Ovambo Basin plains with shallow calcrete soils north of the range, up to the Omuramba Ovambo. Because of orographic effects, the area receives some of the highest rainfall in Namibia, with up to 600 mm per year. Methods: A set of 889 relevés with 868 species was selected from the GVID ID AF-NA-001 database. A partial data set, using trees, shrubs, dwarf shrubs and grasses only, was used for the classification with modified TWINSPAN. The initial result yielded four main groups, according to which the data was split and further classified. Several vegetation types observed during field surveys were not reflected in the classification results; these were refined using Cocktail with known characteristic species. Results: The four main units represented wetlands and grasslands with six associations, a Thornbush savanna – Karstveld transition zone with four associations, Kalahari vegetation with four associations and the Karstveld proper with eight associations. The latter are grouped together as the Terminalietea prunioides, with two orders and three alliances recognised under them. We describe 16 associations according to the ICPN. Conclusions: Although the associations presented in this paper are clearly defined, there exists a high degree of diversity within these. The Karstveld is also extraordinary species rich within the context of the arid to semi-arid Namibian environment.

Taxonomic reference: Klaassen and Kwembeya (2013) for vascular plants, with the exception of the genus Acacia s.l. (Fabaceae), for which Kyalangalilwa et al. (2013) was followed.

Abbreviations: ga = annual grass; gp = perennial grass; GPS = Global Positioning System, referring to a hand-held ground receiver; hl = herb layer, containing all hemicryptophytes, therophytes and geophytes, but excluding grasses (Poaceae); ICPN = International Code of Phytosociological Nomenclature (Theurillat et al. 2021); MAP = mean annual precipitation; NMS = nonmetric multidimensional scaling (Kruskal 1964); RDL = Red Data List (IUCN Species Survival Commission 2001); s1 = tall shrubs, i.e. multi-stemmed phanerophytes between 1 and 5 m; s2 = short shrubs, i.e. chamaephytes or ‘dwarf shrubs’ below 1 m; SOTER = Global and National Soils and Terrain Digital Database (FAO 1993); t1 = tall trees, > 10 m; t2 = short trees, between 5 and 10 m; t3 = low trees, i.e. single-stemmed phanerophytes between 2 and 5 m; TWINSPAN = Two Way Indicator Species Analysis (Roleček et al. 2009); WGS84 = World Geodetic System, 1984 ensemble.

Keywords

Braun-Blanquet, Karst vegetation, Karstveld, modified TWINSPAN, Namibia, Otavi Mountains, syntaxonomy, Terminalietea prunioides, vegetation classification

Introduction

Although much is known about the flora of Namibia, the assemblage of species in relation to their habitat in specific areas (i.e. “vegetation”) is often less well known and understood (Burke and Strohbach 2000; Strohbach 2001). Broad vegetation descriptions as presented by Giess (1998) and Mendelsohn et al. (2002, 2013) provide only limited information on species composition and habitat, and are thus of limited use for land use and conservation planning (Strohbach 2001, 2018). This lack of baseline data also creates problems with monitoring of vegetation condition, as well as the modelling of potential changes in composition in the light of global climate change (Midgley et al. 2005; Scheiter and Higgins 2009; Stewart et al. 2022; L. Naftal et al. unpubl.).

Within the southern African region, mixed attempts have been undertaken to describe vegetation. In east Africa, potential vegetation maps have been published for several countries, at varying levels of detail (Kindt et al. 2011; Lillesø et al. 2011). This includes Zambia and Malawi in the southern African region. Overview vegetation maps have been published for Angola, Botswana and Zimbabwe, yet only few detailed vegetation descriptions have been published (Airy Shaw 1947; Boughey 1961; Teixeira 1968; Ellery et al. 1990; Bekker and De Wit 1991; Timberlake and Nobanda 1993; Timberlake et al. 1993; Bonyongo et al. 2000; Ellery et al. 2003; Murray-Hudson et al. 2011; Revermann et al. 2018; Gonçalves et al. 2021). In contrast, vegetation descriptive work has a long history in South Africa, culminating in the publication of the monograph “The Vegetation of South Africa, Lesotho and Swaziland” (Mucina and Rutherford 2006). Most of the phytosociological work done in South Africa is intended for management of ecosystems, with the described vegetation types forming proxies for these ecosystems (Brown et al. 2013). Accordingly, most such descriptions name the vegetation types informally as “communities”. Brown et al. (2013) recommend that formal descriptions are only to be applied to larger, regional studies. Some examples of such studies are those of Bredenkamp and Theron (1991); Bezuidenhout et al. (1994); Winterbach et al. (2000) and Siebert et al. (2002).

In Namibia, a similar approach to vegetation descriptions has been followed. Early attempts to collect baseline information on natural resources for land use and conservation planning purposes were confined to conservation areas, in particular the Etosha National Park, the Waterberg Plateau Park and the Namib-Naukluft National Park (Robinson 1976; Jankowitz and Venter 1987; Le Roux et al. 1988; see also Kellner 1986; Hines 1992). Since the late 1990s, a project has been started to complete this task (Strohbach 2001, 2014b; Strohbach and Jürgens 2010), with several local and regional vegetation descriptions being published (Strohbach and Petersen 2007; Strohbach and Jankowitz 2012; Jürgens et al. 2013; Strohbach 2013, 2014a, 2019, 2021). With this paper, a first syntaxonomic description at reconnaissance scale of the Karstveld in Namibia is presented.

The Karstveld sensu Giess (1998) has been recognized as an area of high plant diversity, endemism and even with a proportionally high number of Red Data List (RDL) species (Hofmeyr 2004; Loots 2005; Craven and Vorster 2006). Yet exactly this area is also recognised as a hotspot of bush encroachment, threatening extensive cattle farming in these farming communities (Bester 1998; De Klerk 2004; Mendelsohn et al. 2006). A large proportion of the natural vegetation especially on deeper soils has been transformed into arable lands for grain, vegetable and fruit production, making use of the relative high rainfall in the area, as well as abundant ground water resources (Mendelsohn et al. 2000, 2006; Schneider 2004). Environmental pollution through inappropriate mining practices also threaten the natural vegetation (Mileusnić et al. 2014; Mihaljevič et al. 2015).

Study area

The Karstveld sensu Giess (1998) centres around the Otavi Mountain Range between Otavi, Grootfontein and Tsumeb (Figure 1). It extends to the north and east up to the Kalahari sand basin, and the west until it merges into the Mopane savanna. To the south the Karstveld vegetation transitions into the Thornbush savanna (Giess 1998; Strohbach 2002). Swart and Marais (2009) point out that the Karstveld actually extends westward along the limestone and dolomite ridges of the Otavi Group to beyond Opuwo in the Kunene region. For the purpose of this study, we consider only the vegetation of the Karstveld as defined by Giess (1998) and its associated transitional types. The study area covers roughly 25,000 km2.

Figure 1. 

The Karstveld sensu Giess (1998) in Namibia. Mean annual precipitation isohyets are superimposed. Data source: NARIS (2001).

Geology and topography

The Otavi Mountain Range forms the northern platform of the Damara Orogenic Belt. A succession of clastic and carbonate sedimentation resulted in four main strata (South African Committee for Stratigraphy 1980; Miller 1997): The lower Nosib Group consists mainly of quartzite, sandstone and conglomerates. This is followed by the Otavi Group, which is divided into the lower Abenab Subgroup and the upper, more massive Tsumeb Subgroup. Within the Abenab Subgroup a variety of different layers exist, including dolomitic rocks. Of note here is the upper Auros formation, which contains a narrow shale band (the “Auros shales”) (Pickford 1995; Kamona and Günzel 2007; Bechstädt et al. 2018). The upper Tsumeb Subgroup is formed by massive layers of dolomite and limestone (Pickford 1995; Kamona and Günzel 2007). Due to tectonic movement, three deformation events happened during orogeny, resulting in the forming of an extensive synclinorium (Deane 1995; Schneider 2004; Kamona and Günzel 2007). The mountains raise to above 2000 m a.s.l., or roughly between 500 and 800 m above the surrounding plains (Figure 2). The Otavi Group was topped by younger metamorphized sediments (mostly phyllites, but also slates and sandstones) of the Mulden Group; in most cases these have been eroded away, forming the rich soils of the synclinal valleys (e.g. Otavi Valley) (Miller 1997; Schneider 2004; Kamona and Günzel 2007). In various places, aeolian sand and fine-grained alluvial sediments of the Kalahari were deposited in these synclinal valleys (Schneider 2004). The valleys are extensively used for rainfed or irrigated cropping, exploiting the Karst aquifer, often in conjunction with mines (Schneider 2004; Mendelsohn et al. 2006).

Figure 2. 

(a) Topographical map of the study area; (b) simplified geological map of the study area. On these two maps two transects are indicated by red lines. These are presented in Figure 17. Data source: Topography derived from 1 Arc-Second SRTM images (NASA JPL 2013), geological map adapted from the 1:1,000,000 geological map of Namibia (Geological Survey 1980).

The carbonate rocks of the Otavi Mountains are strongly karstified, forming steep and rough mountain slopes (Schneider 2004; Swart and Marais 2009; Grünert 2013). Although a number of springs are known in the Karstveld, no rivers start here as a result of the Karst landscape (Swart and Marais 2009).

To the south the Otavi Mountain Range transitions into the northern zone of the Damara Orogen (Schneider 2004; Kamona and Günzel 2007). Here the topography is dominated by low ridges and mountains of marbles of the Swakop Group. The upper Ugab valley to the west is covered by unconsolidated Quaternary deposits (Schneider 2004; Grünert 2013), resulting in minimal water flow in these headwaters. Other drainage in the vicinity of the Karstveld is the Omuramba Omatako, passing south-east of the study area. An omuramba, plural omirimbi, is the local vernacular for a broad, flat, ephemeral watercourse with no discernible riverbed, very low gradient and highly irregular flow, if any (King 1963; Strohbach 2008b). The Omuramba Omumbonde is a tributary to the Omatako, passing north of the Waterberg and collecting water from the Thornbush savanna / Karstveld transition.

To the east, north and west the Otavi Mountain Range tapers out into the plains of the Ovambo Basin, forming part of the greater Kalahari Basin (Miller 1997). The plains are underlain by Cenozoic sediments of the Kalahari Group, in the form of calcretes with shallow soils (ICC et al. 2000; Schneider 2004). These plains drain into the Omuramba Ovambo which starts east of the Kokasib and Gaikos mountains, turns north and later west to discharge in Fisher’s Pan as part of the Etosha Pan complex (Strohbach 2008b). The Omuramba Ovambo forms the border to the Kalahari Dune system to the east and north and is regarded as the border of the Karstveld sensu Giess (1998).

Climate

The climate of the study area is a typical summer-rainfall, hot, semi-arid steppe (Bsh) following the classification of Köppen (1936). Due to orographic effects, the Otavi Mountain Range receives well over 550 mm mean annual precipitation (Figure 1), whilst the surrounding lowlands receive proportionally less, between 470 mm in the north near Namutoni and 430 mm in the east towards Maroelaboom (Figure 3). The variability of the precipitation is relatively high, with a 26% coefficient of variation (CV) calculated for Tsumeb using the CRU TS4.05 Data set, 1970–2019 (Harris et al. 2014). Mendelsohn et al. (2002) estimate the CV on rainfall to be between 30% and 40% for the area.

Average temperatures can raise to between 34° and 36°C during the hottest months, whilst the average coldest temperatures are between 4° and 8°C during winter. Frost can occur; up to 5 days of frost per year are expected (Mendelsohn et al. 2002). The temperatures north of the Otavi Mountain Range are consistently warmer than within and south of the mountains.

Figure 3. 

Climate diagram for Tsumeb in the central Karstveld. The diagram follows the scheme of Walter et al. (1975), whilst the data was retrieved from climatecharts.net using CRU TS4.05 data, 1970 – 2019 (Harris et al. 2014; Zepner et al. 2021). Further climate charts for nearby localities within the Karstveld are provided in Suppl. material 1.

Methods

Data selected

A data set of 889 relevés with 868 vascular plant species was selected from the phytosociological database of Namibia (GVID ID AF-NA-001) (Strohbach and Kangombe 2012). Details of the selected data subsets are listed in Table 1. These data are also included in the sPlot database (Bruelheide et al. 2019).

All vegetation data were collected according to the standards of the Vegetation Survey of Namibia, i.e. as regular relevés compiled on a 20 m × 50 m plot (1000 m2) plot, whilst plot layout was restricted to a specific habitat (Strohbach 2001, 2014b; Strohbach and Jürgens 2010). In cases where the nature of the habitat did not allow a 20 m × 50 m sized plot (e.g. wetland habitats, rock outcrops), the plot shape was adapted to fit the habitat, without reducing the size, nor moving into a different habitat. The size of 1000 m2 was chosen as suitable for an arid savanna and conforms to size criteria proposed by Brown et al. (2013). Unknown species were collected for identification in the National Herbarium of Namibia (WIND).

For the initial relevés done in 1991/92 (data subset North-Kal), no GPS was available, and the position was determined using 1:50 000 topographic map series of Namibia. Later plot positions could be determined by GPS, initially using the old Schwarzeck reference stan­dard (Merry and Wackerle 2006); as from 2004 the WGS 84 reference system was used. As habitat descriptors the landscape type, local topography, slope and aspect, local lithology (i.e. base material for soils), stone cover and disturbance were noted, using the SOTER scheme (FAO 1993). Only for few relevés soil samples (topsoil and B-horizon) were collected and analysed in the Agri­culture Laboratory of the Ministry of Agriculture, Water and Forestry. Standard analytical procedures were followed (Pansu and Gautheyrou 2006). Additional habitat data was derived from GIS maps based on the position of the survey plots; this included the estimated annual precipitation (NARIS 2001), altitude (NASA JPL 2013), stratigraphy (i.e. the underlying geology) (Geological Survey 1980) and general soil classification (ICC et al. 2000).

Table 1.

Overview of data used for this study. All data form part of GVID ID AF-NA-001 (Strohbach and Kangombe 2012) as well as sPlot (Bruelheide et al. 2019). The quality of the rainy season, which has an influence on the growth of the vegetation, was derived according to the criteria of Botha (1998): Normal years had an annual precipitation of between the 40th and 70th percentile of long-term precipitation records, whilst extreme years had below the 10th (extreme dry) or above the 90th percentile (extreme wet) annual precipitation. The evaluation was done using the CRU TS4.05 Data set for Tsumeb, 1970 – 2019 (Harris et al. 2014).

Relevés Dataset Name Number Year Season quality Surveyor Area of interest Reference (if any)
1301 - 1307 DMP 7 of 422 2004 dry Marianne Strohbach South-east of Grootfontein adjacent to Omurambo Omatako Strohbach (2014)
2259 - 2318 BS-GFT_1999 60 1999 wet B. Strohbach Eastern Karstveld
2772 - 2796 BS_GFT_2003 25 2003 normal B. Strohbach Karstveld-Kalahari transition near Maroelaboom
3183 – 3546 (intermittent) MS_BIOTA 137 of 558 2001-2002 normal Marianne Strohbach Southern edge of Karstveld, transitioning into Thornbush savanna Strohbach (2002)
3813 – 4066 (intermittent) North-Kal 131 of 344 1991-1992 normal very dry B. Strohbach Eastern Karstveld including Omuramba Ovambo and transition to Kalahari
4259 - 4350 Uitkomst_9597 92 1995 & 1997 very dry dry B. Strohbach John Pandeni Research Station near Grootfontein
7683 - 7829 BS_GFT_2007 147 2007 normal B. Strohbach North-east and south of Grootfontein
7830 - 7869 BS_Sargberg_2008 40 2008 normal B. Strohbach Farm Sargberg near Otavi Strohbach (2008)
7902 - 8151 BS_Oshikoto_2008 250 2008 normal B. Strohbach Central and western Karstveld up to Etosha border

Classification procedures

The combined data was imported into Juice (Tichý 2002), and the different layers of species were combined (i.e. structural information was not used in the classification). Likewise, different subspecies and varieties of a species were combined (e.g. Senegalia mellifera and Senegalia mellifera subsp. detinens; Stipagrostis uniplumis and Stipagrostis uniplumis var. uniplumis), unless such subspecies or varieties were known to have distinct different ecological traits and were clearly differentiated in all subsets (e.g. Melinis repens subsp. repens (perennial) vs. Melinis repens subsp. grandiflora (annual)). As Vachellia reficiens (Wawra & Peyr.) Kyal. & Boatwr. and Vachellia luederitzii (Engl.) Kyal. & Boatwr. are very closely related and easily confused during field observations, and both these species occurred in the study area (potentially even together in the same stand) (Schreiber et al. 1970; Mannheimer and Curtis 2009), these have been combined in the classification data set and referred to as “Vachellia reficiens / luede­ritzii”. The final cleaned data set consisted of 889 relevés with 867 species.

A partial data set comprising trees, shrubs, dwarf shrubs and grasses only, was prepared from the original complete relevés. This resulted in a matrix with 306 species only. This data set reduction was done to avoid confusions with incorrect field identifications over various seasons, composition differences due to seasonal variations and general ‘observer bias’ of especially the ephemeral (herbaceous) component of the vegetation. This reduced data set was used for the classification procedure.

An initial classification was done using modified TWINSPAN (Roleček et al. 2009), with average Sørensen as distance measure, but without using pseudospecies. This classification resulted into four clusters, which were interpreted as representing (i) wetlands and associated grasslands, (ii) a transition zone between the Thornbush savanna and the Karstveld (both sensu Giess 1998), (iii) Kalahari type vegetation on deep aeolian sands and (iv) the true Karstveld types. This classification result was used to split the data set into four subsets for further classification, again using the modified TWINSPAN classification algorithm and always using average Sørensen as distance measure. The level of splitting was determined using peaks in crispness values (Botta-Dukát et al. 2005).

The classification of the clusters using partial data was transferred to the full data set. During analysis of the resulting clusters some subdivisions were found to be not ecologically interpretable; thus such branches were merged for an ecological interpretable result. Also, some of the grasslands were found to be classified with the Thornbush savanna. Likewise, a wetland type was classified within the true Karstveld types. These groups were manually moved to Cluster 1 (Wetlands and Grasslands) for easier interpretation. It was also realised that some vegetation types observed during field surveys were not represented in the classification results. To rectify this, a refinement of the classification results was done using Cocktail procedures (Bruelheide and Flintrop 1994; Bruelheide 1997). A detailed account of these Cocktail refinements is presented in the Results section of this paper.

Once an ecologically interpretable result was achieved, phytosociological tables were compiled and the synopsis for various associations extracted. Diagnostic species were determined and sorted using the phi coefficient of association (Chytrý et al. 2002), calculated separately across each subcluster (i.e. for the wet- and grasslands, the Thornbush – Karstveld transistion, the Kalahari and the true Karstveld). For this calculation the numbers of relevés were standardised following Tichý and Chytrý (2006). Species with phi ≥ 0.4 were considered as diagnostic and with phi ≥ 0.6 as highly diagnostic (indicated in bold in the synopsis); however, species with a non-significant fidelity at α = 0.05 using Fisher’s exact test were omitted. Species occurring with at least a 60% frequency were regarded as constant and with at least 80% frequency as highly constant (also indicated in bold in the synopsis).

The resulting terminal units were formally described as associations according to the International Code of Phytosociological Nomenclature (ICPN; Theurillat et al. 2021), unless, due to low numbers of sampled relevés, the validity of such units as unique associations could not be established with certainty. In these cases, the units are treated informally as “communities”. All habitat descriptions follow SOTER and/or the Namibian soil map (FAO 1993; ICC et al. 2000).

Further descriptors of the associations

The average cumulative cover values of the trees, shrubs, dwarf shrubs, perennial grasses, annual grasses and forbs was calculated based on the available growth form data. Structural descriptions follow Edwards (1983). The average species richness in 1,000 m2 per association or community was calculated from the full relevé data. A count of all species within an association or community was taken as the observed Gamma diversity. In addition, an estimate of potential species richness for the association or community was calculated with a first-order Jackknife as proposed by Heltshe and Forrester (1983) and Palmer (1990).

As bush encroachment is a topic in the current study area, Simpson’s Dominance Index and Smith-Wilson’s Index (Evar) (Peet 1974; Smith and Wilson 1996) were calculated for each relevé using Juice (Tichý et al. 2011). Frome these, box-and-whisker plots were constructed per association described.

Environmental gradients

From the original data set, a subset consisting of relevés of the Thornbush – Karst transition, Kalahari and Karstveld (clusters 3, 4 and 5) was compiled for importing into PC-Ord 7.02 (McCune and Mefford 2016). The wetlands and grasslands were not used in this analysis as these are specialized habitats and likely to be outliers in an ordination, confounding the interpretation of relationships within the main savanna types. This data set consisted of 852 relevés and 813 species. Together with this, an environmental data set was compiled, consisting of the following quantitative variables: altitude, slope class, gravel, small, medium, large stone, rock cover (in classes, following SOTER (FAO 1993)), estimated soil depth, mean annual precipitation, observed number of species and sandiness of the soils. This latter variable was derived from the soil type: rock outcrops and leptic Regosols were classed 1; mollic Leptosol associations classed 2; Cambisol associations classed 3; Fluvisols and Arenosols / Calcisols combinations 4, whilst pure Arenosols were classed 5. Missing data for stone cover and slope class was extrapolated by calculating a median value for each variable for the respective association. In addition, the vegetation association, broad vegetation class (i.e. cluster), geology, landscape and soil type were added as categorical variables.

This data set was used to calculate an NMS ordination (Kruskal 1964), using average Sørensen dissimilarity as distance measure. The ordination was calculated in three dimensions, based on an initial scree plot of stress versus dimensions (McCune et al. 2002; Peck 2010). The solutions were calculated with 200 iterations using real and 249 runs using randomised data for a Monte Carlo test. To aid the interpretation of the resulting scatter plots of the ordination results, the environmental variables were overlain as a joint plot onto a scatter diagram of the plots, with an r2 cut-off level of 0.100. Using PC-Ord’s species-contouring feature, the species distribution for some characteristic phanerophytic species was plotted against these main environmental gradients to illustrate their preferred habitat and distribution.

Results and discussion

Initial classification results

The classification results are depicted in Figure 4. In cluster 2 (Thornbush – Karstveld transition) and in cluster 4 (Karstveld proper) grassland types and a wetland type have been identified respectively; these relevé clusters have been moved to Cluster 1 (Wetlands and grasslands) for easier interpretation.

Figure 4. 

Dendrograms of (a) the initial classification of all data, and (b) to (e) of the individual clusters. Only for the Karstveld proper (Terminalietea prunioidis) (e) formal higher order syntaxonomic subdivision have been determined; these are indicated by stippled lines.

Within the grasslands associated with the Thornbush – Karstveld transition, two distinct associations were observed during field work, recognisable by different species composition and different habitats These however were not separated by the modified TWINSPAN classi­fication. For this, Cocktail (Bruelheide and Flintrop 1994; Bruelheide 1997) was employed as follows: Relevés belonging to association 2.1.2.1 were selected based on the occurrence of Themeda triandra, Cymbopogon caesius, Cynodon dactylon and Hyparrhenia hirta. Relevés belonging to association 2.1.2.2 were selected based on the occurrence of Brachiaria serrata, Cymbopogon pospischilii, Jamesbrittenia atropurpurea and Euphorbia spartaria.

Also in the Thornbush – Karstveld transition, thickets with Olea europea subsp. africana were found in the plains and footslopes of the Otavi mountains. These differed from the thornbush shrublands (association 3.1.1.3) further south through a far denser and higher structure and containing several distinct species not found elsewhere. Although these were not separated using modified TWINSPAN, these were recognised as an association based on their composition and physiognomy. To separate this association from the remainder of the thornbush shrublands, Cocktail was employed, searching for relevés containing Olea europea subsp. africana, Enneapogon desvauxii, Elaeodendron transvaalensis, Fingerhuthia africana, Euclea undulata, Vachellia karroo and Croton gratissimus. All selected relevés come from the clusters 3.1.1.3.1 and 3.1.1.3.2 and were grouped as 3.1.1.4.

An abbreviated synoptic table, containing only diagnostic and/or constant species, is provided with each major grouping (Tables 25). Only for the Karstveld proper (Cluster 4) higher syntaxa are described according to the ICPN. The phytosociological tables for these syntaxa are presented in Suppl. material 2, and the corresponding full synoptic tables in Suppl. material 3. All type relevés are highlighted and reproduced in the phytosociological tables.

1. Ephemeral wetlands

The ephemeral wetlands are characterized by the presence of Lagarosiphon muscoides, Nymphoides indica subsp. occidentalis, Eragrostis rotifer, Panicum gilvum, Nymphaea nouchali var. caerulea, Marsilea nubica and Echinochloa species. The vegetation is dominated by the plant families Poaceae (9 species), Cyperaceae (6 species) and Asteraceae (4 species). Within central and northern Namibia, a number of these ephemeral wetlands, locally referred to as vleys, are known (Hines 1993; Clarke 1999). Two such communities were identified within the study area. Due to the low number of relevés and pending a full review of these ephemeral wet- and grasslands, no formal description is presented. An abbreviated synoptic table is presented in Table 2, the full synoptic table is available in Suppl. material 3.

Table 2.

Abbreviated synoptic table for the wetlands and grasslands, showing all species occurring in more than 10% of relevés of these groups, with fidelity (phi coefficient x 100) and frequency of occurrence (%).

Higher grouping 1.1 Wetlands 2.1 Grasslands
2.1.1 Ishana grasslands 2.1.2 Mesic grasslands
Association 1.1.1.1 1.1.1.2 2.1.1.1 2.1.1.2 2.1.2.1 2.1.2.2
No of relevés 4 3 3 11 10 6
Species phi % phi % phi % phi % phi % phi %
Nymphoides indica subsp. occidentalis 100 100 --- 0 --- 0 --- 0 --- 0 --- 0
Eragrostis rotifer 86 100 --- 0 --- 0 --- 18 --- 10 --- 0
Echinochloa pyramidalis 67 50 --- 0 --- 0 --- 0 --- 0 --- 0
Cyperus compressus 67 50 --- 0 --- 0 --- 0 --- 0 --- 0
Nymphaea nouchali var. caerulea 67 50 --- 0 --- 0 --- 0 --- 0 --- 0
Lapeirousia avasmontana --- 0 79 67 --- 0 --- 0 --- 0 --- 0
Marsilea nubica --- 0 79 67 --- 0 --- 0 --- 0 --- 0
Panicum gilvum --- 0 79 67 --- 0 --- 0 --- 0 --- 0
Combretum imberbe --- 50 64 100 --- 0 --- 0 --- 30 --- 17
Sporobolus spicatus --- 0 --- 0 100 100 --- 0 --- 0 --- 0
Leptochloa fusca --- 25 --- 0 87 100 --- 0 --- 0 --- 0
Odyssea paucinervis --- 0 --- 0 86 100 --- 27 --- 0 --- 0
Sporobolus acinifolius --- 0 --- 0 83 100 --- 36 --- 0 --- 0
Chloris virgata --- 0 --- 0 --- 0 89 82 --- 0 --- 0
Willkommia sarmentosa --- 0 --- 0 --- 0 83 73 --- 0 --- 0
Sporobolus ioclados --- 0 --- 0 --- 0 83 73 --- 0 --- 0
Aristida stipoides --- 0 --- 0 --- 0 77 64 --- 0 --- 0
Eragrostis viscosa --- 0 --- 0 --- 0 71 55 --- 0 --- 0
Hirpicium gazanioides --- 0 --- 0 --- 0 71 55 --- 0 --- 0
Dactyloctenium aegyptium --- 0 --- 0 --- 67 66 91 --- 0 --- 0
Sesuvium sesuvioides --- 0 --- 0 --- 0 57 36 --- 0 --- 0
Ipomoea coptica --- 0 --- 0 --- 0 57 36 --- 0 --- 0
Cyperus atriceps --- 0 --- 0 --- 0 57 36 --- 0 --- 0
Commelina subulata --- 0 --- 0 --- 0 57 36 --- 0 --- 0
Blepharis leendertziae --- 0 --- 0 --- 0 57 36 --- 0 --- 0
Sericorema sericea --- 0 --- 0 --- 0 52 45 --- 0 --- 17
Eragrostis trichophora --- 0 --- 0 --- 0 52 45 --- 0 --- 17
Microchloa caffra --- 0 --- 0 --- 0 49 55 --- 20 --- 17
Xerophyta humilis --- 0 --- 0 --- 0 49 27 --- 0 --- 0
Ophioglossum lancifolium --- 0 --- 0 --- 0 49 27 --- 0 --- 0
Themeda triandra --- 0 --- 0 --- 0 --- 0 100 100 --- 0
Elionurus muticus --- 0 --- 0 --- 0 --- 0 81 70 --- 0
Eragrostis lehmanniana --- 0 --- 0 --- 0 --- 0 81 70 --- 0
Hilliardiella oligocephala --- 0 --- 0 --- 0 --- 0 77 90 --- 33
Ipomoea oblongata --- 0 --- 0 --- 0 --- 0 75 60 --- 0
Hypoxis iridifolia --- 0 --- 0 --- 0 --- 0 71 70 --- 17
Eragrostis superba --- 0 --- 0 --- 0 --- 0 71 70 --- 17
Hermannia depressa --- 0 --- 0 --- 0 --- 0 67 50 --- 0
Corchorus asplenifolius --- 0 --- 0 --- 0 --- 0 67 50 --- 0
Hermannia eenii --- 0 --- 0 --- 0 --- 0 67 50 --- 0
Wahlenbergia undulata --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Solanum delagoense --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Lantana angolensis --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Hyparrhenia hirta --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Convolvulus sagittatus --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Hibiscus trionum --- 0 --- 0 --- 0 --- 0 60 40 --- 0
Pollichia campestris --- 0 --- 0 --- 0 --- 0 55 50 --- 17
Andropogon gayanus var. polycladus --- 0 --- 0 --- 0 --- 0 55 50 --- 17
Cymbopogon caesius --- 0 --- 0 --- 0 --- 0 55 60 --- 33
Solanum lichtensteinii --- 0 --- 0 --- 0 --- 0 55 60 --- 33
Osteospermum muricatum --- 0 --- 0 --- 0 --- 0 51 30 --- 0
Alternanthera pungens --- 0 --- 0 --- 0 --- 0 51 30 --- 0
Urochloa oligotricha --- 0 --- 0 --- 0 --- 0 51 30 --- 0
Listia heterophylla --- 0 --- 0 --- 0 --- 0 51 30 --- 0
Indigofera vicioides --- 0 --- 0 --- 0 --- 0 51 30 --- 0
Cynodon dactylon --- 0 --- 0 --- 33 --- 18 50 70 --- 17
Setaria pumila --- 0 --- 0 --- 0 --- 0 47 40 --- 17
Euphorbia inaequilatera --- 0 --- 0 --- 0 --- 0 47 40 --- 17
Urochloa brachyura --- 0 --- 0 --- 0 --- 18 46 50 --- 17
Fingerhuthia africana --- 0 --- 0 --- 0 --- 0 --- 10 94 100
Cymbopogon pospischilii --- 0 --- 0 --- 0 --- 0 --- 40 81 100
Geigeria otaviensis --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Helichrysum cerastioides var. aurosicum --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Jamesbrittenia atropurpurea subsp. pubescens --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Melhania virescens --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Striga bilabiata --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Dicoma anomala --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Eriocephalus luederitzianus --- 0 --- 0 --- 0 --- 0 --- 0 79 67
Brachiaria serrata --- 0 --- 0 --- 0 --- 0 --- 20 78 83
Scabiosa columbaria --- 0 --- 0 --- 0 --- 0 --- 10 72 67
Anginon streyi --- 0 --- 0 --- 0 --- 0 --- 0 67 50
Eragrostis nindensis --- 0 --- 0 --- 0 --- 18 --- 0 67 67
Tarchonanthus camphoratus --- 0 --- 0 --- 0 --- 0 --- 40 57 67
Rhynchosia totta --- 0 --- 0 --- 0 --- 0 --- 0 54 33
Hibiscus caesius --- 0 --- 0 --- 0 --- 0 --- 0 54 33
Kohautia aspera --- 0 --- 0 --- 0 --- 0 --- 0 54 33
Euphorbia spartaria --- 0 --- 0 --- 0 --- 0 --- 0 54 33
Lagarosiphon muscoides 54 75 45 67 --- 0 --- 0 --- 0 --- 0
Heteropogon contortus --- 0 --- 0 --- 0 --- 0 49 80 68 100
Tragus racemosus --- 0 --- 0 --- 33 39 45 --- 10 --- 0
Dichrostachys cinerea --- 0 --- 0 --- 0 --- 18 --- 30 --- 17
Schkuhria pinnata --- 0 --- 0 --- 0 --- 0 38 40 --- 33
Oxalis depressa --- 0 --- 0 --- 0 --- 0 38 40 --- 33
Aristida effusa --- 0 --- 0 --- 33 --- 0 --- 20 --- 33
Tragus berteronianus --- 0 --- 0 --- 0 --- 9 --- 30 --- 17
Kyllinga alba --- 0 --- 0 --- 0 --- 18 --- 30 --- 0
Nidorella resedifolia --- 0 --- 0 --- 0 --- 0 --- 30 --- 33
Eragrostis echinochloidea --- 0 --- 0 --- 33 --- 0 --- 10 --- 33
Bulbostylis hispidula --- 0 --- 0 --- 0 --- 27 --- 0 --- 17
Melinis repens subsp. grandiflora --- 0 --- 0 --- 0 --- 9 --- 20 --- 17
Aristida adscensionis --- 0 --- 0 --- 0 --- 18 --- 20 --- 0
Brachiaria nigropedata --- 0 --- 0 --- 0 --- 0 --- 30 --- 17
Anthephora pubescens --- 0 --- 0 --- 0 --- 0 --- 30 --- 17
Euclea undulata --- 0 --- 0 --- 0 --- 0 --- 30 --- 17
Vachellia reficiens / luederitzii --- 25 --- 0 --- 0 --- 0 --- 10 --- 17
Aristida rhiniochloa --- 0 --- 0 --- 33 --- 0 --- 10 --- 17
Gisekia africana --- 0 --- 0 --- 0 --- 18 --- 0 --- 17
Aristida meridionalis --- 0 --- 0 --- 0 --- 18 --- 0 --- 17
Indigofera charlieriana --- 0 --- 0 --- 0 --- 9 --- 10 --- 17
Tephrosia dregeana var. dregeana --- 0 --- 0 --- 0 --- 9 --- 20 --- 0
Pogonarthria fleckii --- 0 --- 0 --- 0 --- 18 --- 0 --- 17
Ziziphus mucronata --- 0 --- 0 --- 0 --- 0 --- 20 --- 17
Monsonia glauca --- 0 --- 0 --- 0 --- 0 --- 20 --- 17
Commelina livingstonii --- 0 --- 0 --- 0 --- 0 --- 20 --- 17
Aristida congesta subsp. congesta --- 0 --- 0 --- 0 --- 0 --- 20 --- 17
Thesium xerophyticum --- 0 --- 0 --- 0 --- 0 --- 10 --- 33
Panicum coloratum --- 25 --- 0 --- 0 --- 0 --- 10 --- 0
Vahlia capensis --- 0 --- 33 --- 0 --- 9 --- 0 --- 0

Overview of the ephemeral wetlands:

1.1 Undefined upper hierarchy

1.1.1.1 Nymphoides indica-Echinochloa pyramidalis community

1.1.1.2 Panicum gilvum-Marsilea nubica community

1.1.1.1 Nymphoides indica - Echinochloa pyramidalis community

Number of relevés: 4

Number of species observed: 22

Estimated number of species: 34

Average species density in 1000 m2: 9

Diagnostic species: Nymphoides indica subsp. occidentalis, Eragrostis rotifer, Nymphaea nouchali var. caerulea, Echinochloa pyramidalis, Cyperus compressus, Lagarosiphon muscoides

These vleys occur embedded in the Omuramba Ovambo, surrounded by a fringe of Terminalio prunioidis–Spirostachyetum africanae (see 5.2.3.1). The vley vegetation is dominated by the aquatic plants Lagarosiphon muscoides, Eragrostis rotifer, Echinochloa pyramidalis, Schoenoplectus corymbosus, Nymphoides indica subsp. occidentalis, Leptochloa fusca and Echinochloa crus-galli. The presence of the geophytic hydrophyte Nymphaea nouchali indicates that these vleys are generally deeper (about 1 m or more), and regularly filled with water, allowing this species to survive. Similar vleys have been found to the east in the Maroelaboom Dune Belt and the Tsumkwe district (Hines 1993) (Figures 5a, 6a).

Figure 5. 

Typical structure of the associations of the wet- and grasslands: (a) Nymphoides indica–Echinochloa pyramidalis community; (b) Panicum gilvum–Marsilea nubica community; (c) Sporobolus spicatus–Odyssea paucinervis community; (d) Aristido stipoidis-Willkommietum sarmentosae; (e) Hilliardiello oligocephalae-Themedetum triandrae; (f) Geigerio otaviensis-Fingerhuthietum africanae.

Figure 6. 

Typical views of the associations of the wet- and grasslands: (a) Example of the Nymphoides indica-Echinochloa pyramidalis community, relevé 4097, ca 50 km east of the study area; (b) Panicum gilvum-Marsilea nubica community, relevé 7776; (c) Aristido stipoidis-Willkommietum sarmentosae, relevé 7773, foreground. In the background is a Terminalio prunioidis-Spirostachyetum africanae island; (d) Hilliardiello oligocephalae-Themedetum triandrae, relevé 7947; (e) Geigerio otaviensis-Fingerhuthietum africanae, relevé 7960; (f) soil surface of the Geigerio otaviensis-Fingerhuthietum africanae habitat at relevé 7960.

1.1.1.2 Panicum gilvum-Marsilea nubica community

Number of relevés: 3

Number of species observed: 14

Estimated number of species: 20

Average species density in 1000 m2: 7

Diagnostic species: Panicum gilvum, Marsilea nubica, Lapeirousia avasmontana, Combretum imberbe, Lagarosiphon muscoides

The Panicum gilvum-Marsilea nubica community is found in feeder streams to the Omuramba Ovambo system, and is dominated by the aquatic species Marsilea nubica, Marsdenia macrantha and Lagarosiphon muscoides. A similar association has been described by Strohbach (2014a) in the eastern communal areas, south-east of the present study area. The absence of the hydrophytes Nymphaea, Nymphoides and Echinochloa indicates a shallow (considerably less than 1 m) and very temporary water habitat, which is not regularly flooded (Figures 5b, 6b). The few relevés were sampled at an altitude around 1190 m a.s.l.

2. Grasslands

Grasslands are limited in extent in Namibia and are often associated with wetland systems or desert environments. Within the study area, these are dominated by the plant families Poaceae (65 species), Fabaceae (22 species) and Asteraceae (21 species). Two higher order groupings could be recognised, but at this stage are not formally described, pending an extensive revision of these grasslands in comparison to other similar types in Namibia, as well as in the South African Grassland Biome (Mucina and Rutherford 2006).

Overview of the grassland groupings:

2.1 Undefined upper hierarchy

2.1.1 Ishana grasslands (Sporobolus-dominated)

2.1.1.1 Sporobolus spicatus-Odyssea paucinervis community

2.1.1.2 Aristido stipoidis-Willkommietum sarmentosae

2.1.2 Mesic grasslands

2.1.2.1 Hilliardiello oligocephalae-Themedetum triandrae

2.1.2.2 Geigerio otaviensis-Fingerhuthietum africanae

2.1.1 Ishana grasslands (Sporobolus-dominated)

The Sporobolus-dominated grasslands are associated with pans and shallow water courses, typically the ishana and pans of the Cuvelai Delta (Le Roux et al. 1988; Clarke 1999; Mendelsohn et al. 2013) (ishana, plural, singular: oshana, vernacular for seasonally flooded shallow water courses in northern Namibia). The two associations described here resemble the Andoni grasslands as described by Le Roux et al. (1988), but distinct differences in species composition as well as height and density of the sward differentiate them from these.

2.1.1.1 Sporobolus spicatus-Odyssea paucinervis community

Number of relevés: 3

Number of species observed: 10

Estimated number of species: 13

Average species density in 1000 m2: 6

Diagnostic species: Sporobolus spicatus, Leptochloa fusca, Odyssea paucinervis, Sporobolus acinifolius

Constant species: Dactyloctenium aegyptium

Along the eastern fringe of the Omuramba Ovambo, on the farm Nukuwis, occurs an isolated clay pan. The pan is zoned in three concentric zones: The outer ring is a mixture of Sporobolus spicatus, with some Odyssea paucinervis and Cynodon dactylon, the following ring is dominated by Leptochloa fusca, whilst the inner ring is dominated by Sporobolus acinifolius. In the centre is a bare patch. The structure is best described as a low, open grassland (Figure 5c).

The soils consist of a heavy, whitish clay with 73% clay in the topsoil, increasing to 83% in the B-horizon. The pH ranged between 9.8 to 10.0, with the soil conductivity ranging between 4,700 to 6,480 µS/cm. Sodium content of the soils was 12,200 ppm. The high salinity is reflected in the presence of Odyssea paucinervis (Gibbs Russell et al. 1990; Müller 2007), but overall very low species richness. All stands grew at 1198 m a.s.l.

2.1.1.2 Aristido stipoidis-Willkommietum sarmentosae ass. nov.

Number of relevés: 11

Number of species observed: 67

Estimated number of species: 99

Average species density in 1000 m2: 16

Type relevé: 2781 (holotypus), sampled on 2 April 2003 at 19.17861°S, 18.61083°E (Begus)

Hyphaene petersiana (t2) 0.1%, Hyphaene petersiana (s1) 1%, Eragrostis trichophora (gp) 10%, Willkommia sarmentosa (gp) 10%, Sporobolus ioclados (gp) 5%, Odyssea paucinervis (gp) 2%, Microchloa caffra (gp) 1%, Aristida stipoides (ga) 2%, Eragrostis viscosa (ga) 2%, Chloris virgata (ga) 1%, Dactyloctenium aegyptium (ga) 1%, Pogonarthria fleckii (ga) 1%, Commelina erecta (hl) 1%, Hirpicium gazanioides (hl) 1%, Kyllinga alba (hl) 1%, Portulaca kermesina (hl) 1%, Sesuvium sesuvioides (hl) 1%

Diagnostic species: Chloris virgata, Willkommia sarmentosa, Sporobolus ioclados, Aristida stipoides, Hirpi­cium gazanioides, Eragrostis viscosa, Dactyloctenium aegyptium, Sesuvium sesuvioides, Ipomoea coptica, Cyperus atriceps, Commelina subulata, Blepharis leendertziae, Sericorema sericea, Eragrostis trichophora, Microchloa caffra, Xerophyta humilis, Ophioglossum lancifolium

The Aristido stipoidis-Willkommietum sarmentosae form the matrix of the Omuramba Ovambo vegetation, being the typical short open grasslands of the ‘Parkiesveld’ (Figures 5d, 6c). They are dominated by Aristida stipoides, Sporobolus ioclados, Xerophyta humilis, Willkommia sarmentosa, Sporobolus acinifolius, Sericorema sericea and Eragrostis trichophora. Embedded in this grassland are islands of Terminalio prunioidis-Spirostachyetum africanae, often associated with a central pan of the Nymphoides indica-Echinochloa community (Figure 7a). A similar landscape has also been described for the water course systems in the KAZA Transfrontier Conservation area, albeit with different species (Schaffer-Smith et al. 2022).

The A-horizon is about 10 cm deep and consists of a near-pure, white sand (94% sand and 5% clay), with a pH of 7.3 and an electric conductivity of 49 µS/cm. The B-hori­zon is slightly loamier with 7% clay and 92% sand and has a pH of 9.7. The steeply increased electric conductivity (1117 µS/cm) is due to sodium and calcium collecting in this horizon (1380 ppm Na and 1322 ppm Ca). The horizon has also a gleyic, mottled appearance. The Aristido stipoidis-Willkommietum sarmentosae occur at an altitudinal range of between 1164 and 1201 m a.s.l.

Figure 7. 

a Aerial image showing the mosaic of vegetation associations. (a) A portion of the Omuramba Ovambo at the farm Nukuwis. Alternatively to the Terminalietum sericeo-prunioidis, the Combreto apiculati-Terminalietum prunioidis can surround this mosaic, depending on the depth of the Kalahari sand cover. (b) The central Otavi mountains north of Kombat. The mountains are covered by one of the three associations of the Commiphoro glaucescentis- Kirkietalia acuminatae, depending on steepness and massiveness of the rocks, whilst the light-coloured bands on top of the mountains represent the Auros shales with a cover of Geigerio otaviensis-Fingerhuthietum africanae. Image source: Microsoft Maps (Bing Maps).

2.1.2 Mesic grasslands

The Mesic grasslands found within the Karstveld resemble the Grassland Biome in South Africa, in particular the Highveld Mesic Grasslands (Mucina and Rutherford 2006). As these grasslands contain several species which are not associated with the Grassland Biome, even restricted range endemics, two associations are recognized here.

2.1.2.1 Hilliardiello oligocephalae - Themedetum triandrae ass. nov.

Number of relevés: 10

Number of species observed: 115

Estimated number of species: 177

Average species density in 1000 m2: 30

Type relevé: 7953 (holotypus), sampled on 18 February 2008 at 19.63861°S, 17.77306°E (Neu Sommerau)

Heteropogon contortus (gp) 20%, Brachiaria nigropedata (gp) 10%, Elionurus muticus (gp) 10%, Themeda triandra (gp) 10%, Anthephora pubescens (gp) 5%, Cymbopogon pospischilii (gp) 2%, Andropogon gayanus (gp) 1%, Brachiaria serrata (gp) 1%, Cymbopogon caesius (gp) 1%, Eragrostis lehmanniana var. lehmanniana (gp) 1%, Microchloa caffra (gp) 0.5%, Hilliardiella oligocephala (hl) 2%, Thesium xerophyticum (hl) 2%, Clematis villosa subsp. villosa (hl) 1%, Hypoxis iridifolia (hl) 1%, Ipomoea oblongata (hl) 1%, Scabiosa columbaria (hl) 1%, Chamaecrista mimosoides (hl) 0.5%, Corchorus asplenifolius (hl) 0.5%, Hermannia eenii (hl) 0.5%, Tephrosia dregeana var. dregeana (hl) 0.5%

Diagnostic species: Themeda triandra, Eragrostis lehmanniana, Elionurus muticus, Hilliardiella oligocephala, Ipomoea oblongata, Hypoxis iridifolia, Eragrostis superba, Hermannia eenii, Hermannia depressa, Corchorus asple­nifolius, Wahlenbergia undulata, Solanum delagoense, Lantana angolensis, Hyparrhenia hirta, Hibiscus trionum, Convolvulus sagittatus, Pollichia campestris, Andropogon gayanus var. polycladus, Solanum lichtensteinii, Cymbopogon caesius, Urochloa oligotricha, Osteospermum muricatum, Listia heterophylla, Indigofera vicioides, Alternanthera pungens, Cynodon dactylon, Heteropogon contortus, Setaria pumila, Euphorbia inaequilatera, Urochloa brachyura

The Hilliardiello oligocephalae-Themedetum triandrae forms a tall, closed grassland very similar to the Highveld Grasslands of the central and eastern Grassland Biome in South Africa (Mucina and Rutherford 2006) (Figures 5e, 6d). It is dominated by the grass species Heteropogon contortus, Elionurus muticus, Cymbopogon caesius, Themeda triandra, Setaria pumila, Hyparrhenia hirta, Urochloa oligotricha and Cynodon dactylon, whilst Vachellia karroo is the main encroaching species. As such, these grasslands are to be regarded as fire-climax grasslands. The regular occurrence of savanna and dryland species like Andropogon gayanus, Hermannia eenii, Lantana angolensis and Thesium xerophyticum (based on distribution data from GBIF 2022) differentiates this association from the South African Grassland Biome associations.

The Hilliardiello oligocephalae-Themedetum triandrae occur in intermontane valleys filled with deep red soils derived from phyllites of the Mulden Group. They occur at altitudes between 1460 and 1860 m a.s.l., on gently undulating, undulating and rolling slopes. No obvious stone cover has been observed. Next to bush encroachment and erosion, these grasslands are threatened by tillage for crop production. Most of the original vegetation in the Otavi valley has been transformed in this way; only in the Sommerau – Gauss valley north of Kombat pristine examples were found.

2.1.2.2 Geigerio otaviensis - Fingerhuthietum africanae ass. nov.

Number of relevés: 6

Number of species observed: 89

Estimated number of species: 140

Average species density in 1000 m2: 27

Type relevé: 7960 (holotypus), sampled on 19 February 2008 at 19.57389°S, 17.70111°E (Gauss)

Helichrysum cerastioides var. aurosicum (s2) 1%, Amphiglossa triflora (s2) 0.5%, Eriocephalus luederitzianus (s2) 0.5%, Jamesbrittenia atropurpurea subsp. pubescens (s2) 0.5%, Tarchonanthus camphoratus (s2) 0.5%, Fingerhuthia africana (gp) 20%, Cymbopogon pospischilii (gp) 10%, Heteropogon contortus (gp) 10%, Brachiaria serrata (gp) 5%, Eragrostis nindensis (gp) 1%, Geigeria otaviensis (hl) 1%, Striga bilabiata (hl) 1%, Dicoma anomala (hl) 0.5%, Scabiosa columbaria (hl) 0.5%, Anginon streyi (hl) 0.1

Diagnostic species: Fingerhuthia africana, Cymbopogon pospischilii, Striga bilabiata, Melhania virescens, Jamesbrittenia atropurpurea subsp. pubescens, Helichrysum cerastioides var. aurosicum, Geigeria otaviensis, Eriocephalus luederitzianus, Dicoma anomala, Brachia­ria serrata, Scabiosa columbaria, Heteropogon contortus, Eragrostis nindensis, Anginon streyi, Tarchonanthus camphoratus, Rhynchosia totta, Kohautia aspera, Hibiscus caesius, Euphorbia spartaria

The Geigerio otaviensis–Fingerhuthietum africanae forms a short, moderately closed grassland dominated by Heteropogon contortus, Cymbopogon pospischilii and Fingerhuthia africana (Figures 5g, 6f). Conspicuous are also the dwarfshrubs Jamesbrittenia atropurpurea subsp. pubescens, Helichrysum cerastioides var. aurosicum, Eriocephalus luederitzianus and the restricted-range endemic Geigeria otaviensis. The occurrence of the savanna and dryland species Fingerhuthia africana, Melhania virescens, Jamesbrittenia atropurpurea subsp. pubescens, Eriocephalus luederitzianus, Euphorbia spartaria (based on distribution data from GBIF 2022) as well as the restricted-range endemic Geigeria otaviensis (Loots 2005) differentiate this association from similar associations in the Grassland Biome of South Africa. These grasslands occur on Auros shale bands as part of the Auros formation in the Abenab subgroup (Pickford 1995; Bechstädt et al. 2018), at an altitude of between 1950 and 1990 m a.s.l., on undulating to rolling slopes at the peak of the Otavi mountain range. The soils are extremely shallow, basically consisting of skeletal stone fragments of the Auros shale bands (Figure 6f). Although the extend of these grasslands is very limited, they are rather conspicuous on the mountain tops along the Otavi Valley (Figure 7b).

3. Thornbush savanna – Karst transition

The southern Karstveld vegetation transitions into the Thornbush savanna sensu Giess (1998) to the south, without a distinct ‘border’. Many of the units found are strongly influenced by shallow subsurfacing rock formations of the Otavi group, thus the very strong relations to the Karstveld Proper types. Within this study area, the thornbush savanna is dominated by the families Poaceae (105 species), Faba­ceae (74 species) and Asteraceae (48 species). Four associations were identified within the study area belonging to this class; these are however not assigned to any orders or alliances pending further revision of the Thornbush savanna types. An abbreviated synoptic table is presented in Table 3, whilst the full synoptic table is available in Suppl. material 3.

Table 3.

Abbreviated synoptic table for the Thornbush savanna - Karstveld transition, showing all species occurring in more than 10% of relevés of this group, with fidelity (phi coefficient × 100) and frequency of occurrence (%).

Association 3.1.1.1 3.1.1.2 3.1.1.3 3.1.1.4
Subassociation 3.1.1.3.1 3.1.1.3.2
No of relevés 93 56 71 145 32
Species phi % phi % phi % phi % phi %
Brachiaria nigropedata 59 54 --- 5 --- 0 --- 1 --- 6
Anthephora pubescens 53 87 --- 7 --- 1 --- 23 27 63
Sesamum triphyllum 51 45 --- 2 --- 0 --- 3 --- 9
Rotheca myricoides 51 39 --- 0 --- 0 --- 1 --- 6
Schmidtia pappophoroides 49 78 --- 34 --- 7 --- 23 --- 19
Vernonia fastigiata 48 37 --- 4 --- 3 --- 2 --- 0
Dicoma anomala 46 38 --- 2 --- 0 --- 1 --- 9
Ozoroa paniculosa 43 68 --- 34 --- 3 --- 17 --- 22
Tragus racemosus 43 68 --- 4 --- 7 --- 19 20 47
Triraphis purpurea 42 37 --- 2 --- 4 --- 7 --- 3
Indigofera charlieriana 42 66 --- 4 --- 7 --- 20 18 44
Indigofera pechuelii 40 20 --- 0 --- 0 --- 1 --- 0
Hermannia eenii --- 5 58 54 --- 6 --- 3 --- 0
Aristida pilgeri --- 5 55 43 --- 0 --- 1 --- 0
Melhania acuminata --- 2 55 54 --- 4 --- 11 --- 3
Vachellia erioloba --- 6 49 57 --- 14 --- 12 --- 3
Terminalia sericea --- 0 49 30 --- 0 --- 1 --- 0
Senegalia cinerea --- 4 47 59 --- 20 --- 12 --- 9
Dicoma schinzii --- 15 45 45 --- 1 --- 5 --- 3
Waltheria indica --- 9 43 50 --- 4 --- 17 --- 6
Digitaria seriata --- 0 41 29 --- 1 --- 3 --- 3
Heliotropium nelsonii --- 3 --- 0 52 48 --- 11 --- 3
Leucosphaera bainesii --- 2 --- 0 52 45 --- 12 --- 0
Monechma genistifolium --- 0 --- 0 51 37 --- 5 --- 0
Ipomoea obscura var. obscura --- 1 --- 2 49 35 --- 3 --- 0
Asparagus cooperi --- 0 --- 0 46 30 --- 4 --- 0
Eragrostis porosa --- 4 --- 2 43 48 --- 14 --- 13
Solanum tettense var. renschii --- 0 --- 2 43 34 --- 7 --- 3
Hibiscus calyphyllus --- 0 --- 2 42 35 --- 10 --- 3
Geigeria acaulis --- 0 --- 2 41 23 --- 0 --- 0
Boscia albitrunca --- 0 --- 9 41 48 --- 16 --- 13
Hibiscus palmatus --- 0 --- 0 41 23 --- 2 --- 0
Ptycholobium biflorum subsp. angolensis --- 3 --- 0 40 42 --- 19 --- 6
Corchorus tridens --- 3 --- 0 63 58 --- 9 --- 0
Olea europaea subsp. africana --- 0 --- 0 --- 0 --- 0 100 100
Fingerhuthia africana 30 74 --- 4 --- 7 --- 47 46 91
Digitaria eriantha --- 1 --- 0 --- 0 --- 5 45 31
Euclea undulata 21 62 --- 21 --- 3 --- 39 43 84
Croton gratissimus --- 3 --- 7 --- 14 22 46 41 63
Kohautia aspera --- 10 --- 4 --- 0 --- 8 40 38
Heteropogon contortus 28 81 --- 27 --- 8 --- 59 38 91
Senegalia mellifera subsp. detinens --- 88 --- 89 --- 87 9 97 --- 97
Dichrostachys cinerea --- 77 13 88 --- 77 --- 76 --- 66
Grewia flava --- 73 --- 61 --- 73 --- 76 --- 66
Combretum hereroense 24 85 --- 55 --- 10 18 79 20 81
Vachellia reficiens / luederitzii --- 29 --- 68 21 87 --- 69 21 88
Eragrostis trichophora --- 68 --- 45 21 80 --- 52 --- 56
Tarchonanthus camphoratus 30 85 --- 21 --- 39 --- 63 --- 66
Stipagrostis uniplumis var. uniplumis 17 75 22 80 --- 42 --- 50 --- 47
Melhania virescens --- 65 --- 7 --- 48 15 70 32 88
Lantana angolensis --- 59 --- 41 --- 51 --- 59 --- 69
Urochloa brachyura 16 67 --- 50 --- 45 --- 50 --- 41
Seddera suffruticosa 21 71 --- 16 --- 41 --- 57 --- 66
Ziziphus mucronata --- 51 --- 59 --- 39 --- 50 18 72
Melinis repens subsp. grandiflora 23 70 --- 21 --- 52 --- 47 --- 44
Enneapogon scoparius 17 61 --- 5 --- 24 16 60 28 72
Otoptera burchellii 16 60 --- 23 14 58 --- 43 --- 38
Eragrostis echinochloidea --- 25 --- 9 --- 51 20 66 33 78
Cenchrus ciliaris --- 23 --- 4 29 75 12 57 24 69
Searsia marlothii 10 56 --- 21 --- 10 11 57 39 84
Combretum imberbe 31 69 --- 39 --- 6 --- 41 --- 38
Aristida rhiniochloa 32 68 --- 21 --- 27 --- 37 --- 31
Peltophorum africanum 18 56 14 52 --- 3 --- 34 --- 47
Enneapogon cenchroides --- 42 --- 7 22 56 --- 36 --- 38
Aristida effusa --- 41 --- 9 --- 45 12 44 --- 25
Grewia flavescens --- 9 --- 45 11 49 4 42 --- 47
Ocimum americanum var. americanum --- 40 --- 41 --- 32 --- 35 --- 25
Hibiscus caesius --- 32 --- 11 --- 7 14 45 36 66
Aptosimum decumbens --- 37 --- 29 --- 28 --- 30 --- 28
Ehretia rigida --- 10 --- 11 33 59 9 37 --- 28
Pogonarthria fleckii 24 52 --- 27 --- 37 --- 17 --- 16
Sericorema sericea 24 51 --- 4 --- 10 --- 30 23 50
Phyllanthus maderaspatensis --- 29 --- 18 --- 31 --- 31 --- 31
Terminalia prunioides --- 12 --- 21 --- 14 28 49 --- 28
Aristida adscensionis 21 45 --- 9 --- 37 --- 22 --- 19
Aristida congesta subsp. congesta 24 48 12 38 --- 32 --- 11 --- 6
Urochloa oligotricha 9 37 --- 4 --- 27 --- 23 27 53
Evolvulus alsinoides --- 12 21 48 18 45 --- 21 --- 19
Tragus berteronianus --- 31 --- 4 20 42 --- 22 --- 25
Eragrostis nindensis 15 33 --- 2 --- 10 15 34 --- 28
Grewia bicolor --- 11 --- 21 28 45 --- 26 --- 6
Limeum sulcatum 24 45 --- 5 --- 8 --- 17 26 47
Tephrosia dregeana var. dregeana --- 27 --- 29 --- 8 --- 22 --- 31
Ocimum filamentosum --- 6 --- 5 21 38 14 32 --- 22
Pavonia burchellii --- 12 --- 23 12 34 --- 21 --- 28
Geigeria ornativa --- 8 --- 29 --- 28 --- 26 --- 16
Commiphora glandulosa --- 22 --- 18 --- 0 18 33 --- 22
Nidorella resedifolia --- 8 --- 13 22 38 9 27 --- 16
Gymnosporia senegalensis --- 6 --- 16 --- 7 12 33 36 53
Stipagrostis hirtigluma subsp. hirtigluma --- 1 --- 2 --- 20 33 41 --- 19
Clerodendrum ternatum --- 4 --- 18 13 30 12 28 --- 16
Rhynchosia totta --- 16 --- 14 --- 15 9 26 --- 25
Searsia ciliata 32 44 --- 13 --- 10 --- 13 --- 16
Enneapogon desvauxii --- 13 --- 0 --- 11 8 28 40 53
Kyphocarpa angustifolia 16 33 15 32 --- 24 --- 6 --- 6
Commelina livingstonii 39 49 --- 4 --- 10 --- 10 --- 22
Catophractes alexandri --- 9 --- 5 --- 17 20 31 --- 19
Leucas pechuelii --- 4 --- 2 38 44 11 24 --- 6
Phyllanthus pentandrus --- 8 --- 11 --- 21 5 23 19 34
Heliotropium ovalifolium --- 9 --- 14 --- 6 3 23 37 50
Panicum coloratum 36 45 --- 5 --- 6 --- 8 --- 25
Eragrostis rigidior --- 5 26 39 14 30 --- 13 --- 6
Melinis repens subsp. repens --- 23 20 34 --- 11 --- 11 --- 13
Eriocephalus luederitzianus 14 26 --- 0 --- 14 --- 19 --- 19
Commiphora angolensis --- 6 --- 5 --- 23 13 24 --- 16
Chascanum pinnatifidum --- 12 --- 4 31 35 --- 19 --- 0
Acalypha segetalis 31 39 --- 0 --- 3 --- 12 --- 25
Commiphora africana --- 15 --- 0 --- 10 11 23 18 28
Pupalia lappacea --- 9 --- 5 23 34 --- 14 --- 22
Combretum apiculatum 12 26 --- 11 --- 0 --- 15 20 31
Rhynchosia minima 10 24 --- 2 --- 11 --- 15 17 28
Pogonarthria squarrosa 20 30 35 41 --- 1 --- 6 --- 0
Eragrostis superba 37 41 --- 2 --- 3 --- 10 --- 19
Hermannia tomentosa 26 33 --- 13 --- 8 --- 10 --- 9
Cymbopogon pospischilii 39 44 --- 4 --- 1 --- 6 --- 25
Helinus spartioides 19 26 --- 5 --- 11 --- 14 --- 9
Raphionacme lanceolata --- 12 --- 2 --- 21 --- 18 --- 13
Acrotome inflata --- 17 --- 5 22 31 --- 7 --- 16
Solanum lichtensteinii 12 23 --- 2 18 27 --- 7 --- 13
Aristida stipoides 35 37 --- 0 --- 3 --- 8 --- 19
Sida ovata --- 4 25 32 --- 13 --- 13 --- 9
Andropogon gayanus var. polycladus 32 35 --- 7 --- 0 --- 6 --- 19
Eragrostis lehmanniana --- 2 31 34 --- 0 10 19 --- 9
Gisekia africana 26 31 --- 7 --- 3 --- 7 --- 19
Andropogon chinensis 30 32 --- 2 --- 3 --- 7 --- 19
Brachiaria deflexa --- 6 --- 0 19 25 --- 12 --- 19
Albizia anthelmintica --- 2 --- 5 31 30 --- 15 --- 0
Bothriochloa radicans --- 5 --- 2 --- 11 24 22 --- 3
Mundulea sericea --- 5 --- 2 --- 1 12 20 30 31
Commiphora pyracanthoides --- 0 --- 2 37 34 --- 13 --- 6
Pentarrhinum insipidum 8 19 --- 5 --- 3 --- 8 30 34
Hyphaene petersiana --- 13 27 27 --- 1 --- 11 --- 0
Oxygonum alatum --- 12 --- 7 14 21 --- 7 --- 13
Commelina benghalensis --- 2 --- 5 34 34 --- 8 --- 9
Ruellia species --- 1 --- 0 30 27 11 16 --- 3
Aizoon virgatum --- 0 --- 0 32 30 --- 14 --- 6
Monechma spartioides --- 0 27 30 --- 6 --- 12 --- 16
Hermannia modesta --- 11 --- 2 24 27 --- 6 --- 13
Sporobolus panicoides --- 4 --- 4 --- 4 8 17 26 28
Philenoptera nelsii --- 0 23 27 27 30 --- 4 --- 0
Cyperus palmatus 26 27 --- 0 --- 11 --- 3 --- 13
Brachiaria malacodes 11 16 --- 0 --- 14 --- 9 --- 9
Indigofera daleoides 36 31 --- 14 --- 1 --- 2 --- 0
Kohautia caespitosa subsp. brachyloba 11 17 --- 2 22 24 --- 3 --- 6
Vachellia hebeclada subsp. hebeclada --- 5 --- 13 31 30 --- 5 --- 0
Euphorbia inaequilatera --- 9 --- 0 21 24 --- 7 --- 16
Ruelliopsis damarensis --- 11 --- 4 --- 15 --- 9 --- 13
Talinum arnotii --- 3 --- 7 39 32 --- 6 --- 0
Sporobolus fimbriatus --- 2 16 20 --- 8 --- 11 --- 9
Tinnea rhodesiana 19 16 --- 0 --- 0 15 14 --- 3
Senegalia hereroensis 15 22 --- 0 --- 1 --- 4 31 31
Ipomoea bolusiana --- 4 --- 16 --- 7 --- 12 --- 3
Peliostomum leucorrhizum --- 1 --- 0 35 27 --- 12 --- 0
Hermannia quartiniana --- 5 --- 13 --- 6 --- 10 --- 16
Aristida meridionalis 31 26 --- 14 --- 0 --- 2 --- 0
Pechuel-Loeschea leubnitziae --- 5 --- 11 11 15 --- 8 --- 6
Antiphiona pinnatisecta 12 17 --- 5 --- 0 --- 6 20 22
Monechma divaricatum --- 1 --- 5 --- 7 21 17 --- 3
Achyranthes aspera var. sicula --- 8 --- 0 13 17 --- 7 --- 16
Dicoma tomentosa --- 3 --- 9 15 18 --- 7 --- 9
Solanum delagoense --- 3 --- 5 --- 8 15 14 --- 3
Ipomoea sinensis --- 5 --- 0 30 23 --- 8 --- 0
Tribulus terrestris --- 1 --- 0 25 20 --- 11 --- 3
Bidens biternata --- 6 --- 2 --- 6 --- 8 34 31
Bulbostylis hispidula 10 14 --- 7 --- 11 --- 3 --- 6
Hermbstaedtia odorata 22 19 --- 4 --- 4 --- 5 --- 6
Helinus integrifolius --- 8 --- 0 26 21 --- 6 --- 3
Hypoestes forskaolii --- 0 --- 0 --- 7 14 15 --- 16
Setaria verticillata --- 8 --- 0 11 14 --- 7 --- 13
Chloris virgata --- 9 --- 0 26 20 --- 6 --- 0
Petalidium englerianum --- 2 --- 0 --- 6 20 15 --- 6
Aloe zebrina 9 13 --- 13 --- 0 --- 6 --- 9

Overview of the Thornbush savannah – Karst tran­sition syntaxa:

3.1 Undefined upper hierarchy

3.1.1.1 Combreto hereroense-Tarchonanthoetum camphorate

3.1.1.2 Aristido pilgeri-Vachellietum eriolobae

3.1.1.3 Cenchro ciliaris-Senegalietum detinentis

3.1.1.3.1 Cenchro ciliaris-Senegalietum detinentis typicum

3.1.1.3.2 Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae

3.1.1.4 Eucleo undulatae-Oleetum africanae

3.1.1.1 Combreto hereroense-Tarchonanthoetum camphorati ass. nov.

Number of relevés: 93

Number of species observed: 226

Estimated number of species: 368

Average species density in 1000 m2: 48

Type relevé: 4318 (holotypus), sampled on 19 March 1997 at 19.69361°S, 18.05528°E (John Pandeni Research Station / Gressenhof)

Combretum hereroense (s1) 5%, Tarchonanthus camphoratus (s1) 5%, Senegalia mellifera subp. detinens (s1) 2%, Senegalia cinerea (s1) 0.1%, Ziziphus mucronata (s1) 0.1%, Grewia flava (s2) 1%, Dichrostachys cinerea (s2) 0.3%, Euclea undulata (s2) 0.3%, Ozoroa paniculosa (s2) 0.3%, Searsia ciliata (s2) 0.3%, Grewia bicolor (s2) 0.1%, Lantana angolensis (s2) 0.1%, Anthephora pubescens (gp) 1%, Aristida congesta subsp. congesta (gp) 1%, Brachiaria nigropedata (gp) 1%, Schmidtia pappophoroides (gp) 1%, Andropogon gayanus (gp) 0.3%, Cymbopogon pospischilii (gp) 0.3%, Fingerhuthia africana (gp) 0.3%, Heteropogon contortus (gp) 0.3%, Panicum coloratum (gp) 0.3%, Pogonarthria squarrosa (gp) 0.3%, Stipagrostis uniplumis var. uniplumis (gp) 0.3%, Aristida rhiniochloa (ga) 60%, Pogonarthria fleckii (ga) 2%, Urochloa brachyura (ga) 1%, Aristida adscensionis (ga) 0.3%, Aristida effusa (ga) 0.3%, Aristida stipoides (ga) 0.3%, Tragus berteronianus (ga) 0.3%, Tragus racemosus (ga) 0.3%, Triraphis purpurea (ga) 0.3%, Eustachys paspaloides (ga) 0.1%, Indigofera charlieriana (hl) 1%, Bulbostylis hispidula (hl) 0.3%, Cyperus palmatus (hl) 0.3%, Dicoma anomala (hl) 0.3%, Hermannia tomentosa (hl) 0.3%, Indigofera pechuelii (hl) 0.3%, Kyphocarpa angustifolia (hl) 0.3%, Limeum sulcatum (hl) 0.3%, Melhania virescens (hl) 0.3%, Otoptera burchellii (hl) 0.3%, Rotheca myricoides (hl) 0.3%, Seddera suffruticosa (hl) 0.3%, Sesamum triphyllum (hl) 0.3%, Acalypha segetalis (hl) 0.1%, Aptosimum decumbens (hl) 0.1%, Euphorbia inaequilatera (hl) 0.1%, Geigeria ornativa (hl) 0.1%, Hibiscus caesius (hl) 0.1%, Pentarrhinum insipidum (hl) 0.1%, Trochomeria macrocarpa subsp. vitifolia (hl) 0.1%

Diagnostic species: Brachiaria nigropedata, Anthe­phora pubescens, Sesamum triphyllum, Rotheca myricoides, Schmidtia pappophoroides, Vernonia fastigiata, Dicoma anomala, Ozoroa paniculosa, Tragus racemosus, Triraphis purpurea, Indigofera charlieriana, Indigofera pechuelii

Constant species: Senegalia mellifera subsp. detinens, Tarchonanthus camphoratus, Combretum hereroense, Hetero­pogon contortus, Dichrostachys cinerea, Stipa­gros­tis uniplumis var. uniplumis, Fingerhuthia africana, Gre­wia flava, Seddera suffruticosa, Melinis repens subsp. grandiflora, Combretum imberbe, Eragrostis trichophora, Aristida rhiniochloa, Urochloa brachyura, Melhania vires­cens, Euclea undulata, Enneapogon scoparius

The Combreto hereroense-Tarchonanthoetum camphorati forms an extensive low bushland to tall shrubland south of Grootfontein towards the Omuramba Omatako (Figures 8a, 9a). These bushlands are dominated by the phanerophytes Tarchonanthus camphoratus, Senegalia mellifera subsp. detinens, Combretum hereroense, Euclea undulata, Dichrostachys cinerea, Croton gratissimus, Combretum imberbe, Combretum apiculatum and Catophractes alexandri. The grass layer is dominated by Aristida rhiniochloa, Stipagrostis uniplumis var. uniplumis, Schmidtia pappophoroides, Enneapogon scoparius, Aristida adscensionis, Pogonarthria fleckii, Urochloa oligotricha, Trachypogon spicatus, Fingerhuthia africana and Aristida congesta subsp. congesta. Schmidtia pappophoroides, Brachiaria nigropedata, Fingerhuthia africana and Anthephora pubescens form the palatable climax grasses of this association.

This association occurs on shallow to moderately deep, medium-textured soils (often Leptsols) over calcrete, as part of lower Kalahari deposits (Coetzee et al. 1998). These are underlain by the ancient Grootfontein Metamorphic Complex (Geological Survey 1980; South African Committee for Stratigraphy 1980; Kamona and Günzel 2007). The calcrete is often evident as gravel (up to 40%) on the surface, with occasional small, medium and large calcrete stones visible on the surface. Although the topography is generally flat with less than 2° slope, the altitude ranges between 1170 and 1850 m a.s.l.

Figure 8. 

Typical structure of the associations of the Thornbush – Karstveld transition: (a) Combreto hereroense-Tarchonanthoetum camphorati; (b) Aristido pilgeri-Vachellietum eriolobae; (c) Cenchro ciliaris-Senegalietum detinentis typicum; (d) Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae; (e) Eucleo undulatae-Oleetum africanae.

Figure 9. 

Typical views of the associations of the Thornbush – Karstveld transition: (a) Combreto hereroense-Tarchonanthoetum camphorati, relevé 7987; (b) Aristido pilgeri-Vachellietum eriolobae, relevé 7804; (c) Cenchro ciliaris-Senegalietum detinentis typicum, relevé 3534; (d) Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae, relevé 3521; (e) The Cenchro ciliaris-Senegalietum detinentis can degrade to this badly encroached state, relevé 7823; (f) Eucleo undulatae-Oleetum africanae, relevé 8001.

3.1.1.2 Aristido pilgeri-Vachellietum eriolobae ass. nov.

Number of relevés: 55

Number of species observed: 155

Estimated number of species: 292

Average species density in 1000 m2: 32

Type relevé: 7803 (holotypus), sampled on 26 April 2007 at 19.93222°S, 17.96028°E (Omambonde Tal)

Vachellia erioloba (t2) 10%, Vachellia luederitzii (t3) 2%, Philenoptera nelsii (t3) 1%, Senegalia mellifera subsp. melli­fera (s1) 20%, Dichrostachys cinerea (s1) 5%, Grewia flava (s1) 5%, Senegalia cinerea (s1) 5%, Grewia bicolor (s1) 2%, Grewia flavescens (s1) 2%, Combretum hereroense (s1) 1%, Ehretia rigida (s1) 0.4%, Tarchonanthus camphoratus (s1) 0.4%, Pechuel-Loeschea leubnitziae (s2) 1%, Asparagus nelsii (s2) 0.4%, Commiphora angolensis (s2) 0.4%, Lantana angolensis (s2) 0.4%, Stipagrostis uniplumis var. uniplumis (gp) 40%, Aristida pilgeri (gp) 5%, Eragrostis rigidior (gp) 5%, Pogonarthria squarrosa (gp) 0.4%, Melinis repens subsp. grandiflora (ga) 1%, Urochloa brachyura (ga) 0.4%, Hermannia eenii (hl) 5%, Aptosimum angustifolium (hl) 1%, Hibiscus caesius (hl) 0.4%, Kyphocarpa angustifolia (hl) 0.4%, Melhania acuminata (hl) 0.4%, Nidorella resedifolia (hl) 0.4%, Otoptera burchellii (hl) 0.4%, Phyllanthus pentandrus (hl) 0.4%, Polydora steetziana (hl) 0.4%, Rhynchosia totta (hl) 0.4%, Seddera suffruticosa (hl) 0.4%, Waltheria indica (hl) 0.4%

Diagnostic species: Hermannia eenii, Aristida pilgeri, Melhania acuminata, Vachellia erioloba, Terminalia sericea, Senegalia cinerea, Dicoma schinzii, Waltheria indica, Digitaria seriata

Constant species: Senegalia mellifera subsp. detinens, Dichrostachys cinerea, Stipagrostis uniplumis var. uniplumis, Vachellia reficiens / luederitzii, Grewia flava

The Aristido pilgeri-Vachellietum eriolobae is mainly found near riverine systems through sandy substrate. Typical is the floodplain valley of the Omambonde Omatako along the southern edge of the study area, but also the Ugab headwaters south-west of Otavi and to the north and east of the Omuramba Ovambo between Maroelaboom and Oshivelo. The structure is typically a moderately closed tall bushland dominated by Senegalia mellifera subsp. detinens, Terminalia sericea, Peltophorum africanum, Vachellia erioloba, Senegalia cinerea, Dichrostachys cinerea, Vachellia reficiens / luederitzii and Philenoptera nelsii. In the grass layer, Stipagrostis uniplumis var. uniplumis, Eragrostis trichophora, Eragrostis rigidior, Eragrostis rotifer, Eragrostis lehmanniana, Aristida congesta subsp. congesta, Schmidtia pappophoroides and Pogonarthria fleckii dominate (Figures 8b, 9b).

Strohbach (2002) described an Acacia erioloba-Stipagrostis uniplumis association which resembles the Aristido pilgeri-Vachellietum eriolobae. According to her, the soils are generally loamy sands or occasionally sandy loams overlying the Omingonde formation. The topography is generally flat (< 2° slope), on altitudes between 1200 and 1500 m a.s.l. The Aristido pilgeri-Vachellietum eriolobae is related to the Schmidtio kalahariensis-Vachellietum eriolobae described by Strohbach (2021; see also Strohbach et al. 2019) as well as to the Stella Bushveld and the Kimberly Thornveld in the Savanna Biome of South Africa (Mucina and Rutherford 2006). Yet the species composition is distinctly different from these.

3.1.1.3 Cenchro ciliaris-Senegalietum detinentis ass. nov.

Number of relevés: 216

Number of species observed: 323

Estimated number of species: 490

Average species density in 1000 m2: 44

Type relevé: 3330 (holotypus), sampled on 14 March 2002 at 19.85778°S, 17.42083°E (Okoruso)

Senegalia mellifera subsp. detinens (s1) 5%, Vachellia reficiens (s1) 5%, Ziziphus mucronata (s1) 0.5%, Lycium bosciifolium (s1) 0.2%, Grewia flava (s1) 0.1%, Pechuel-Loeschea leubnitziae (s2) 0.5%, Hibiscus calyphyllus (s2) 0.2%, Ziziphus mucronata (s2) 0.2%, Aizoon virgatum (s2) 0.1%, Asparagus cooperi (s2) 0.1%, Ehretia rigida (s2) 0.1%, Heliotropium nelsonii (s2) 0.1%, Leucosphaera bainesii (s2) 0.1%, Ptycholobium biflorum (s2) 0.1%, Solanum lichtensteinii (s2) 0.1%, Tarchonanthus camphoratus (s2) 0.1%, Eragrostis trichophora (gp) 25%, Cenchrus ciliaris (gp) 20%, Eragrostis echinochloidea (gp) 1%, Eragrostis rotifer (gp) 0.1%, Urochloa oligotricha (ga) 5%, Aristida adscensionis (ga) 0.1%, Aristida effusa (ga) 0.1%, Eragrostis porosa (ga) 0.1%, Melinis repens subsp. grandiflora (ga) 0.1%, Tragus berteronianus (ga) 0.1%, Nidorella resedifolia (hl) 0.5%, Cucumis anguria (hl) 0.2%, Ocimum filamentosum (hl) 0.2%, Commicarpus pentandrus (hl) 0.1%, Corchorus tridens (hl) 0.1%, Gomphrena celosioides (hl) 0.1%, Hibiscus palmatus (hl) 0.1%, Indigastrum costatum (hl) 0.1%, Ipomoea obscura var. obscura (hl) 0.1%, Ipomoea sinensis (hl) 0.1%, Ocimum americanum var. americanum (hl) 0.1%, Osteospermum muricatum subsp. muricatum (hl) 0.1%, Phyllanthus maderaspatensis (hl) 0.1%, Rhynchosia minima (hl) 0.1%, Ruellia species (hl) 0.1%, Senna italica (hl) 0.1%, Tribulus terrestris (hl) 0.1%

Diagnostic species: Corchorus tridens

Constant species: Senegalia mellifera subsp. deti­nens, Dichrostachys cinerea, Vachellia reficiens / luede­ritzii, Grewia flava, Melhania virescens, Cenchrus ciliaris, Eragrostis trichophora, Eragrostis echinochloidea

The Cenchro ciliaris-Senegalietum detinentis forms the relatively dense bushlands south of the Otavi Mountain range, roughly covering the triangle Rietfontein – Otavi – Otjiwarongo. The association occurs on the flat to undulating landscapes formed by the marbles and schists of the Swakop Group (Geological Survey 1980; South African Committee for Stratigraphy 1980; Schneider 2004; Kamona and Günzel 2007). While Strohbach (2002) recognised two separate communities (Acacia mellifera - Cenchrus ciliaris community and the Acacia mellifera - Stipagrostis hirtigluma community, respectively), due to their very similar composition and structure, these are recognised here as subassociations of the Cenchro ciliaris-Senegalietum detinentis.

3.1.1.3.1 Cenchro ciliaris-Senegalietum detinentis typicum subass. nov.

Number of relevés: 71

Number of species observed: 216

Estimated number of species: 324

Average species density in 1000 m2: 46

Diagnostic species: Corchorus tridens, Heliotropium nelsonii, Leucosphaera bainesii, Monechma genistifolium, Ipomoea obscura var. obscura, Asparagus cooperi, Eragrostis porosa, Solanum tettense var. renschii, Hibiscus calyphyllus, Geigeria acaulis, Boscia albitrunca, Hibiscus palmatus, Ptycholobium biflorum subsp. angolensis

Constant species: Vachellia reficiens / luederitzii, Sene­galia mellifera subsp. detinens, Eragrostis trichophora, Dichrostachys cinerea, Cenchrus ciliaris, Grewia flava

Strohbach (2002) described this subassociation as her Acacia mellifera - Cenchrus cilliaris association. Typically, the Cenchro ciliaris-Senegalietum detinentis typicum forms a moderately closed tall shrubland or short bushland, depending on the density of trees in the stand (Figures 8c, 9c). The vegetation is described by Strohbach (2002) as less encroached with a more prominent perennial grass sward than the Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae. The phanerophytic layer is dominated by Senegalia mellifera subsp. detinens, Vachellia reficiens / luederitzii, Dichrostachys cinerea and Grewia species, with occasionally also Philenoptera nelsii, Vachellia tortilis subsp. heteracantha, Tarchonanthus camphoratus and Croton gratissimus also occurring. The grass sward is dominated by Eragrostis trichophora, Cenchrus ciliaris, Eragrostis rigidior, Eragrostis porosa, Enneapogon cenchroides, Stipagrostis uniplumis var. uniplumis and Sporobolus fimbriatus.

The Cenchro ciliaris-Senegalietum detinentis typicum occurs on deeper sandy loams and sandy clay loams, mostly Chromic Cambisols. There has only limited stone cover recorded on single relevés. The subassociation occurs on flat to gently undulating slopes at an altitudinal range of between 1170 and 1550 m a.s.l.

3.1.1.3.2 Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae subass. nov.

Number of relevés: 145

Number of species observed: 254

Estimated number of species: 431

Average species density in 1000 m2: 43

Type relevé: 3521 (holotypus), sampled on 25 April 2002 at 20.05667°S, 17.04750°E (Gerhardtshausen / Felsenquelle)

Peltophorum africanum (t3) 5%, Senegalia mellifera subsp. detinens (s1) 40%, Croton gratissimus var. gratissimus (s1) 10%, Dichrostachys cinerea (s1) 5%, Vachellia reficiens (s1) 5%, Grewia flava (s1) 2%, Tarchonanthus camphoratus (s1) 2%, Terminalia prunioides (s1) 2%, Catophractes alexandri (s1) 1%, Combretum hereroense (s1) 0.5%, Euclea undulata (s1) 0.5%, Searsia marlothii (s1) 0.2%, Ehretia rigida (s2) 0.5%, Hypoestes forskaolii (s2) 0.5%, Melhania virescens (s2) 0.5%, Aizoon virgatum (s2) 0.2%, Lantana angolensis (s2) 0.2%, Mundulea sericea (s2) 0.2%, Seddera suffruticosa (s2) 0.2%, Boscia foetida subsp. foetida (s2) 0.1%, Chascanum pinnatifidum (s2) 0.1%, Commiphora pyracanthoides (s2) 0.1%, Helichrysum tomentosulum (s2) 0.1%, Hibiscus caesius (s2) 0.1%, Enneapogon scoparius (gp) 5%, Eragrostis echinochloidea (gp) 5%, Heteropogon contortus (gp) 2%, Cenchrus ciliaris (gp) 0.5%, Fingerhuthia africana (gp) 0.5%, Dichanthium annulatum var. papillosum (gp) 0.2%, Stipagrostis hirtigluma (ga) 15%, Indigofera charlieriana (hl) 0.1%, Ocimum americanum var. americanum (hl) 0.1%, Sericorema sericea (hl) 0.1%

Constant species: Senegalia mellifera subsp. detinens, Combretum hereroense, Grewia flava, Dichrostachys cinerea, Melhania virescens, Vachellia reficiens / luederitzii, Eragrostis echinochloidea, Tarchonanthus camphoratus

Strohbach (2002) described this subassociation as her Acacia mellifera - Stipagrostis hirtigluma community. Typically, the Cenchro ciliaris-Senegalietum detinentis stipagrostietosum hirtiglumae forms a closed tall shrubland, dominated by the phanerophytes Senegalia mellifera subsp. detinens, Vachellia reficiens / luederitzii, Dichrostachys cinerea, Terminalia prunioides, Tarchonanthus camphoratus, Croton gratissimus, Combretum imberbe, Catophractes alexandri, Vachellia karroo and Combretum hereroense. The grass sward is dominated by Stipagrostis hirtigluma subsp. hirtigluma, Eragrostis trichophora, Eragrostis echinochloidea, Enneapogon scoparius, Enneapogon desvauxii, Cenchrus ciliaris, Urochloa brachyura, Stipagrostis uniplumis var. uniplumis, Sporobolus ioclados, Setaria pumila, Microchloa caffra, Melinis repens subsp. grandiflora, Hetero­pogon contortus, Eragrostis rigidior, Eragrostis porosa, Eragrostis nindensis, Eragrostis lehmanniana and Enneapogon cenchroides. Conspicuous dwarfshrubs include Petalidium englerianum, Monechma spartioides and Monechma genistifolium. The vegetation is often densely encroached with a weak grass sward (Strohbach 2002) (Figures 8d, 9d).

The soils consist of sandy loam and sandy clay loam, often mollic Leptosols or petric Calcisols (Strohbach 2002). Stone cover is more prominent, reaching up to 5% medium-sized stones. The topography is gently undulating, but some relevés have been sampled in rolling landscapes. The altitude ranges between 1160 and 1850 m a.s.l.

3.1.1.4 Eucleo undulatae - Oleetum africanae ass. nov.

Number of relevés: 32

Number of species observed: 189

Estimated number of species: 318

Type relevé: 8097 (holotypus), sampled on 15 April 2008 at 19.44583°S, 17.95917°E (Toggenberg)

Spirostachys africana (t1) 10%, Elaeodendron transvaalense (t2) 1%, Vachellia luederitzii (t3) 5%, Commiphora glandulosa (t3) 1%, Senegalia mellifera subsp. detinens (s1) 20%, Croton gratissimus var. subgratissimus (s1) 10%, Olea europaea subsp. africana (s1) 10%, Euclea undulata (s1) 5%, Searsia marlothii (s1) 2%, Terminalia prunioides (s1) 2%, Commiphora africana (s1) 1%, Commiphora glandulosa (s1) 1%, Dombeya rotundifolia (s1) 1%, Flueggea virosa (s1) 1%, Mundulea sericea (s1) 1%, Vachellia nilotica (s1) 1%, Lantana angolensis (s2) 1%, Aerva leucura (s2) 0.5%, Fingerhuthia africana (gp) 5%, Enneapogon scoparius (gp) 2%, Eragrostis echinochloidea (gp) 2%, Eragrostis rigidior (gp) 2%, Heteropogon contortus (gp) 2%, Andropogon chinensis (gp) 1%, Anthephora pubescens (gp) 1%, Cenchrus ciliaris (gp) 1%, Eragrostis nindensis (gp) 1%, Oropetium capense (gp) 1%, Urochloa oligotricha (gp) 1%, Cymbopogon pospischilii (gp) 0.5%, Digitaria eriantha (gp) 0.5%, Eustachys paspaloides (gp) 0.5%, Enneapogon cenchroides (ga) 10%, Eragrostis porosa (ga) 10%, Aristida effusa (ga) 5%, Aristida rhiniochloa (ga) 2%, Enneapogon desvauxii (ga) 2%, Melinis repens subsp. grandiflora (ga) 2%, Brachiaria malacodes (ga) 1%, Tragus racemosus (ga) 0.5%, Cyperus amabilis (hl) 2%, Blepharis obmitrata (hl) 1%, Buchnera hispida (hl) 1%, Calostephane divaricata (hl) 1%, Achyranthes aspera var. sicula (hl) 0.5%, Aptosimum lineare (hl) 0.5%, Commelina benghalensis (hl) 0.5%, Geigeria ornativa (hl) 0.5%, Heliotropium ovalifolium (hl) 0.5%, Hibiscus calyphyllus (hl) 0.5%, Indigofera charlieriana (hl) 0.5%, Kohautia aspera (hl) 0.5%, Melhania virescens (hl) 0.5%, Monechma spartioides (hl) 0.5%, Pavonia burchellii (hl) 0.5%, Pentarrhinum insipidum (hl) 0.5%, Pupalia lappacea (hl) 0.5%, Sericorema sericea (hl) 0.5%, Tagetes minuta (hl) 0.5%, Tephrosia dregeana var. dregeana (hl) 0.5%

Diagnostic species: Olea europaea subsp. africana, Fingerhuthia africana, Digitaria eriantha, Euclea undulata, Croton gratissimus, Kohautia aspera

Constant species: Senegalia mellifera subsp. detinens, Heteropogon contortus, Vachellia reficiens / luederitzii, Melhania virescens, Searsia marlothii, Combretum hereroense, Eragrostis echinochloidea, Ziziphus mucronata, Enneapogon scoparius, Lantana angolensis, Cenchrus ciliaris, Tarchonanthus camphoratus, Seddera suffruticosa, Hibiscus caesius, Grewia flava, Dichrostachys cinerea, Anthephora pubescens

The Eucleo undulatae-Oleetum africanae forms a short, moderately closed thicket dominated by the phanerophytes Senegalia mellifera subsp. detinens, Olea europaea subsp. africana, Vachellia reficiens / luederitzii, Dichrostachys cinerea, Combretum imberbe, Combretum hereroense, Euclea undulata and Catophractes alexandri. The grass sward consists of predominantly Enneapogon desvauxii, Heteropogon contortus, Urochloa oligotricha, Stipagrostis uniplumis var. uniplumis, Fingerhuthia africana, Enneapogon scoparius, Cenchrus ciliaris, Eragrostis trichophora and Eragrostis echinochloidea (Figures 8e, 9f).

This association occurs on the southern footslopes and pedeplains of the Otavi mountain range. It is especially widespread around Otavi but is found also elsewhere along the mountain range as far east as Gaikos mountain. The soils are described as medium-textured, dark Leptosols on calcretes (Coetzee et al. 1998). Stone cover consists of a mixture of gravel, small, medium and large stones (calcretes) up to 30% cover. The slopes are gently undulating to undulating, at an altitudinal range of between 1300 and 1540 m a.s.l.

4. Kalahari

Pockets of Kalahari sand deposits are found within the Otavi Mountain range, supporting vegetation typical for the Woodland savanna of the northern Kalahari sensu Giess (1998). Within the present study area, the Kalahari vegetation is dominated by the families Poaceae (57 species) and Fabaceae (54 species). All other families are represented by 15 or less species. An abbreviated synoptic table is presented in Table 4, whilst the full synoptic table is available in Suppl. material 3.

Table 4.

Abbreviated synoptic table for the Kalahari vegetation, showing all species occurring in more than 10% of relevés of this group, with fidelity (phi coefficient × 100) and frequency of occurrence (%).

Association 4.1.1.1 4.1.1.2 4.1.1.3 4.1.1.4
No of relevés 11 25 15 21
Species phi % phi % phi % phi %
Grewia olukondae 69 100 --- 28 --- 0 --- 38
Tricholaena monachne 65 55 --- 4 --- 0 --- 0
Monechma debile 62 45 --- 0 --- 0 --- 0
Schinziophyton rautanenii 56 45 --- 0 --- 7 --- 0
Pterocarpus angolensis 55 36 --- 0 --- 0 --- 0
Indigofera daleoides 51 64 --- 12 --- 20 --- 5
Phyllanthus maderaspatensis 51 64 --- 24 --- 0 --- 14
Aristida stipitata 48 91 --- 52 --- 20 --- 33
Hibiscus vitifolius 47 27 --- 0 --- 0 --- 0
Strychnos pungens 47 27 --- 0 --- 0 --- 0
Chamaecrista biensis 42 36 --- 8 --- 0 --- 5
Burkea africana 42 45 --- 12 --- 13 --- 0
Ochna pulchra 41 64 --- 32 --- 27 --- 0
Jacquemontia tamnifolia --- 9 76 80 --- 7 --- 0
Calostephane divaricata --- 0 61 44 --- 0 --- 0
Ozoroa schinzii --- 9 59 52 --- 0 --- 0
Combretum engleri --- 9 56 48 --- 0 --- 0
Phyllanthus omahakensis --- 0 55 36 --- 0 --- 0
Acanthosicyos naudinianus --- 0 54 56 --- 7 --- 14
Schmidtia kalahariensis --- 0 48 28 --- 0 --- 0
Megaloprotachne albescens --- 0 44 24 --- 0 --- 0
Polydora steetziana --- 0 42 44 --- 0 --- 24
Bauhinia petersiana subsp. macrantha --- 64 40 84 --- 40 --- 10
Grewia flavescens --- 0 --- 56 62 100 --- 29
Pavonia burchellii --- 0 --- 4 59 47 --- 0
Limeum sulcatum --- 0 --- 0 56 53 --- 14
Senegalia ataxacantha --- 36 --- 60 53 93 --- 0
Commelina benghalensis --- 0 --- 4 51 47 --- 10
Ziziphus mucronata --- 0 --- 4 50 53 --- 19
Ipomoea welwitschii --- 0 --- 0 47 33 --- 5
Chamaecrista absus --- 0 25 52 43 67 --- 10
Tarchonanthus camphoratus --- 0 --- 0 40 27 --- 5
Terminalia prunioides --- 0 --- 32 --- 13 65 86
Combretum hereroense --- 0 --- 0 --- 7 53 43
Seddera suffruticosa --- 0 --- 0 --- 0 48 29
Senegalia mellifera subsp. detinens --- 18 --- 16 --- 67 45 86
Aristida rhiniochloa --- 0 --- 12 --- 7 44 43
Hyphaene petersiana --- 9 --- 0 --- 0 43 33
Boscia albitrunca --- 0 --- 4 --- 7 41 33
Combretum collinum 45 82 57 92 --- 0 --- 0
Terminalia sericea --- 91 --- 96 --- 93 --- 67
Dichrostachys cinerea --- 55 --- 80 --- 87 29 100
Urochloa brachyura --- 55 --- 84 --- 87 --- 95
Stipagrostis uniplumis var. uniplumis --- 82 --- 80 --- 60 --- 86
Croton gratissimus 38 100 27 92 --- 47 --- 43
Combretum apiculatum --- 45 --- 60 --- 60 32 90
Senegalia cinerea --- 45 --- 68 --- 87 --- 62
Melinis repens subsp. grandiflora --- 64 30 88 --- 47 --- 52
Grewia bicolor --- 27 --- 64 --- 60 27 81
Pogonarthria fleckii --- 18 37 84 --- 27 33 81
Commiphora glandulosa --- 36 --- 64 --- 53 --- 67
Peltophorum africanum --- 36 --- 16 32 80 28 76
Eragrostis dinteri --- 55 33 68 --- 0 --- 38
Commiphora angolensis --- 9 40 64 --- 40 --- 14
Vachellia erioloba --- 18 25 52 --- 20 --- 38
Oxygonum alatum --- 18 26 52 --- 27 --- 29
Melhania acuminata --- 18 --- 20 32 60 --- 38
Grewia flava --- 0 --- 40 --- 33 --- 33
Limeum fenestratum --- 45 --- 40 --- 7 --- 24
Schmidtia pappophoroides --- 18 --- 28 --- 20 --- 43
Tephrosia dregeana var. dregeana --- 18 --- 28 --- 47 --- 24
Clerodendrum ternatum --- 18 --- 24 --- 47 --- 24
Philenoptera nelsii --- 0 --- 40 --- 33 --- 24
Eragrostis rigidior --- 0 --- 12 --- 40 35 52
Aristida adscensionis --- 36 31 48 --- 0 --- 14
Bidens biternata --- 36 --- 20 30 53 --- 10
Combretum psidioides 33 55 --- 32 --- 13 --- 14
Evolvulus alsinoides --- 9 --- 28 --- 13 27 43
Digitaria seriata --- 18 --- 36 --- 13 --- 29
Ximenia americana 35 55 --- 20 --- 7 --- 29
Rhynchosia venulosa 40 64 --- 8 --- 40 --- 14
Syncolostemon bracteosus --- 9 29 44 --- 33 --- 5
Vachellia reficiens / luederitzii --- 0 --- 24 --- 13 37 48
Sida ovata --- 27 --- 32 --- 13 --- 19
Eragrostis trichophora --- 36 --- 16 --- 7 --- 33
Searsia tenuinervis --- 36 --- 20 --- 13 --- 24
Waltheria indica --- 9 --- 12 --- 33 --- 33
Asparagus nelsii --- 0 --- 32 --- 27 --- 19
Mundulea sericea --- 27 --- 24 --- 20 --- 14
Bulbostylis hispidula --- 0 29 36 --- 13 --- 19
Xenostegia tridentata subsp. angustifolia --- 0 37 40 --- 7 --- 19
Tragus berteronianus --- 9 --- 28 --- 7 --- 24
Cyperus margaritaceus --- 27 --- 8 24 40 --- 14
Enneapogon cenchroides --- 0 34 36 --- 0 --- 24
Lantana angolensis --- 0 --- 16 --- 27 --- 29
Panicum maximum --- 36 --- 28 --- 7 --- 5
Commelina africana --- 36 --- 12 --- 27 --- 10
Albizia anthelmintica --- 0 --- 24 --- 20 --- 19
Commiphora africana --- 0 29 32 --- 7 --- 19
Tephrosia purpurea --- 0 30 32 --- 0 --- 24
Eragrostis lehmanniana --- 0 --- 28 35 40 --- 0
Dicoma tomentosa --- 0 --- 8 --- 20 34 38
Kyphocarpa angustifolia --- 9 --- 20 --- 7 --- 24
Melinis repens subsp. repens --- 27 --- 0 --- 33 --- 19
Triraphis schinzii --- 18 --- 4 --- 20 --- 29
Aristida congesta subsp. congesta --- 9 --- 12 --- 0 38 38
Phyllanthus pentandrus --- 0 --- 8 36 40 --- 19
Cyperus amabilis --- 0 --- 28 --- 13 --- 14
Cleome rubella --- 0 --- 12 --- 33 --- 19
Heteropogon melanocarpus --- 0 34 32 --- 13 --- 5
Acrotome angustifolia --- 0 37 32 --- 0 --- 14
Gisekia africana --- 0 --- 12 --- 27 --- 19
Rhynchosia totta --- 0 --- 24 --- 7 --- 19
Sporobolus panicoides --- 0 --- 12 --- 20 --- 24
Vachellia nilotica --- 0 --- 12 --- 13 --- 29
Zornia milneana --- 0 --- 12 30 33 --- 14
Aristida pilgeri --- 0 --- 0 --- 20 39 38
Blepharis obmitrata --- 27 --- 12 --- 0 --- 19
Thunbergia aurea --- 27 --- 8 25 33 --- 0
Blepharis maderaspatensis --- 27 --- 4 --- 27 --- 10
Tephrosia lupinifolia --- 9 36 32 --- 7 --- 0
Spermacoce senensis --- 0 --- 16 33 33 --- 5
Dicoma schinzii --- 9 --- 20 --- 7 --- 10
Sesamum triphyllum --- 9 24 24 --- 7 --- 5
Ximenia caffra --- 9 --- 12 33 33 --- 0
Setaria pumila --- 9 --- 0 32 33 --- 14
Spirostachys africana --- 0 --- 8 --- 13 --- 24
Monechma spartioides --- 0 --- 4 --- 20 --- 24
Combretum imberbe --- 0 --- 0 --- 20 29 29
Erlangea misera 40 36 --- 16 --- 0 --- 0
Indigofera flavicans 38 36 --- 12 --- 7 --- 0
Asparagus exuvialis --- 0 --- 16 --- 0 --- 19
Gymnosporia senegalensis --- 0 --- 0 --- 13 34 29

Overview of the Kalahari associations:

4.1 Undefined upper hierarchy

4.1.1.1 Terminalio sericeae-Schinziophyetum rautanenii

4.1.1.2 Combreto collini-Terminalietum sericeae

4.1.1.3 Senegalio cinereae-Peltophoretum africanae

4.1.1.4 Terminalietum sericeo-prunioidis

4.1.1.1 Terminalio sericeae - Schinziophyetum rautanenii B. Strohbach 2014

Number of relevés: 11

Number of species observed: 72

Estimated number of species: 106

Average species density in 1000 m2: 30

Type relevé: 4013 (holotypus), designated by Strohbach (2014). Sampled on 26 March 1992 at 19.42139°S, 18.38889°E (Gaikos).

Schinziophyton rautanenii (t1) 2a, Pterocarpus angolensis (t1) +, Burkea africana (t2) 1, Combretum collinum (t2) +, Lannea discolor (t2) r, Peltophorum africanum (t3) +, Croton gratissimus var. gratissimus (s1) 2b, Terminalia sericea (s1) 2b, Bauhinia petersiana subsp. macrantha (s1) +, Grewia olukondae (s1) +, Ochna pulchra (s2) +, Strychnos pungens (s2) r, Eragrostis trichophora (gp) 1, Melinis repens subsp. repens (gp) +, Panicum maximum (gp) +, Stipagrostis uniplumis var. uniplumis (gp) +, Aristida stipitata subsp. stipi­tata (ga) 3, Melinis repens subsp. grandiflora (ga) +, Tricholaena monachne (ga) +, Erlangea misera (hl) 1, Bidens biternata (hl) +, Blepharis obmitrata (hl) +, Cyperus margaritaceus (hl) +, Hibiscus vitifolius (hl) +, Hypoestes forskaolii (hl) +, Indigofera daleoides (hl) +, Indigofera flavicans (hl) +, Monechma debile (hl) +, Phyllanthus maderaspatensis (hl) +, Rhynchosia sublobata (hl) +, Sida ovata (hl) +, Tephrosia dregeana var. dregeana (hl) +, Thunbergia aurea (hl) +

Diagnostic species: Grewia olukondae, Tricholaena monachne, Monechma debile, Schinziophyton rautanenii, Pterocarpus angolensis, Indigofera daleoides, Phyllanthus maderaspatensis, Aristida stipitata, Strychnos pungens, Hibiscus vitifolius, Combretum collinum, Chamaecrista biensis, Burkea africana, Ochna pulchra

Constant species: Croton gratissimus, Terminalia sericea, Stipagrostis uniplumis var. uniplumis, Rhynchosia venulosa, Melinis repens subsp. grandiflora, Bauhinia petersiana subsp. macrantha

The Terminalio sericeae-Schinziophyetum rautanenii forms a tall, moderately closed woodland dominated by Terminalia sericea, Combretum apiculatum, Senegalia cinerea, Pterocarpus angolensis, Croton gratissimus, Combretum collinum and Schinziophyton rautanenii. The grass sward is not well developed, featuring Aristida stipitata, Stipagrostis uniplumis var. uniplumis and Melinis repens subsp. grandiflora. Other than the conspicuous presence of the tall tree species Pterocarpus angolensis and Schinziophyton rautanenii, the composition resembles that of the Combreto collini-Terminalietum sericeae (Figure 10a).

The Terminalio sericeae-Schinziophyetum rautanenii has especially been found on east-facing sand ramps of aeolian origin (Lancaster and Tchakerian 1996; Rowell et al. 2017) in the Gaikos and Kokasib mountains north-east of Grootfontein. The topography is gently undulating with no stone cover, at an altitudinal range of between 1190 and 1350 m a.s.l.

4.1.1.2 Combreto collini - Terminalietum sericeae B. Stroh­bach 2014

Number of relevés: 25

Number of species observed: 127

Estimated number of species: 213

Average species density in 1000 m2: 41

Diagnostic species: Jacquemontia tamnifolia, Calostephane divaricata, Ozoroa schinzii, Combretum collinum, Combretum engleri, Phyllanthus omahakensis, Acanthosicyos naudinianus, Schmidtia kalahariensis, Megalo­protachne albescens, Polydora steetziana, Bauhinia petersiana subsp. macrantha

Constant species: Terminalia sericea, Croton gratissimus, Melinis repens subsp. grandiflora, Urochloa brachyura, Pogonarthria fleckii, Stipagrostis uniplumis var. uniplumis, Dichrostachys cinerea, Senegalia cinerea, Eragrostis dinteri, Grewia bicolor, Commiphora glandulosa, Commiphora angolensis

The Combreto collini-Terminalietum sericeae forms a short, moderately closed bushland dominated by the phanero­phytes Terminalia sericea, Croton gratissimus, Bauhinia petersiana subsp. macrantha, Combretum psidioides, Combretum collinum and Grewia olukondae. The grass sward is dominated by Aristida stipitata, Schmidtia kalahariensis, Megalo­protachne albescens, Eragrostis trichophora, Pogonarthria fleckii, Melinis repens subsp. grandiflora, Eragrostis rigidior and Eragrostis dinteri, with Polydora steetziana a conspicuous annual herb in the matrix (Figures 10b, 11a).

Figure 10. 

Typical structure of the associations of the Kalahari habitats included in the Karstveld: (a) Terminalio sericeae-Schinziophyetum rautanenii; (b) Combreto collini-Terminalietum sericeae; (c) Senegalio cinereae-Peltophoretum africanae; (d) Terminalietum sericeo-prunioidis.

Figure 11. 

Typical views of the associations of the Kalahari habitats included in the Karstveld: (a) Combreto collini-Terminalietum sericeae, relevé 8120; (b) Senegalio cinereae-Peltophoretum africanae, relevé 7999; (c) Terminalietum sericeo-prunioidis, relevé 2783.

The Combreto collini-Terminalietum sericeae occurs on the Kalahari dune belt east and north of the Omuramba Ovambo. The presence of Combretum apiculatum, Vachellia tortilis subsp. heteracantha and Terminalia prunioides indicates the proximity to true Karstveld vegetation. This could possibly result in the recognition of a further subassociation of this very wide-spread association (cf. Strohbach 2014a) during a future review of the Kalahari types. The topo­graphy is gently undulating dune field with no stone cover, with an altitudinal range of between 1100 and 1300 m a.s.l.

4.1.1.3 Senegalio cinereae - Peltophoretum africanae ass. nov.

Number of relevés: 15

Number of species observed: 141

Estimated number of species: 244

Average species density in 1000 m2: 40

Type relevé: 8000 (holotypus), sampled on 12 March 2008 at 19.55588°S, 17.14389°E (Gobas Pforte)

Combretum imberbe (t3) 5%, Commiphora tenuipetiolata (t3) 1%, Terminalia sericea (t2) 20%, Combretum apiculatum subsp. apiculatum (t2) 5%, Spirostachys africana (t2) 2%, Pavetta zeyheri (s2) 0.5%, Dichrostachys cinerea (s1) 10%, Grewia flavescens (s1) 10%, Senegalia ataxacantha (s1) 10%, Senegalia cinerea (s1) 10%, Grewia bicolor (s1) 5%, Peltophorum africanum (s1) 5%, Rhigozum brevispinosum (s1) 2%, Ziziphus mucronata (s1) 2%, Senegalia mellifera subsp. detinens (s1) 1%, Commiphora angolensis (s1) 0.5%, Croton gratissimus var. subgratissimus (s1) 0.5%, Eragrostis lehmanniana var. lehmanniana (gp) 1%, Eragrostis porosa (ga) 10%, Setaria pumila (ga) 10%, Urochloa brachyura (ga) 10%, Tragus racemosus (ga) 2%, Brachiaria deflexa (ga) 1%, Aristida stipoides (ga) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Spermacoce senensis (hl) 5%, Achyranthes aspera var. sicula (hl) 2%, Bidens biternata (hl) 2%, Chamaecrista absus (hl) 1%, Ipomoea sinensis (hl) 1%, Cleome rubella (hl) 0.5%, Crassocephalum coeruleum (hl) 0.5%, Cyperus amabilis (hl) 0.5%, Erucastrum arabicum (hl) 0.5%, Euphorbia inaequilatera (hl) 0.5%, Gisekia africana (hl) 0.5%, Limeum sulcatum (hl) 0.5%, Melhania acuminata (hl) 0.5%, Pavonia burchellii (hl) 0.5%, Phyllanthus pentandrus (hl) 0.5%, Sesamum triphyllum (hl) 0.5%, Solanum lichtensteinii (hl) 0.5%, Zornia milneana (hl) 0.5%

Diagnostic species: Grewia flavescens, Pavonia burchellii, Limeum sulcatum, Senegalia ataxacantha, Commelina benghalensis, Ziziphus mucronata, Ipomoea welwitschii, Chamaecrista absus, Tarchonanthus camphoratus

Constant species: Terminalia sericea, Urochloa brachyura, Senegalia cinerea, Dichrostachys cinerea, Peltophorum africanum, Senegalia mellifera subsp. detinens

The Senegalio cinereae-Peltophoretum africanae forms a tall, moderately closed to closed thicket, dominated by the phanerophytes Terminalia sericea, Senegalia cinerea, Senegalia ataxacantha, Peltophorum africanum, Dichrostachys cinerea, Croton gratissimus and Combretum apiculatum. These are accompanied by the grasses Urochloa brachyura, Setaria pumila and Eragrostis rigidior (Figures 10c, 11b). Conspicuous is the mix of psammophilous species (Terminalia sericea, Senegalia ataxacantha), species preferring a loamier habitat (Senegalia cinerea, Peltophorum africanum) and species known for their preference of stony or rocky habitats (Combretum apiculatum). This is indicative of the habitat of the Senegalio cinereae-Peltophoretum africanae, being sand deposits within the Otavi mountain range. The soils consist of loose aeolian sand, are variably deep, over a rocky substrate of limestone or dolomite of the Otavi Group. Stone cover is low, with no gravel, up to 2% small, medium and large stones, but up to 40% rocks (see Figure 11c). As with most Kalahari deposits, the slopes are gently undulating, seldom rolling. The association occurs at an altitudinal range of between 1200 and 1500 m a.s.l.

4.1.1.4 Terminalietum sericeo - prunioidis ass. nov.

Number of relevés: 21

Number of species observed: 157

Estimated number of species: 273

Average species density in 1000 m2: 38

Type relevé: 8131 (holotypus), sampled on 18 April 2008 at 18.80028°S, 17.88139°E (Rushof)

Terminalia prunioides (t2) 10%, Hyphaene petersiana (t2) 5%, Vachellia erioloba (t2) 2%, Spirostachys africana (t2) 1%, Combretum apiculatum subsp. apiculatum (t3) 10%, Combretum imberbe (t3) 2%, Commiphora glandulosa (t3) 2%, Terminalia sericea (t3) 1%, Vachellia luederitzii (t3) 1%, Senegalia mellifera subsp. detinens (s2) 1%, Grewia bicolor (s1) 10%, Combretum hereroense (s1) 5%, Grewia flavescens (s1) 5%, Ximenia americana (s1) 2%, Croton gratissimus var. subgratissimus (s1) 1%, Dichrostachys cinerea (s1) 1%, Elaeodendron transvaalense (s1) 1%, Hyphaene petersiana (s1) 1%, Peltophorum africanum (s1) 1%, Ziziphus mucronata (s2) 0.5%, Eragrostis rigidior (gp) 2%, Stipagrostis uniplumis var. uniplumis (gp) 2%, Triraphis schinzii (gp) 1%, Brachiaria nigropedata (gp) 0.5%, Fingerhuthia africana (gp) 0.5%, Heteropogon contortus (gp) 0.5%, Schizachyrium sanguineum (gp) 0.5%, Schmidtia pappophoroides (gp) 0.5%, Pogonarthria fleckii (ga) 10%, Aristida rhiniochloa (ga) 2%, Eragrostis dinteri (ga) 2%, Aristida effusa (ga) 0.5%, Enneapogon cenchroides (ga) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Urochloa brachyura (ga) 0.5%, Polydora steetziana (hl) 10%, Monechma spartioides (hl) 5%, Ocimum americanum var. americanum (hl) 5%, Cyperus amabilis (hl) 1%, Waltheria indica (hl) 1%, Acrotome angustifolia (hl) 0.5%, Aptosimum decumbens (hl) 0.5%, Blepharis obmitrata (hl) 0.5%, Dicoma tomentosa (hl) 0.5%, Evolvulus alsinoides (hl) 0.5%, Geigeria ornativa (hl) 0.5%, Gymnema sylvestre (hl) 0.5%, Heliotropium nelsonii (hl) 0.5%, Hermannia eenii (hl) 0.5%, Hibiscus caesius (hl) 0.5%, Kyllinga alata (hl) 0.5%, Kyphocarpa angustifolia (hl) 0.5%, Melhania acuminata (hl) 0.5%, Ocimum filamentosum (hl) 0.5%, Seddera suffruticosa (hl) 0.5%, Sida ovata (hl) 0.5%, Tephrosia purpurea (hl) 0.5%, Zornia milneana (hl) 0.5%.

Diagnostic species: Terminalia prunioides, Combretum hereroense, Seddera suffruticosa, Senegalia mellifera subsp. detinens, Aristida rhiniochloa, Hyphaene petersiana, Boscia albitrunca

Constant species: Dichrostachys cinerea, Urochloa bra­chyura, Combretum apiculatum, Stipagrostis uni­plumis var. uniplumis, Pogonarthria fleckii, Grewia bicolor, Peltophorum africanum, Terminalia sericea, Commiphora glandulosa, Senegalia cinerea

The Terminalietum sericeo-prunioidis forms a short, moderately closed bushland. It is dominated by the phanero­phytes Combretum apiculatum, Dichrostachys cinerea and Terminalia prunioides, with Stipagrostis uniplumis var. uniplumis, Eragrostis rigidior and Aristida pilgeri forming the grass sward (Figures 10d, 11c). The unique combination of Terminalia sericea and Terminalia prunioides occurring together in the same stand is indicative of the habitat: the Terminalietum sericeo-prunioidis occurs on sandy flood plains adjacent to the Omuramba Ovambo, mostly on the western and southern sides of the Omuramba. The topography is flat and the altitude ranges from 1160 to 1500 m a.s.l.

5. The Karstveld proper: Terminalietea prunioidis cl. nov

Synopsis:

Number of relevés: 330

Holotypus: Terminalietalia prunioidis B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 640

Diagnostic species: Terminalia prunioides, Spirostachys af­ricana, Combretum apiculatum, Vachellia nilotica, Grewia villosa, Grewia bicolor

Constant species: Dichrostachys cinerea, Senegalia melli­fera subsp. detinens, Commiphora glandulosa, Melinis re­pens subsp. grandiflora, Urochloa brachyura, Croton gratissimus, Grewia flavescens, Combretum imberbe

The Karstveld sensu Giess (1998) is recognised as a vegetation class, dominated by trees and tall shrubs of Terminalia prunioides. The designated type for this class are the Terminalietalia prunioidis, representing the Karstveld plains to the north and west of the Otavi mountain range. A second order, the Commiphoro glaucescentis-Kirki­etalia acuminatae (see below), is also recognised within this class. The vegetation is dominated by the plant families Poaceae (102 species), Fabaceae (76 species) and Asteraceae (36 species). An abbreviated synoptic table is presented in Table 5, whilst the full synoptic table is available in Suppl. material 3.

Table 5.

Abbreviated synoptic table for the Terminalietea prunioidis, showing all species occurring in more than 10% of relevés of the class, with fidelity (phi coefficient × 100) and frequency of occurrence (%).

Order 5.1 Commiphoro glaucescentis- Kirkietalia acuminatae 5.2 Terminalietalia prunioidis
Alliance 5.1.1 Commiphoro glaucescentis- Kirkion acuminatae 5.2.1 5.2.2 Terminalio prunioidis-Hyphaenion petersianae 5.2.3 Dichrostachyo cinereae-Terminalion prunioidis
Association 5.1.1.1 5.1.1.2 5.1.1.3 5.2.1.1 5.2.1.2 5.2.2.1 5.2.3.1 5.2.3.2
No of relevés 18 15 21 34 49 78 71 98
Species phi % phi % phi % phi % phi % phi % phi % phi %
Vangueria infausta 75 61 --- 0 --- 0 --- 0 --- 2 --- 0 --- 0 --- 0
Pellaea calomelanos 68 50 --- 0 --- 0 --- 0 --- 0 --- 0 --- 0 --- 0
Cheilanthes dinteri 65 61 --- 7 --- 10 --- 0 --- 2 --- 0 --- 0 --- 0
Lannea discolor 59 78 9 27 15 33 --- 0 --- 2 --- 1 --- 0 --- 1
Cleome monophylla 55 39 --- 0 --- 0 --- 0 --- 0 --- 0 --- 1 --- 4
Macrotyloma axillare 51 33 --- 0 --- 0 --- 0 --- 0 --- 0 --- 3 --- 2
Ozoroa insignis 48 72 --- 7 --- 29 --- 9 7 29 --- 6 --- 10 --- 7
Andropogon gayanus var. polycladus 46 28 --- 0 --- 0 --- 0 --- 0 --- 1 --- 3 --- 0
Merremia pinnata 43 22 --- 0 --- 0 --- 0 --- 0 --- 1 --- 0 --- 0
Ipomoea verbascoidea 43 39 --- 13 --- 5 --- 0 --- 0 --- 0 --- 0 --- 8
Thunbergia aurea 41 39 16 20 --- 0 --- 0 --- 0 --- 1 --- 6 --- 2
Danthoniopsis dinteri 40 61 64 87 --- 5 --- 0 --- 2 --- 0 --- 0 --- 1
Cissus nymphaeifolia 17 33 58 73 8 24 --- 0 --- 0 --- 0 --- 0 --- 0
Steganotaenia araliacea var. araliacea 20 28 58 60 --- 0 --- 0 --- 0 --- 1 --- 0 --- 1
Ficus cordata --- 0 49 27 --- 0 --- 0 --- 0 --- 0 --- 0 --- 0
Crassocephalum coeruleum --- 0 47 27 --- 0 --- 0 --- 0 --- 0 --- 1 --- 1
Actiniopteris radiata 8 17 45 47 11 19 --- 0 --- 0 --- 0 --- 0 --- 0
Berchemia discolor --- 0 44 47 --- 5 --- 9 --- 10 --- 3 2 13 --- 0
Triraphis ramosissima --- 0 42 27 --- 0 --- 0 --- 6 --- 0 --- 0 --- 1
Momordica humilis --- 0 41 20 --- 0 --- 0 --- 0 --- 1 --- 0 --- 0
Boscia albitrunca --- 11 40 47 --- 0 --- 0 --- 4 --- 6 --- 13 --- 15
Fingerhuthia africana --- 0 --- 0 64 71 --- 0 --- 10 --- 4 --- 0 11 23
Searsia marlothii --- 11 16 47 53 90 --- 12 --- 0 --- 19 --- 13 2 31
Dombeya rotundifolia 35 72 13 47 50 90 --- 0 --- 8 --- 3 --- 0 --- 22
Anthephora pubescens --- 22 --- 20 49 71 --- 9 --- 12 --- 12 --- 4 --- 9
Eragrostis nindensis --- 44 --- 33 45 100 4 47 12 57 --- 15 --- 3 --- 34
Heteropogon contortus 14 56 --- 20 45 95 --- 12 --- 39 --- 40 --- 13 --- 31
Ophioglossum polyphyllum --- 0 --- 0 43 29 --- 0 --- 2 --- 1 --- 0 --- 5
Anthephora schinzii --- 0 --- 0 --- 0 66 76 19 33 --- 0 --- 6 --- 2
Ipomoea adenioides --- 0 --- 0 --- 0 64 47 --- 0 --- 3 --- 0 --- 0
Tragus pedunculatus --- 0 --- 0 --- 0 59 38 --- 0 --- 0 --- 0 --- 0
Vahlia capensis --- 0 --- 0 --- 0 46 26 --- 0 --- 3 --- 0 --- 0
Pavetta zeyheri --- 6 --- 0 --- 24 44 62 --- 4 --- 18 --- 13 --- 14
Combretum hereroense --- 0 --- 0 --- 0 40 65 --- 16 17 40 --- 34 --- 15
Colophospermum mopane --- 0 --- 0 --- 0 --- 0 63 55 --- 1 --- 1 --- 11
Setaria pumila --- 33 --- 20 --- 14 --- 0 44 78 --- 9 --- 14 13 42
Aristida congesta subsp. congesta --- 0 --- 0 --- 0 --- 0 --- 0 58 40 --- 1 --- 1
Waltheria indica --- 6 --- 0 --- 0 --- 0 --- 0 50 42 --- 7 --- 5
Hyphaene petersiana --- 0 --- 0 --- 0 --- 0 --- 0 50 47 17 23 --- 4
Stipagrostis uniplumis var. uniplumis --- 6 --- 0 --- 0 --- 3 --- 10 49 63 --- 18 --- 26
Schizachyrium exile --- 6 --- 0 --- 0 --- 0 --- 0 45 28 --- 0 --- 0
Kyphocarpa angustifolia --- 0 --- 0 --- 0 --- 0 --- 4 44 37 --- 7 --- 9
Schmidtia pappophoroides --- 6 --- 0 --- 5 --- 0 --- 2 43 36 --- 3 --- 4
Pogonarthria fleckii --- 11 --- 0 --- 0 --- 6 23 43 43 63 --- 11 --- 16
Eragrostis rigidior --- 0 --- 0 --- 0 --- 0 --- 0 41 29 --- 3 --- 9
Spirostachys africana --- 11 --- 20 --- 14 --- 3 --- 43 26 67 43 89 --- 30
Kirkia acuminata 50 94 54 100 4 38 --- 0 --- 12 --- 1 --- 10 --- 7
Commiphora glaucescens 47 89 29 67 48 90 --- 0 --- 0 --- 0 --- 3 --- 2
Terminalia prunioides --- 17 --- 73 --- 76 --- 88 18 98 14 94 --- 90 --- 90
Dichrostachys cinerea --- 78 --- 67 --- 71 --- 35 --- 90 --- 91 16 96 16 95
Combretum apiculatum 17 100 --- 87 12 95 --- 74 --- 88 10 94 --- 52 --- 78
Grewia bicolor --- 44 --- 67 --- 48 --- 62 --- 69 13 83 18 90 --- 78
Senegalia mellifera subsp. detinens --- 11 --- 27 --- 67 --- 76 --- 47 20 86 --- 79 21 87
Commiphora glandulosa --- 28 --- 67 --- 62 13 79 18 86 --- 72 --- 45 --- 59
Melinis repens subsp. grandiflora 14 83 --- 73 --- 52 13 82 13 82 --- 60 --- 41 --- 53
Croton gratissimus 26 100 15 87 26 100 6 76 --- 39 --- 32 --- 52 --- 63
Urochloa brachyura --- 28 --- 20 --- 10 --- 21 20 71 28 82 23 75 --- 53
Grewia flavescens --- 44 --- 67 --- 19 --- 29 13 63 --- 40 --- 48 9 58
Vachellia nilotica --- 22 --- 20 --- 48 --- 6 --- 29 18 60 17 59 15 56
Combretum imberbe --- 6 --- 40 --- 52 15 62 --- 45 10 55 --- 45 --- 36
Vachellia reficiens / luederitzii --- 0 --- 0 --- 48 --- 21 --- 16 --- 38 21 56 27 63
Brachiaria deflexa --- 17 27 67 --- 19 --- 3 --- 29 --- 24 21 59 13 50
Aristida rhiniochloa --- 0 --- 0 --- 0 --- 44 22 53 37 71 --- 14 --- 33
Tragus racemosus --- 0 --- 13 --- 24 --- 44 15 47 --- 32 --- 32 --- 36
Aristida adscensionis --- 33 --- 13 --- 5 23 59 12 45 12 45 --- 24 --- 21
Enneapogon cenchroides --- 6 --- 27 --- 10 --- 44 --- 31 --- 21 16 46 --- 38
Sporobolus panicoides --- 22 --- 20 --- 5 --- 6 24 53 --- 36 --- 15 19 47
Bidens biternata 28 72 28 73 --- 29 --- 0 11 51 --- 9 --- 25 --- 37
Grewia villosa --- 22 --- 27 --- 14 --- 12 --- 22 --- 10 29 59 10 37
Mundulea sericea 13 56 --- 27 25 71 38 88 --- 18 --- 21 --- 14 --- 18
Lantana angolensis --- 6 --- 7 23 48 --- 3 --- 12 16 40 --- 11 26 50
Enneapogon scoparius --- 11 --- 33 26 57 --- 12 --- 24 --- 15 --- 18 15 45
Aristida effusa --- 6 --- 33 --- 14 --- 18 --- 29 --- 29 --- 17 10 34
Melhania acuminata --- 11 --- 7 --- 5 --- 3 --- 18 32 50 --- 23 --- 24
Seddera suffruticosa --- 0 --- 7 --- 19 --- 6 --- 22 18 36 --- 13 21 39
Eragrostis porosa --- 6 --- 40 --- 5 20 47 21 49 --- 4 --- 21 --- 27
Abutilon austro-africanum --- 17 --- 7 --- 14 --- 3 --- 20 --- 8 32 52 11 31
Grewia flava --- 6 --- 0 --- 14 --- 12 --- 12 19 35 --- 7 29 45
Commelina benghalensis --- 39 24 53 --- 5 --- 0 15 43 --- 9 --- 25 --- 29
Euclea undulata --- 22 --- 13 38 67 --- 6 --- 2 --- 18 11 37 --- 26
Tephrosia dregeana var. dregeana --- 11 --- 33 --- 19 --- 32 --- 27 --- 24 --- 24 --- 17
Cenchrus ciliaris --- 22 --- 20 --- 38 --- 0 --- 27 --- 4 --- 17 21 44
Indigofera charlieriana --- 0 --- 20 --- 19 --- 9 35 57 --- 14 --- 15 --- 27
Melhania virescens --- 6 --- 7 35 57 --- 6 --- 24 --- 3 --- 17 22 44
Pavonia burchellii --- 11 --- 33 --- 38 --- 3 --- 12 --- 12 --- 24 14 37
Achyranthes aspera var. sicula 21 50 29 60 --- 10 --- 3 --- 20 --- 6 10 38 --- 20
Evolvulus alsinoides --- 6 --- 7 --- 0 --- 3 --- 20 35 49 --- 17 --- 20
Eragrostis trichophora --- 0 --- 7 --- 0 --- 29 --- 6 24 38 --- 18 --- 27
Gymnosporia senegalensis --- 6 --- 20 --- 38 --- 26 --- 8 --- 22 9 31 --- 18
Peltophorum africanum 28 50 --- 20 --- 10 --- 3 --- 4 19 41 --- 17 --- 20
Ocimum americanum var. americanum --- 0 --- 0 --- 5 28 44 --- 8 28 44 --- 15 --- 15
Ziziphus mucronata --- 33 --- 13 25 48 --- 0 --- 2 --- 26 --- 23 --- 24
Otoptera burchellii --- 0 --- 7 --- 24 --- 6 --- 27 --- 23 --- 8 19 35
Phyllanthus pentandrus 15 44 28 60 --- 33 --- 15 --- 20 --- 3 --- 17 --- 24
Albizia anthelmintica --- 6 --- 7 --- 0 --- 3 --- 8 19 31 --- 27 16 28
Ipomoea sinensis --- 0 --- 7 --- 5 --- 0 38 51 --- 12 --- 20 13 28
Ocimum filamentosum --- 28 --- 13 --- 14 --- 0 14 33 --- 8 --- 21 11 30
Acalypha segetalis --- 28 31 60 --- 29 --- 6 7 33 --- 10 --- 24 --- 11
Kohautia aspera --- 0 --- 7 --- 5 --- 12 36 49 --- 9 --- 11 15 30
Ximenia americana 36 61 --- 7 --- 29 --- 9 --- 4 --- 18 10 32 --- 13
Monechma spartioides --- 0 --- 0 --- 10 --- 0 --- 6 20 29 --- 23 20 30
Enneapogon desvauxii --- 0 --- 0 --- 14 --- 15 20 33 --- 12 --- 8 21 34
Sporobolus fimbriatus --- 11 --- 7 --- 10 --- 0 --- 6 39 50 --- 23 --- 7
Limeum sulcatum --- 6 --- 27 --- 0 --- 12 15 31 --- 15 --- 18 --- 18
Microchloa caffra --- 17 --- 20 --- 14 21 41 12 33 --- 15 --- 6 --- 11
Flueggea virosa --- 11 29 53 15 38 --- 9 --- 24 --- 4 --- 17 --- 18
Rhynchosia minima --- 22 --- 20 16 33 --- 0 --- 12 --- 6 --- 18 10 28
Gisekia africana --- 11 --- 7 --- 0 23 38 --- 24 --- 10 --- 24 --- 11
Tragus berteronianus --- 0 --- 13 --- 0 --- 3 16 27 --- 17 --- 17 13 23
Acrotome inflata --- 11 --- 0 --- 5 --- 3 18 29 --- 15 --- 20 --- 19
Pupalia lappacea --- 11 21 40 --- 29 --- 12 --- 2 --- 14 9 28 --- 13
Helinus integrifolius --- 0 27 40 --- 10 --- 3 --- 12 --- 5 --- 13 22 36
Eragrostis echinochloidea --- 0 --- 0 --- 29 38 53 --- 10 --- 9 --- 8 --- 21
Dicoma tomentosa --- 0 --- 0 --- 0 --- 3 28 35 29 36 --- 8 --- 9
Rhynchosia totta --- 22 --- 20 --- 14 --- 3 --- 20 --- 18 --- 13 --- 16
Commiphora tenuipetiolata --- 22 --- 20 --- 5 32 50 --- 12 --- 13 --- 8 --- 13
Setaria verticillata --- 0 --- 27 --- 0 --- 0 --- 0 --- 14 27 35 --- 20
Clerodendrum ternatum --- 0 --- 13 --- 14 --- 3 --- 14 12 23 --- 8 13 23
Panicum maximum 29 44 --- 20 --- 5 --- 3 --- 0 --- 17 15 31 --- 11
Eragrostis lehmanniana 28 44 --- 13 --- 14 --- 3 --- 18 --- 13 --- 15 --- 14
Sericorema sericea --- 0 --- 0 --- 5 18 29 27 37 --- 8 --- 10 --- 16
Hibiscus caesius --- 0 --- 13 --- 29 --- 0 --- 4 --- 9 --- 15 19 29
Croton menyharthii --- 0 --- 7 --- 0 --- 6 --- 12 --- 18 31 37 --- 7
Sclerocarya birrea subsp. caffra 26 50 35 60 --- 10 --- 12 --- 18 --- 10 --- 10 --- 6
Aristida stipoides --- 6 --- 13 --- 10 40 53 --- 4 --- 18 --- 7 --- 10
Blepharis obmitrata --- 6 --- 20 --- 19 --- 0 --- 10 --- 5 --- 17 13 24
Erucastrum arabicum --- 6 --- 27 --- 10 --- 0 --- 18 --- 0 11 23 10 21
Hibiscus calyphyllus --- 6 25 33 --- 5 --- 0 --- 4 --- 1 --- 14 25 34
Asparagus nelsii --- 11 --- 20 32 48 --- 0 --- 18 --- 13 --- 7 --- 14
Commiphora africana --- 0 24 40 22 38 --- 6 --- 14 --- 6 --- 13 --- 16
Andropogon chinensis 37 61 --- 0 33 57 --- 18 --- 18 --- 6 --- 1 --- 7
Brachiaria malacodes --- 6 20 33 --- 24 --- 6 --- 12 --- 4 --- 11 6 20
Digitaria velutina --- 0 26 33 --- 0 --- 0 --- 8 --- 4 20 28 --- 18
Enteropogon macrostachyus --- 17 --- 13 --- 10 --- 0 --- 10 --- 8 12 23 --- 15
Grewia olukondae 26 33 --- 7 --- 0 --- 3 --- 0 24 32 --- 14 --- 4
Asparagus exuvialis --- 0 --- 27 --- 10 --- 6 --- 2 14 23 --- 14 --- 9
Pentarrhinum insipidum 29 44 --- 7 28 43 --- 0 --- 8 --- 1 --- 10 --- 14
Setaria sagittifolia --- 0 26 33 --- 5 --- 0 --- 2 --- 8 34 39 --- 3
Bothriochloa radicans --- 0 --- 0 --- 0 --- 3 24 24 --- 4 --- 10 18 20
Hermannia modesta --- 0 --- 7 --- 14 21 29 13 22 --- 1 --- 3 --- 14
Chloris virgata --- 0 --- 0 --- 0 --- 3 --- 16 --- 9 --- 10 18 19
Phyllanthus maderaspatensis --- 11 --- 7 --- 0 --- 15 --- 4 --- 15 --- 11 --- 11
Gymnema sylvestre --- 17 --- 20 --- 10 --- 3 --- 12 --- 12 --- 13 --- 7
Ximenia caffra 14 28 --- 27 20 33 --- 0 --- 2 --- 8 --- 8 --- 11
Spermacoce senensis --- 17 23 33 --- 5 --- 0 13 24 --- 10 --- 6 --- 7
Euphorbia inaequilatera --- 0 --- 0 --- 5 --- 0 39 37 --- 4 --- 10 --- 11
Aptosimum decumbens --- 0 --- 0 --- 0 --- 3 --- 14 15 17 --- 1 18 18
Megalochlamys marlothii --- 0 --- 0 --- 0 --- 0 --- 18 --- 1 --- 11 24 22
Solanum delagoense --- 11 --- 7 --- 14 --- 0 --- 12 --- 5 --- 3 16 21

Overview of the Terminalietea prunioidis:

5.1 Commiphoro glaucescentis-Kirkietalia acuminatae

5.1.1 Commiphoro glaucescentis-Kirkion acuminatae

5.1.1.1 Lanneo discoloris-Kirkietum acuminatae

5.1.1.2 Commiphoro glaucescentis-Kirkietum acuminatae

5.1.1.3 Commiphoro glaucescentis-Combretetum apiculati

5.2 Terminalietalia prunioidis

5.2.1 Unnamed group

5.2.1.1 Trago pedunculati-Ipomoeetum adenioidis

5.2.1.2 Combreto apiculati-Colophospermetum mopane

5.2.2 Terminalio prunioidis-Hyphaenion petersianae

5.2.2.1 Terminalio prunioidis-Hyphaenetum petersianae

5.2.3 Dichrostachyo cinereae-Terminalion prunioidis

5.2.3.1 Terminalio prunioidis-Spirostachyetum africanae

5.2.3.2 Dichrostachyo cinereae-Terminalietum prunioidis

5.1 Commiphoro glaucescentis - Kirkietalia acuminatae ord. nov.

Number of relevés: 54

Holotypus: Commiphoro glaucescentis-Kirkion acuminatae B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 228

Diagnostic species: Commiphora glaucescens, Kirkia acuminata, Dombeya rotundifolia, Danthoniopsis dinteri

Constant species: Combretum apiculatum

The Commiphoro glaucescentis-Kirkietalia acuminatae represent the mountain vegetation of the Karstveld. Various forms are known from as far afield as the Opuwo district in north-western Namibia (Viljoen 1980) as well as the Etosha National Park (Le Roux 1980), confirming that the Karstveld extends further west than covered in this paper. Within this study, three associations to Commiphoro glaucescentis-Kirkion acuminatae are described, with the Commiphoro glaucescentis-Kirkietum acuminatae designated as the type to the Commiphoro glaucescentis-Kirkion acuminatae, which in turn is the type to the order. There is no distinct altitudinal or aspect differentiation between these associations, rather the rock type, steepness and massiveness of the substrate seems to be deterministic.

5.1.1 Commiphoro glaucescentis - Kirkion acuminatae all. nov.

Number of relevés: 54

Type: Commiphoro glaucescentis-Kirkietum acuminatae B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 228

Diagnostic species: Commiphora glaucescens, Kirkia acuminata, Dombeya rotundifolia, Danthoniopsis dinteri

Constant species: Combretum apiculatum

5.1.1.1 Lanneo discoloris - Kirkietum acuminatae ass. nov.

Number of relevés: 18

Number of species observed: 149

Estimated number of species: 259

Average species density in 1000 m2: 41

Type relevé: 7943 (holotypus), sampled on 15 February 2008 at 19.45389°S, 17.66972°E (Mosbach)

Kirkia acuminata (t2) 10%, Lannea discolor (t2) 10%, Spirostachys africana (t2) 5%, Sclerocarya birrea subsp. caffra (t2) 0.5%, Combretum apiculatum subsp. leutweinii (t3) 5%, Dichrostachys cinerea (t3) 5%, Peltophorum africanum (t3) 5%, Spirostachys africana (t3) 5%, Commiphora glandulosa (t3) 1%, Commiphora tenuipetiolata (t3) 0.5%, Croton gratissimus var. subgratissimus (s1) 10%, Flueggea virosa (s1) 5%, Grewia flavescens (s1) 5%, Dombeya rotundifolia (s1) 2%, Mundulea sericea (s1) 1%, Ximenia americana (s1) 1%, Cissus nymphaeifolia (s1) 0.5%, Commiphora glaucescens (s1) 0.5%, Euphorbia guerichiana (s1) 0.5%, Ozoroa insignis (s1) 0.5%, Terminalia sericea (s1) 0.5%, Vachellia nilotica (s1) 0.5%, Vangueria infausta (s1) 0.5%, Ximenia caffra (s1) 0.5%, Cyphostemma congestum (s2) 0.5%, Grewia villosa (s2) 0.5%, Securidaca longepedunculata (s2) 0.5%, Panicum maximum (gp) 20%, Digitaria seriata (gp) 5%, Heteropogon contortus (gp) 1%, Cenchrus ciliaris (gp) 0.5%, Enneapogon scoparius (gp) 0.5%, Enteropogon macrostachyus (gp) 0.5%, Eragrostis lehmanniana (gp) 0.5%, Eustachys paspaloides (gp) 0.5%, Danthoniopsis dinteri (ga) 10%, Brachiaria deflexa (ga) 0.5%, Enneapogon cenchroides (ga) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Tephrosia purpurea (ga) 0.5%, Cheilanthes marlothii (hl) 2%, Hypoestes forskaolii (hl) 2%, Bidens biternata (hl) 1%, Cheilanthes dinteri (hl) 1%, Cleome monophylla (hl) 1%, Pellaea calomelanos (hl) 1%, Abutilon angulatum (hl) 0.5%, Acalypha segetalis (hl) 0.5%, Cardiospermum corindum (hl) 0.5%, Cheilanthes involuta (hl) 0.5%, Commelina benghalensis (hl) 0.5%, Erucastrum arabicum (hl) 0.5%, Hibiscus calyphyllus (hl) 0.5%, Hibiscus castroi (hl) 0.5%, Kyllinga alba (hl) 0.5%, Momordica balsamina (hl) 0.5%, Ocimum filamentosum (hl) 0.5%, Oxalis purpurascens (hl) 0.5%, Pavonia burchellii (hl) 0.5%, Pentarrhinum insipidum (hl) 0.5%, Phyllanthus pentandrus (hl) 0.5%, Pupalia lappacea (hl) 0.5%, Rhynchosia venulosa (hl) 0.5%, Solanum lichtensteinii (hl) 0.5%, Talinum caffrum (hl) 0.5%, Tragia okanyua (hl) 0.5%

Diagnostic species: Vangueria infausta, Pellaea calomelanos, Cheilanthes dinteri, Lannea discolor, Cleome monophylla, Kirkia acuminata, Macrotyloma axillare, Commiphora glaucescens, Ozoroa insignis, Andropogon gayanus var. polycladus, Merremia pinnata, Thunbergia aurea, Danthoniopsis dinteri, Ipomoea verbascoidea

Constant species: Croton gratissimus, Combretum apiculatum, Melinis repens subsp. grandiflora, Dichro­stachys cinerea, Dombeya rotundifolia, Bidens biternata, Ximenia americana, Andropogon chinensis

The Lanneo discoloris-Kirkietum acuminatae forms a tall, sub-continuous thicket dominated by the phanerophytes Kirkia acuminata, Croton gratissimus, Combretum apiculatum, Commiphora glaucescens and Lannea discolor. The grass sward consists of Danthoniopsis dinteri, Panicum maximum, Melinis repens subsp. grandiflora, Eragrostis porosa, Digitaria seriata and Aristida adscensionis (Figures 12a, 13a).

Figure 12. 

Typical structure of the associations of the Terminalietea prunioidis: (a) Lanneo discoloris-Kirkietum acuminatae; (b) Commiphoro glaucescentis-Kirkietum acuminatae; (c) Commiphoro glaucescentis-Combretetum apiculati; (d) Trago pedunculati-Ipomoeetum adenioidis; (e) Combreto apiculati-Colophospermetum mopane; (f) Terminalio prunioidis-Hyphaenetum petersianae; (g) Terminalio prunioidis-Spirostachyetum africanae; (h) Dichrostachyo cinereae-Terminalietum prunioidis.

Figure 13. 

Typical views of the associations of the Terminalietea prunioidis: (a) Lanneo discoloris-Kirkietum acuminatae, relevé 7951; (b) Commiphoro glaucescentis-Kirkietum acuminatae, relevé 7934; (c) Commiphoro glaucescentis-Combretetum apiculati, relevé 7971; (d) Trago pedunculati-Ipomoeetum adenioidis, relevé 2794; (e) Trago pedunculati-Ipomoeetum adenioidis during the peak rainy season; (f) Combreto apiculati-Colophospermetum mopane, relevé 8071; (g) Terminalio prunioidis-Hyphaenetum petersianae, relevé 2793; (h) Terminalio prunioidis-Spirostachyetum africanae, relevé 7771; (i) Dichrostachyo cinereae-Terminalietum prunioidis, relevé 8113.

The association occurs on moderately steep to steep mountain slopes, mostly of the Nosib Group and Abenab Subgroup type rocks (i.e. quarzites, dolomites, limestone, conglomerate). Large stones (20–60 cm) cover between 15 and 40% of the soil surface, whilst rocks (i.e. bigger than 60 cm) cover between 40 and 80%, sometimes even more. The soils are shallow (<30 cm deep) and medium-textured (Coetzee et al. 1998). The Lanneo discoloris-Kirkietum acuminatae occurs at altitudes of between 1290 and 1830 m a.s.l.

5.1.1.2 Commiphoro glaucescentis - Kirkietum acuminatae ass. nov.

Number of relevés: 15

Number of species observed: 156

Estimated number of species: 285

Average species density in 1000 m2: 44

Type relevé: 8018 (holotypus), sampled on 14 March 2008 at 19.46250°S, 16.90139°E (Olifantspoor)

Kirkia acuminata (t1) 20%, Sclerocarya birrea subsp. caffra (t1) 1%, Berchemia discolor (t2) 10%, Terminalia prunioides (t2) 10%, Commiphora mollis (t2) 1%, Commiphora glaucescens (t3) 10%, Commiphora mollis (t3) 10%, Combretum apiculatum subsp. apiculatum (s1) 10%, Senegalia erubescens (s1) 10%, Flueggea virosa (s1) 5%, Grewia bicolor (s1) 2%, Cissus nymphaeifolia (s1) 1%, Steganotaenia araliacea var. araliacea (s2) 0.5%, Triraphis ramosissima (gp) 1%, Danthoniopsis dinteri (ga) 5%, Brachiaria deflexa (ga) 2%, Melinis repens subsp. grandiflora (ga) 2%, Dactyloctenium aegyptium (ga) 1%, Eragrostis porosa (ga) 1%, Setaria sagittifolia (ga) 0.5%, Achyranthes aspera var. sicula (hl) 10%, Commelina benghalensis (hl) 10%, Bidens biternata (hl) 5%, Momordica humilis (hl) 5%, Acalypha ciliata (hl) 1%, Abutilon angulatum (hl) 0.5%, Actiniopteris radiata (hl) 0.5%, Cleome angustifolia subsp. diandra (hl) 0.5%, Corchorus tridens (hl) 0.5%, Crassocephalum coeruleum (hl) 0.5%, Gisekia africana (hl) 0.5%, Hibiscus elliottiae (hl) 0.5%, Ipomoea dichroa (hl) 0.5%, Neorautanenia mitis (hl) 0.5%, Phyllanthus pentandrus (hl) 0.5%, Rhynchosia totta (hl) 0.5%, Schkuhria pinnata (hl) 0.5%, Spermacoce senensis (hl) 0.5%, Thunbergia aurea (hl) 0.5%

Diagnostic species: Danthoniopsis dinteri, Cissus nymphaeifolia, Steganotaenia araliacea var. araliacea, Kirkia acuminata, Ficus cordata, Crassocephalum coeruleum, Actiniopteris radiata, Berchemia discolor, Triraphis ramosissima, Momordica humilis

Constant species: Croton gratissimus, Combretum apiculatum, Terminalia prunioides, Melinis repens subsp. grandiflora, Bidens biternata, Grewia flavescens, Grewia bicolor, Dichrostachys cinerea, Commiphora glaucescens, Commiphora glandulosa, Brachiaria deflexa

The Commiphoro glaucescentis-Kirkietum acuminatae forms a tall, sub-continuous thicket, dominated by the phanerophytes Kirkia acuminata, Commiphora glaucescens, Gyrocarpus americanus subsp. africanus, Croton gratissimus and Commiphora mollis. The grass sward is less diverse, with Danthoniopsis dinteri and Brachiaria malacodes dominating. Plectranthus cylindraceus (a leaf-succulent suffrutex) is also common (Figures 12b, 13b).

This association occurs on steep to very steep mountain slopes, mostly of the Tsumeb Subgroup rocks (mostly dolomites). Stone and rock cover is equally high as with the Lanneo discoloris-Kirkietum acuminatae, however more medium-sized stones (5 – 20 cm) are present. The association occurs at altitudes between 1250 and 1640 m a.s.l.

5.1.1.3 Commiphoro glaucescentis - Combretetum apiculati ass. nov.

Number of relevés: 21

Number of species observed: 131

Estimated number of species: 225

Average species density in 1000 m2: 40

Type relevé: 7910 (holotypus), sampled on 12 February 2008 at 19.54833°S, 17.46556°E (Ma Foi)

Ficus burkei (t2) 1%, Commiphora glaucescens (t3) 10%, Combretum apiculatum subsp. apiculatum (s1) 10%, Dichrostachys cinerea (s1) 10%, Senegalia mellifera subsp. detinens (s1) 10%, Terminalia prunioides (s1) 10%, Croton gratissimus var. subgratissimus (s1) 5%, Dombeya rotundifolia (s1) 5%, Elephantorrhiza suffruticosa (s1) 5%, Grewia flava (s1) 1%, Commiphora africana (s1) 0.5%, Flueggea virosa (s1) 0.5%, Gymnosporia senegalensis (s1) 0.5%, Lantana angolensis (s1) 0.5%, Searsia marlothii (s1) 0.5%, Ziziphus mucronata (s1) 0.5%, Cissus nymphaeifolia (s1) 0.1%, Aerva leucura (s2) 0.5%, Mundulea sericea (s2) 0.5%, Ehretia rigida (s2) 0.1%, Grewia bicolor (s2) 0.1%, Eragrostis nindensis (gp) 5%, Eragrostis lehmanniana var. lehmanniana (gp) 2%, Andropogon chinensis (gp) 0.5%, Heteropogon contortus (gp) 0.5%, Oropetium capense (gp) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Actiniopteris radiata (hl) 2%, Cyperus cuspidatus (hl) 1%, Bidens biternata (hl) 0.5%, Cheilanthes marlothii (hl) 0.5%, Clerodendrum ternatum (hl) 0.5%, Dipcadi glaucum (hl) 0.5%, Hibiscus caesius (hl) 0.5%, Ophioglossum polyphyllum (hl) 0.5%, Pavonia burchellii (hl) 0.5%, Pentarrhinum insipidum (hl) 0.5%, Phyllanthus pentandrus (hl) 0.5%, Rhynchosia venulosa (hl) 0.5%, Scadoxus multiflorus (hl) 0.5%, Eriospermum flagelliforme (hl) 0.1%, Gloriosa superba (hl) 0.1%, Enneapogon scoparius (gp) 10%, Fingerhuthia africana (gp) 10%, Anthephora pubescens (gp) 5%

Diagnostic species: Fingerhuthia africana, Searsia marlothii, Commiphora glaucescens, Dombeya rotundifolia, Anthephora pubescens, Eragrostis nindensis, Heteropogon contortus, Ophioglossum polyphyllum

Constant species: Croton gratissimus, Combretum apiculatum, Terminalia prunioides, Mundulea sericea, Dichrostachys cinerea, Senegalia mellifera subsp. detinens, Euclea undulata, Commiphora glandulosa

The Commiphoro glaucescentis-Combretetum apiculati forms a short, moderately closed thicket dominated by the phanerophytes Terminalia prunioides, Croton gratissimus, Commiphora glaucescens, Spirostachys africana, Kirkia acuminata, Dombeya rotundifolia, Dichrostachys cinerea and Combretum apiculatum. Opuntia ficus-indica has been found to be a common invader in this association. The grass sward is best developed of the three mountain associations, being dominated by Eragrostis nindensis, Enneapogon scoparius, Heteropogon contortus, Eragrostis scopelophila and Enneapogon desvauxii (Figures 12c, 13c).

This association is occurring on low hills and ridges as well as on mountain peaks, at a wide range of altitudes, between 1440 and 2020 m a.s.l., and on both the Abenab and Tsumeb Subgroups. The habitat is however less steep, being rolling to moderately steep. The substrate is also more fragmented, with gravel (0.2–2 cm) and small stones (2–5 cm) and medium stones prominently occurring on the soil surface (2%, 5% and up to 15%, respectively). Large stones and rocks cover about 40% of the soil surface. The soils are equally shallow as with the other mountain habitats.

5.2 Terminalietalia prunioidis ord. nov.

Number of relevés: 329

Type: Dichrostachyo cinereae-Terminalion prunioidis B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 412

Diagnostic species: Aristida rhiniochloa, Urochloa brachyura, Combretum hereroense, Senegalia mellifera subsp. detinens, Terminalia prunioides

Constant species: Dichrostachys cinerea, Grewia bicolor, Combretum apiculatum, Commiphora glandulosa, Melinis repens subsp. grandiflora, Croton gratissimus, Spirostachys africana, Grewia flavescens, Vachellia nilotica, Combretum imberbe, Vachellia reficiens / luederitzii

The Terminalietalia prunioidis are subdivided into three groups, of which the latter two are recognised as alliances. The Dichrostachyo cinereae-Terminalion prunioidis is designated as the type for this order. The Terminalietalia prunioidis represent the Karstveld plains to the north of the Otavi Mountain Range. The first group is characterised by the occurrence of Anthephora schinzii together with Terminalia prunioides, Commiphora glandulosa, Combretum apiculatum and Melinis repens subsp. grandiflora. Two associations have been classified into this group. However, as the composition and habitats of these two groups vary widely, they cannot be grouped into an alliance.

5.2.1.1 Trago pedunculati - Ipomoeetum adenioidis ass. nov.

Number of relevés: 34

Number of species observed: 75

Estimated number of species: 176

Average species density in 1000 m2: 26

Type relevé: 2794 (holotypus), sampled on 3 April 2003 at 19.25611°S, 18.48389°E (Baden)

Terminalia prunioides (t3) 2%, Terminalia prunioides (s1) 10%, Combretum apiculatum subsp. apiculatum (s1) 2%, Senegalia mellifera subsp. detinens (s1) 2%, Combretum hereroense (s1) 1%, Croton gratissimus var. gratissimus (s1) 1%, Grewia bicolor (s1) 1%, Pavetta zeyheri (s1) 1%, Rhigozum brevispinosum (s1) 1%, Ipomoea adenioides (s2) 2%, Mundulea sericea (s2) 2%, Stipagrostis uniplumis var. uniplumis (gp) 2%, Eragrostis echinochloidea (gp) 1%, Oropetium capense (gp) 1%, Anthephora schinzii (ga) 5%, Aristida adscensionis (ga) 1%, Eragrostis porosa (ga) 1%, Melinis repens subsp. grandiflora (ga) 1%, Tragus pedunculatus (ga) 1%, Gisekia africana (hl) 1%, Hermannia modesta (hl) 1%, Phyllanthus maderaspatensis (hl) 1%, Tephrosia dregeana var. dregeana (hl) 1%

Diagnostic species: Anthephora schinzii, Ipomoea adenioides, Tragus pedunculatus, Vahlia capensis, Pavetta zeyheri

Constant species: Terminalia prunioides, Mundulea sericea, Melinis repens subsp. grandiflora, Commiphora glandulosa, Senegalia mellifera subsp. detinens, Croton gratissimus, Combretum apiculatum, Combretum hereroense, Grewia bicolor, Combretum imberbe

The Trago pedunculati-Ipomoeetum adenioidis forms a short, semi-open bushland dominated by Terminalia prunioides, Senegalia mellifera subsp. detinens and Combretum apiculatum. The grass sward is relatively sparse, being dominated by Melinis repens subsp. grandiflora, Anthephora schinzii, Tragus berteronianus, Panicum coloratum, Eragrostis pilgeriana and Eragrostis nindensis (Figures 12d, 13d).

The habitat of this association is formed by denuded plates of calcrete, often associated with slight depressions, or, e.g. along the B6 trunk road, associated with a slight rise in topography forming a natural dam causing water to accumulate. This results in temporary flooding and water logging during the peak rainy season (Figure 13e). Soils are found only in the crevices between the calcrete blocks (near to 80% stone and rock cover). The shallow water evaporates soon, leaving especially the herbaceous layer without an adequate water supply. Consequently, most of these are short-lived annuals. Notable exceptions are Panicum coloratum, which is known to prefer pans and watercourses (i.e. waterlogged soils) (Gibbs Russell et al. 1990), and Eragrostis nindensis, which is known to be a poikilohydric plant (Van der Willigen et al. 2003). The phanerophytes also appear stunted, barely reaching 2 m height. The altitude ranges between 1140 and 1300 m a.s.l.

5.2.1.2 Combreto apiculati - Colophospermetum mopane ass. nov.

Number of relevés: 49

Number of species observed: 190

Estimated number of species: 305

Average species density in 1000 m2: 41

Type relevé: 8022 (holotypus), sampled on 14 March 2008 at 19.50250°S, 16.93444°E (Derna)

Colophospermum mopane (t1) 5%, Spirostachys africana (t2) 1%, Colophospermum mopane (t3) 60%, Terminalia prunioides (t3) 20%, Combretum apiculatum subsp. apiculatum (s1) 5%, Grewia bicolor (s1) 5%, Senegalia cinerea (s1) 5%, Dichrostachys cinerea (s1) 2%, Croton gratissimus var. gratissimus (s1) 1%, Croton menyharthii (s1) 1%, Grewia avellana (s1) 1%, Megalochlamys marlothii (s2) 0.5%, Bothriochloa radicans (gp) 2%, Enteropogon macrostachyus (gp) 2%, Enneapogon scoparius (gp) 0.5%, Microchloa caffra (gp) 0.5%, Aristida rhiniochloa (ga) 2%, Eragrostis porosa (ga) 2%, Setaria pumila (ga) 2%, Aristida effusa (ga) 1%, Melinis repens subsp. grandiflora (ga) 1%, Sporobolus panicoides (ga) 1%, Brachiaria deflexa (ga) 0.5%, Abutilon austro-africanum (hl) 0.5%, Bidens biternata (hl) 0.5%, Hibiscus calyphyllus (hl) 0.5%, Hibiscus elliottiae (hl) 0.5%, Indigastrum parviflorum (hl) 0.5%, Ipomoea sinensis (hl) 0.5%, Ocimum filamentosum (hl) 0.5%, Ruellia prostrata (hl) 0.5%

Diagnostic species: Colophospermum mopane

Constant species: Terminalia prunioides, Dichro­stachys cinerea, Combretum apiculatum, Commiphora glandu­losa, Melinis repens subsp. grandiflora, Setaria pumila, Urochloa brachyura, Grewia bicolor, Grewia flavescens

The Combreto apiculati-Colophospermetum mopane forms a short, moderately closed bushland, domi­na­ted by the phanerophytes Terminalia prunioides, Colopho­spermum mopane, Dichrostachys cinerea, Combre­tum apiculatum and Commiphora glandulosa. The grass sward consists of Eragrostis nindensis, Setaria pumila, Eragrostis porosa, Enneapogon desvauxii, Urochloa brachyura, Ennea­pogon cenchroides and Anthephora schinzii. The annual herb Seri­corema sericea and sedges Cyperus hamulosus and Eleocharis atropurpurea are also conspicuous in this association (Figures 12e, 13f).

Le Roux (Le Roux 1980; Le Roux et al. 1988) describes a ‘Thai-tkab veld’ and a ‘Maroela Association’ along the eastern part of the Etosha National Park, bordering the present study area. These veld types are dominated by Terminalia prunioides, Colophospermum mopane, Combretum apiculatum and Spirostachys africana. Within the Maroela association, some Sclerocarya birrea trees are found. This is essentially the same as the Combreto apiculati-Colophospermetum mopane under discussion here. Le Roux describes the soils on rises as shallow leptosols on calcrete boulders, whilst in the depressions ‘Arcadia’ form soils (i.e. vertisols) are present (Soil Classification Working Group 1991). The topography is generally flat, at an altitudinal range of between 1140 and 1310 m a.s.l..

The occurrence of Colophospermum mopane is not restricted to the Combreto apiculati-Colophospermetum mopane. The species occurs intermittently within the Dichrostachyo cinereae-Terminalietum prunioidis to the west and north-west of Tsumeb, gradually increasing in abundance. Anecdotal evidence has it that the species occurred far more east of its present distribution area, but over-utilisation for construction timber and especially mine props in the Tsumeb Mine during the early previous Century led to the gradual retreat of the species to the west.

5.2.2 Terminalio prunioidis-Hyphaenion petersianae all. nov.

Synopsis:

Number of relevés: 78

Type: Terminalio prunioidis-Hyphaenetum petersianae B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 216

This alliance consists of a single association, which also serves as its type.

5.2.2.1 Terminalio prunioidis-Hyphaenetum peter­sia­nae ass. nov.

Number of relevés: 78

Number of species observed: 216

Estimated number of species: 376

Average species density in 1000 m2: 40

Type relevé: 2793 (holotypus), sampled on 3 April 2003 at 19.21833°S, 18.52417°E (Elandslaagte)

Hyphaene petersiana (t2) 1%, Spirostachys africana (t2) 1%, Commiphora glandulosa (t3) 1%, Terminalia prunioides (s1) 40%, Combretum apiculatum subsp. apiculatum (s1) 5%, Dichrostachys cinerea (s1) 5%, Peltophorum africanum (s1) 5%, Vachellia nilotica (s1) 5%, Grewia bicolor (s1) 2%, Hyphaene petersiana (s1) 2%, Senegalia mellifera subsp. detinens (s1) 2%, Albizia anthelmintica (s1) 1%, Grewia flava (s1) 1%, Ximenia caffra (s1) 1%, Ziziphus mucronata subsp. mucronata (s1) 1%, Aristida congesta (gp) 1%, Eragrostis trichophora (gp) 1%, Heteropogon contortus (gp) 1%, Sporobolus fimbriatus (gp) 1%, Stipagrostis uniplumis var. uniplumis (gp) 1%, Urochloa brachyura (ga) 5%, Aristida adscensionis (ga) 2%, Aristida effusa (ga) 2%, Brachiaria deflexa (ga) 2%, Aristida rhiniochloa (ga) 1%, Digitaria velutina (ga) 1%, Enneapogon cenchroides (ga) 1%, Melinis repens subsp. grandiflora (ga) 1%, Sporobolus panicoides (ga) 1%, Tragus racemosus (ga) 1%, Pogonarthria fleckii (ga) 0.1%, Monechma spartioides (hl) 5%, Evolvulus alsinoides (hl) 1%, Indigofera charlieriana (hl) 1%, Limeum fenestratum (hl) 1%, Melhania acuminata (hl) 1%, Ocimum americanum var. americanum (hl) 1%, Otoptera burchellii (hl) 1%, Phyllanthus maderaspatensis (hl) 1%, Pupalia lappacea (hl) 1%, Rhynchosia venulosa (hl) 1%, Seddera suffruticosa (hl) 1%, Talinum crispatulum (hl) 1%, Tephrosia dregeana var. dregeana (hl) 1%

Diagnostic species: Aristida congesta subsp. congesta, Hyphaene petersiana, Waltheria indica, Stipagrostis uniplumis var. uniplumis, Sporobolus fimbriatus, Schmidtia pappophoroides, Pogonarthria fleckii, Schizachyrium exile, Kyphocarpa angustifolia, Eragrostis rigidior, Aristida rhi­nio­chloa, Evolvulus alsinoides

Constant species: Terminalia prunioides, Combretum apiculatum, Dichrostachys cinerea, Senegalia mellifera subsp. detinens, Grewia bicolor, Urochloa brachyura, Commiphora glandulosa, Spirostachys africana, Vachellia nilotica

The Terminalio prunioidis-Hyphaenetum petersianae forms a tall, sub-continuous thicket dominated by the phanerophytes Terminalia prunioides, Combretum apiculatum, Spirostachys africana, Senegalia mellifera subsp. detinens, Dichrostachys cinerea, Vachellia reficiens / luederitzii, Vachellia nilotica, Hyphaene petersiana, Croton gratissimus and Commiphora glandulosa. The grass sward is dominated by Pogonarthria fleckii, Aristida congesta subsp. congesta, Schizachyrium exile, Aristida rhiniochloa, Urochloa brachyura, Eragrostis trichophora, Eragrostis rigidior, Cymbopogon caesius, Chrysopogon nigritanus and Aristida effusa. The leaf succulent Sansevieria pearsonii is also conspicuous in this association (Figures 12f, 13g).

The Terminalio prunioidis-Hyphaenetum petersianae forms a distinct zone between the eastern, north-eastern and southern plains and the adjacent riverine habitats (Omuramba Ovambo and Omuramba Omatako). This is locally referred to as the ‘Palmvlakte´ (‘palm plains’, referring to the presence of the makalani palm, Hyphaene petersiana). Hyphaene petersiana is known to occur in soils with a shallow water table, e.g. along the fringes of the Oshana system in central-northern Namibia (Fanshawe 1967; Mendelsohn et al. 2000, 2013). Also Chrysopogon nigritanus is known to occur in close proximity to wetlands (Gibbs Russell et al. 1990). The soils are generally without stone cover, flat and at an altitudinal range of between 1150 and 1240 m a.s.l.

5.2.3 Dichrostachyo cinereae-Terminalion prunioidis all. nov.

Number of relevés: 169

Type: Dichrostachyo cinereae-Terminalietum prunioidis B. Strohbach & M. Strohbach 2023 (see below)

Number of species observed: 316

Constant species: Dichrostachys cinerea, Terminalia prunioides, Senegalia mellifera subsp. detinens, Grewia bicolor, Combretum apiculatum, Urochloa brachyura, Vachellia reficiens / luederitzii, Croton gratissimus, Vachellia nilotica, Spirostachys africana, Grewia flavescens, Brachiaria deflexa, Commiphora glandulosa, Melinis repens subsp. grandiflora, Grewia villosa, Enneapogon cenchroides

No diagnostic species were identified.

This order, representing the Karstveld plains to the east, north and west of the Otavi mountain range, are characterised by the constant occurrence of Dichrostachys cinerea, Terminalia prunioides, Senegalia mellifera subsp. detinens, Grewia bicolor, Combretum apiculatum and Urochloa brachyura. Two associations were identified under this alliance.

5.2.3.1 Terminalio prunioidis-Spirostachyetum africana e le Roux ex B. Strohbach & M. Strohbach ass. nov.

Number of relevés: 71

Number of species observed: 185

Estimated number of species: 356

Average species density in 1000 m2: 35

Type relevé: 8062 (holotypus), sampled on 17 March 2008 at 18.90972°S, 17.23694°E (Onkoshi)

Spirostachys africana (t2) 10%, Terminalia prunioides (t2) 10%, Vachellia luederitzii (t3) 5%, Albizia anthelmintica (t3) 1%, Terminalia prunioides (t3) 1%, Dichrostachys cinerea (s1) 10%, Senegalia mellifera subsp. detinens (s1) 10%, Terminalia prunioides (s1) 10%, Croton gratissimus var. subgratissimus (s1) 5%, Vachellia nilotica (s1) 5%, Grewia bicolor (s1) 2%, Grewia villosa (s1) 2%, Croton menyharthii (s2) 10%, Eragrostis porosa (ga) 10%, Enneapogon cenchroides (ga) 2%, Brachiaria deflexa (ga) 1%, Setaria sagittifolia (ga) 1%, Setaria verticillata (ga) 1%, Urochloa brachyura (ga) 1%, Chloris pycnothrix (ga) 0.5%, Digitaria velutina (ga) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Tragus berteronianus (ga) 0.5%, Tragus racemosus (ga) 0.5%, Erucastrum arabicum (hl) 5%, Achyranthes aspera var. sicula (hl) 2%, Bidens biternata (hl) 2%, Acrotome inflata (hl) 1%, Limeum sulcatum (hl) 1%, Abutilon austro-africanum (hl) 0.5%, Acrachne racemosa (hl) 0.5%, Cucumis anguria (hl) 0.5%, Euphorbia inaequilatera (hl) 0.5%, Hibiscus calyphyllus (hl) 0.5%, Hibiscus elliottiae (hl) 0.5%, Hirpicium gazanioides (hl) 0.5%, Ipomoea sinensis (hl) 0.5%, Kyphocarpa angustifolia (hl) 0.5%, Melhania virescens (hl) 0.5%

Constant species: Dichrostachys cinerea, Terminalia prunioides, Grewia bicolor, Spirostachys africana, Sene­galia mellifera subsp. detinens, Urochloa brachyura, Brachiaria deflexa

Le Roux (1980) and Le Roux et al. (1988) described a Terminalia prunioides-Spirostachys africana woodland occurring at and south of Namutoni in the Etosha National Park. Here we validate the name according to the ICPN.

The same vegetation, dominated by Terminalia prunioides, Spirostachys africana, Dichrostachys cinerea, Urochloa brachyura, Eragrostis porosa, Senegalia mellifera subsp. detinens, Grewia bicolor, Croton gratissimus, Brachiaria de­flexa, Croton menyharthii, Vachellia nilotica, Kirkia acuminata, Hypoestes forskaolii, Grewia olukondae, Ficus burkei, Enneapogon desvauxii, Combretum imberbe and Combretum apiculatum occurs widespread as riparian forest in and around the Omuramba Ovambo. In the middle reaches, within the Parkiesveld landscape, the Terminalio prunioidis-Spirostachyetum africanae form distinct tree islands in the grassland matrix formed by the Aristido stipoidis-Willkommietum sarmentosae, often enclosing an ephemeral vley of the Nymphoides indica-Echinochloa pyramidalis community (Figures 6c, 7a). The availability of shallow ground water often results in the inclusion of Sclerocarya birrea and/or Adansonia digitata trees in these forest islands (e.g. at the ‘Giant Baobab Tree’ Monument on the farm Die Park.) The association forms a tall, sub-continuous thicket (Figures 12g, 13h). The soils are of fluvial origin, often sandy, and generally organically enriched from litter. No stone cover was observed. The topography is flat, at an altitudinal range of between 1150 and 1310 m a.s.l.

5.2.3.2 Dichrostachyo cinereae - Terminalietum prunioidis ass. nov.

Number of relevés: 98

Number of species observed: 291

Estimated number of species: 467

Average species density in 1000 m2: 44

Type relevé: 8104 (holotypus), sampled on 16 April 2008 at 19.15389°S, 17.62694°E (Pasadena)

Vachellia luederitzii (t2) 2%, Terminalia prunioides (t3) 10%, Combretum imberbe (t3) 1%, Commiphora glandulosa (t3) 1%, Commiphora tenuipetiolata (t3) 1%, Terminalia prunioides (s1) 60%, Dichrostachys cinerea (s1) 10%, Combretum apiculatum subsp. apiculatum (s1) 2%, Croton gratissimus var. subgratissimus (s1) 2%, Grewia bicolor (s1) 2%, Peltophorum africanum (s1) 2%, Flueggea virosa (s1) 1%, Montinia caryophyllacea (s1) 1%, Mundulea sericea (s1) 1%, Ozoroa insignis (s1) 1%, Vachellia nilotica (s1) 1%, Ziziphus mucronata (s1) 1%, Spirostachys africana (s1) 0.5%, Solanum tettense var. renschii (s2) 5%, Lantana angolensis (s2) 1%, Ehretia alba (s2) 0.5%, Megalochlamys marlothii (s2) 0.5%, Senegalia mellifera subsp. detinens (s2) 0.5%, Maerua juncea (s2) 0.1%, Cenchrus ciliaris (gp) 2%, Heteropogon contortus (gp) 1%, Enneapogon scoparius (gp) 0.5%, Enteropogon macrostachyus (gp) 0.5%, Eragrostis lehmanniana var. lehmanniana (gp) 0.5%, Eragrostis nindensis (gp) 0.5%, Setaria pumila (ga) 5%, Sporobolus panicoides (ga) 2%, Aristida adscensionis (ga) 1%, Eragrostis porosa (ga) 1%, Urochloa brachyura (ga) 1%, Aristida effusa (ga) 0.5%, Aristida rhiniochloa (ga) 0.5%, Brachiaria malacodes (ga) 0.5%, Enneapogon cenchroides (ga) 0.5%, Enneapogon desvauxii (ga) 0.5%, Melinis repens subsp. grandiflora (ga) 0.5%, Setaria verticillata (ga) 0.5%, Stipagrostis hirtigluma subsp. hirtigluma (ga) 0.5%, Tragus racemosus (ga) 0.5%, Rhynchosia minima (hl) 5%, Kohautia aspera (hl) 2%, Melhania virescens (hl) 2%, Sericorema sericea (hl) 2%, Abutilon austro-africanum (hl) 1%, Acrotome inflata (hl) 1%, Bidens biternata (hl) 1%, Blepharis leendertziae (hl) 1%, Erucastrum arabicum (hl) 1%, Calostephane divaricata (hl) 0.5%, Eriospermum flagelliforme (hl) 0.5%, Euphorbia inaequilatera (hl) 0.5%, Hermannia modesta (hl) 0.5%, Hibiscus caesius (hl) 0.5%, Hirpicium gazanioides (hl) 0.5%, Ipomoea sinensis (hl) 0.5%, Melhania acuminata (hl) 0.5%, Otoptera burchellii (hl) 0.5%, Polygala albida subsp. albida (hl) 0.5%, Seddera suffruticosa (hl) 0.5%, Solanum delagoense (hl) 0.5%, Tephrosia dregeana var. dregeana (hl) 0.5%

Diagnostic species: none

Constant species: Dichrostachys cinerea, Terminalia prunioides, Senegalia mellifera subsp. detinens, Grewia bicolor, Combretum apiculatum, Vachellia reficiens / lueder­itzii, Croton gratissimus

The Dichrostachyo cinereae-Terminalietum prunioidis forms a short, sub-continuous thicket dominated by the phanerophytes Terminalia prunioides, Dichro­stachys cinerea, Senegalia mellifera subsp. detinens, Vachellia reficiens / luederitzii and Croton gratissimus. The grass sward is not well developed and dominated by few perennial and mostly annual species: Enneapogon desvauxii, Urochloa brachyura, Eragrostis porosa, Setaria pumila, Heteropogon contortus, Enteropogon macro­stachyus, Pogonarthria fleckii and Aristida adscensionis (Figures 12h, 13i). Bush encroachment is a serious threat to this association.

Initial classification results indicated a potential subdivision into three subunits, however the composition differences suggest rather observer and seasonal bias. For this reason, the three subunits have been combined as one.

This association occurs widespread on the plains north, east and west of the Otavi mountain range, often also in the valleys between these mountains. Several relevés have been classified into this association south of the Otavi mountain range, in a mosaic with the Cenchro ciliaris-Senegalietum detinentis and the Eucleo undulatae-Oleetum africanae, emphasising the transitional nature of the northern Thornshrub savanna. The soils are typical mollic Leptosols or leptic Regosols on shallow calcrete. Stone cover varies between 5 and 15% cover, with a general mixture of small, medium and large stones. The landscapes are flat to gently undulating, ranging between 1140 and 1600 m a.s.l.

Biodiversity indices

According to the observed species richness (alpha diversity), the community types fall into three groups (Figure 14a): The wetland associations (1.1 and 1.2) and the habitat-wise closely related Sporobolus-Odyssea paucinervis association (2.1.1) have the lowest number of species. Of intermediate richness are the three grassland types (2.1.2, 2.2.1 and 2.2.2) as well as the Terminalio sericeae-Schinziophyetum rautanenii (4.1) and the Trago pedunculati-Ipomoeetum adenioidis (5.2.1). The lower species richness of the Aristido stipoidis-Willkommietum sarmentosae and Trago pedunculati-Ipomoeetum adenioidis is easily explained by the harsh habitat provided by the shallow soils combined with water logging during the rainy season. All other savanna types display a variable, but generally high species richness.

The gamma diversity indicated similar trends as the species richness (Figure 14b). In many cases the estimated number of species was significantly higher than the observed number. This can be an indicator for both a high internal variability within the associations and possibly also a general undersampling.

Figure 14. 

Biodiversity indicators for the various associations described above. (a) Species richness per relevé sampled on 1000 m2; (b) Gamma diversity for the various associations, indicating both observed and estimated number of species; (c) Simpson’s Index (D) indicating dominance; (d) Smith-Wilson Index (Evar) indicating evenness.

According to the Simpson’s Index, the three wetland types (including the Sporobolo-Odysseetum paucinervis) (1.1, 1.2 and 2.1.1) show a relatively lower degree of dominance (Figure 14c). All other associations are dominated by few species, whilst most species occur with relatively low cover. Of note is the high dominance associated with low variability of the Terminalio sericeae-Schinziophyetum rautanenii (4.1). This could be a result of a few large trees (either Schinziophyton rautanenii or Pterocarpus angolensis) dominating and overshading the stand, resulting also in a lower number of species observed in the association (Figure 14a). This trend is also confirmed by a greater evenness score of the Smith-Wilson Index for this association (Figure 14d).

Environmental drivers

The NMS produced an ordination in three dimensions, with the final stress for the best solution being 19.6%, and a final instability of 0.00000, after 118 iterations. The randomised data in the Monte Carlo test did not result in a stable solution after 249 iterations. The ordination graph is presented in Figure 15. The tree main vegetation types, Thornbush – Karst transition, Kalahari and the Terminali­etea prunioidis are moderately well separated. Especially the Terminalietea prunioidis and the Thornbush – Karst transition vegetation are indistinguishable on Axis 3. The main environmental drivers, as determined by biplots, were soil depth (r = -0.457) for Axis 1, sandiness (r = -0.332), slope (r = 0.338), rock cover (r = 0.356) and mean annual precipitation (r = 0.348) for Axis 2, as well as gravel cover (r = -0.508) and small stone cover (r = -0.331) for Axis 3. The relatively low correlations necessitated reducing the joint plot cutoff level to r2 = 0.100 as compared to the default value for r2 = 0.200.

From the ordination diagrams it is clear that the Kalahari types favour deep soils, the Thornbush – Karstveld transition types the more sandy soils towards the southern study area, whilst the Terminalietea prunioidis associations are concentrated on mollic soils and/or stony to rocky soils. This is confirmed by the species distribution of some of the characteris phanerophytic species (Figure 16): Typically, Terminalia sericea, Combretum collinum and Vachellia erioloba favour deep, sandy soils, whilst Senegalia mellifera subsp. detinens and Olea europea subsp. africana prefer the more sandy, not necessarily deep soils south of the Karstveld. Spirostachys africana and Terminalia prunioides prefer shallow loamy to clayey (mollic) soils, whilst Kirkia acuminata and Commiphora glaucescens clearly prefer steep, rocky habitats, however often associated with deepish (> 50 cm) soil pockets amongst the rocks. As major encroaching species, Dichro­stachys cinerea shows no particular preference for any habitat. As the environmental variables used in this modelling are qualitative rather than empirically measured, these trends are also to be seen as indicative rather than predictive.

To illustrate the distribution of associations within the landscape, classified relevés within two 30 km wide transects (see Figure 2) were selected and graphed against the position and topography. These graphic representation of the distribution of vegetation associations are presented in Figure 17. The high degree of mosaicking especially within the Otavi mountain range and along the Omuramba Ovambo is clearly illustrated.

Figure 15. 

NMS ordination diagrams for the three savanna vegetation types, being the Thornbush – Karst transition, the Kalahari and the Terminalietea prunioidis. Top: Axis 1 against Axis 2; bottom Axis 1 against Axis 3.

Figure 16. 

Selected species’ response to the main environmental drivers in the Karstveld.

Figure 17. 

Schematic representation of the main vegetation associations across the topographic gradients represented by the transects in Figure 2. The altitude (y-axis) has been exaggerated for visualisation purposes, i.e. is not to scale. (a) Transect 1 from SW to NE. (b) Detail of the last 30 km of transect 1 (NE point), to show details regarding the mosaicking of vegetation associations around the Omuramba Ovambo. (c) Transect 2 from SE to NW. Note the Hoab Valley (ca 60 km from the start of the transect) is completely cleared and tilled for crop production, thus no associations are indicated there.

Conclusions

With this paper, we formally describe 17 new associations with two new subassociations within a major landscape, the Karstveld sensu Giess (1998) in north-central Namibia. Large parts of this landscape belong to the newly described Terminaletea prunioidis. All associations are clearly defined by way of diagnostic species (see Tables 25), yet there is a high variability in the composition of the associations. This is evident especially within the Terminalio prunioidis-Hyphaenetum petersianae, Terminalio prunioidis-Spiro­stachyetum africanae and Dichrostachyo cinereae-Termina­lietum prunioidis. Elements of the Combreto apiculati-Colophospermetum mopane have been found with the Dichrostachyo cinereae-Terminalietum prunioidis; whilst elements of the Dichrostachyo cinereae-Terminali­etum prunioidis have been found within the Cenchro cili­aris-Senegalietum detinentis. These mosaicking trends are also clearly illustrated by the NMS results (Figure 15).

With continued review of available data and unpublished reports (e.g. Le Roux 1980; Viljoen 1980; Becker 2001; Marufu 2023), further associations and communities belonging to the also newly described Commpihoro glaucentis-Kirkietalia acuminata will be identified and described in especialy the Kunene Region of north-western Namibia, as here an generaly overlooked, but important extension of the Otavi Group carbonate rocks is situated (South African Committee for Stratigraphy 1980; Miller 1997; Giess 1998). There are also indications that the vegetation of the Aha Hills in far-eastern Otjozondjupa Region, Namibia, and possibly the Tsodilo Hills, north-western Botswana, could be part of this order (Hines 1992; Wendorff 2005). Likewise, the newly described Terminalietalia prunioidis has outliers in the northern Oshikoto region, beyond the present study area, the Naye-Naye area of easter Otjozondjupa region as well as between Ghanzi and Maun in north-western Botswana (Cole and Brown 1976; Hines 1992; Strohbach 2000, 2014). In how far this order overlaps or can be separated from the Mopane Savanna sensu Giess (1998) to the west (as Terminalia prunioides is in vast parts co-dominant with Colophospermum mopane), will only be revealed by further reviews (Le Roux 1980; Viljoen 1980; Le Roux et al. 1988; Giess 1998; Becker 2001; Du Plessis 2001; Siebert et al. 2003; Marufu 2023).

The higher syntaxonomic divisions of the described associations of the Kalahari, Thornbush – Karstveld transistion and wetlands and grasslands remains even more speculative. For the Kalahari vegetation, a good start has been made with the description of the vegetation in the eastern Otjozondjupa and Omaheke Regions (Strohbach 2014), however, this landscape extends throughout large parts of central Botswana into north-westen South Africa as part of the Kalahari Acacia-Baikiaea woodlands ecoregion (Olson et al. 2001; Spriggs 2001b). Also, the differentiation from this ecoregion to the Zambezian Baikiaea woodlands ecoregion (Olson et al. 2001; Vetter 2001) is yet to be determined, as this forms a very gradual transition according to increasing rainfall into central Angola (Revermann et al. 2016). It is likely that the Terminalio sericeae-Schinziophyetum rautanenii forms part of the Zambezian Baikiaea woodlands ecoregion because of the presence of Pterocarpus angolensis and Schinziphyton rautanenii, whilst the three other associations form part of the Kalahari Acacia-Baikiaea woodlands ecoregion.

The vegetation of the Namibian Thornbush savannah is presently under review, and will include the higher syntaxonomic placement of the four associations described as part of the Thornbush – Karstveld transition. A basis for this revision is the earlier work by M. Strohbach (2002), but will also include further data and more recent publications covering parts of the Namibian Savanna Woodlands ecoregion (Olson et al. 2001; Spriggs 2001c; Strohbach 2014, 2019, 2021).

The higher syntaxonomic placement of the grass- and wetland types stays problematic. The Sporobolus dominated (ishana type) grasslands have been best studied to date, with accounts available from the Etosha Pan halophytic ecoregion, the Cuvelai Basin, the Naye-Naye panveld and also from the Zambezi Region in north-eastern Namibia (Le Roux et al. 1988; Schlettwein 1991; Hines 1992; Clarke 1999; Strohbach 2000; Olson et al. 2001; Spriggs 2001a, Lushetile 2009; Kangombe 2010). Although a general description of wetland types exists for north-eastern Namibia, this does not include detailed floristic descriptions (Hines 1993). Additionally, compounded by limited data, the three wetland communities found within this study could not be formally described.

The two mesic grassland associations described here are clearly part of (possibly remnants of?) the Highveld grasslands ecoregion in Souh Africa (Bowie and Frank 2001; Olson et al. 2001; Mucina and Rutherford 2006). Yet, through the occurrence of specific species either endemic to the Otavi Mountains or not known to occur in the Highveld grasslands, these two associations are confidently described as new associations. As a comprehensive higher syntaxonomic classification of the entire grassland ecoregion of South Africa seems lacking (Mucina and Rutherford 2006), no placement in such a system could be attempted.

The general lack of syntaxonomical descriptions in neighbouring Botswana and Angola, together with a lack of a comprehensive syntaxonomic overview of especially the grassland and bushveld ecoregions in South Africa, makes a comparision of the present Namibian syntaxonomic classification to similar southern African vegetation difficult.

With 889 observed species within roughly 25,000 km2, the Karstveld is extremely species rich within the arid- to semi-arid Namibian context (Mendelsohn et al. 2002; Craven and Vorster 2006). It is comparable in richness to the Khomas Hochland in Namibia, where 914 species have been observed over roughly 31,000 km2. The Khomas Hochland, however covers a far bigger variety of habitat types along a steep rainfall gradient (Strohbach 2021). As this survey was only on a reconnaissance scale, the actual number of species occurring here could be vastly higher. Yet only fractions of these ecosystems are formally protected within the Etosha National Park, putting a high importance on private nature reserves and conservancies within this area. Three such freehold conservancies exist, being the Otavi Mountain, Ngarangombe and Omirunga conservancies (Shaw and Marker 2010; NACSO 2022). The Karstveld plains, including the Omuramba Ovambo ecosystem, is however virtually unprotected (Shaw and Marker 2010).

Data availability

The data used for this publication forms part of the Namibian Phytosociological Database (GVID ID AF-NA-001) and can be provided on request by the corresponding author. The full relevé data is also reproduced in Appendix 1 as phytosociological table. All data of GVID ID AF-NA-001 has been shared with the sPlot database as well as the GBIF database.

Author contributions

B.S. planned the research, B.S. and M.S. conducted the field sampling, M.S. did the initial data analysis and description for the Thornbush savanna, whilst B.S. reanalysed the entire data set and drafted the manuscript. Both authors critically revised the manuscript.

Acknowledgements

Thanks is due to numerous farmers and landowners who permitted us access to their land and often pointed out interesting features of the vegetation on their property. Unknown species were identified by staff of the National Herbarium of Namibia (WIND), which is gratefully acknowledged. Soil sample analysis was done by the Agricultural Laboratory, Ministry of Agriculture, Water and Forestry, Namibia. Field data collection was co-funded from the recurrent budget of the National Botanical Research Institute, Ministry of Agriculture, Water and Forestry (Vote 2004) and the BIOTA Southern Africa project, as part of the German Federal Ministry of Education and Research (BMBF) research program “Biodiversity and Global Change” (BIOLOG) under their promotion number 01LC0024. The authors are greatful for numerous comments and corrections by unknown reviewers and the editor to improve the quality of the manuscript.

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Supplementary materials

Supplementary material 1 

Climate diagrams for several localities within the Karstveld of Namibia

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Supplementary material 2 

Phytosociological tables of the five major groupings

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Supplementary material 3 

Full synoptic tables of the five major groupings

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