Aims: There is extensive documentation of the floristic composition and plant diversity patterns in the South American coastal deserts and the adjoining arid Puna. Surprisingly, the vegetation along the transition zone from these deserts in the coastal lowlands to the Puna highlands has been little studied. The main goal of this study was to characterize and compare the structure of plant communities in two localities in the Ica department, with the aim of contributing to the floristic knowledge of the desertic western Andean slopes along the lowlands to Andean transition zone. Study area: Huancacasa and La Bolivar localities located at approximately 740 and 3,000 m a.s.l. in the Ica department, Peru. Methods: We sampled 10 plots of 100 m × 60 m located between 740–1,600 m a.s.l. in La Bolivar and 15 modified Whittaker plots (MWPs) of 20 m × 5 m located between 2,800–3,000 m a.s.l. in Huancacasa and recorded species richness and abundance. We estimated alpha diversity, performed Non-Metric Multidimensional Scaling (NMDS) and one-way Similarity (ANOSIM) analyses and plotted rank-abundance curves. Results: We recorded 215 species and morphospecies with coastal and Andean distribution, including 43 species (21.3%) that are either considered endemic to Peru or have been considered under some form of threat by Peruvian or international standards. Both plant communities differed in terms of composition, species richness, abundance, and dominant growth form, with higher values in the communities located at higher elevations. We added 83 species as new records for the Ica department. Conclusions: Our research reinforced the need to increase exploration and documentation of the vegetation within the lowland to highland transition zone along the dry western slopes of the Andes. Our results from such a transition in Ica department in southern Peru, show that much of its plant diversity seems to be, as yet, largely unknown.

Taxonomic reference: The Plant List (2013).

Abbreviations: ANOSIM = one-way Analysis of Similarities; BMAP = Biodiversity Monitoring and Assessment Program; IUCN = International Union for Conservation of Nature; NMDS = Non-Metric Multidimensional Scaling; USM = Universidad Nacional Mayor de San Marcos (Herbarium).

Andean biodiversity, Atacama, coastal desert, community structure, endemism, floristic records, mountain, southern Peru, threatened species

A major feature of the Pacific coast and western slopes of South America are the arid and semi-arid ecosystems extending from the coastal lowlands to the upper slopes of the western Andes that include the well-known Peruvian and Atacama deserts and their associated fog-oasis “lomas” (Walter and Breckle 2004; Rundel et al. 2007). At elevations above 4,000 m a.s.l., these deserts are replaced by more humid ecosystems in the North-Central Moist Andes (north of 14°S latitude) and similarly arid ecosystems prevail towards the south in the South-Central Dry Andes (Josse et al. 2003). These latter arid ecosystems include varying forms of scrub communities dominated by Cactaceae (Sarmiento 1975), before reaching the highland Puna formations starting at 3,200–3,600 m a.s.l. There is extensive documentation on the floristic composition and plant diversity patterns of coastal deserts (e.g. Luebert 2011, and references therein), which harbor important levels of plant endemism (Rundel et al. 1991; Moat et al. 2021), and the arid Puna (e.g. Luebert and Gajardo 2000; López et al. 2006; Montesinos et al. 2012, 2015a). Surprisingly, the vegetation along the transition zone from the deserts in the coastal lowlands to the Puna highlands has been little studied (but see Galán de Mera et al. 2009 and Chicalla-Rios 2021). Phytogeographically, these dry western slopes of the Central Andes have been linked to both the desert and the Puna (Sarmiento 1975), although Rundel et al. (2007) suggested they had closer affinities with the Puna vegetation.

Studies of the flora and vegetation of the coastal desert in Peru have focused on the hills and coastal wetlands (Johnston 1931; Weberbauer 1945; Ferreyra 1953, 1962, 1983, 1993; Müller 1985; Rundel et al. 1991; León et al. 1996; Galán de Mera et al. 1997, 2003, 2010; Cano et al. 1999; Dillon et al. 2011). Additionally, there have been efforts to document the flora on the south coast of the country (Dillon 1997a, 1997b; Arakaki and Cano 2003; Leon et al. 2004; Galán de Mera et al. 2009; Montesinos and Mondragón 2013; Quipuscoa et al. 2016). The department of Ica has received particular attention (León et al. 1997; Roque and Cano 1999; Cano et al. 2005; Jiménez et al. 2008) and the Catalogue of the flowering plants and gymnosperms of Peru published in 1993 recorded only 149 species for the entire department (Brako and Zarucchi 1993). Recent works indicate that in this department there are more than 500 species, dominated by Asteraceae, Poaceae, Fabaceae, Solanaceae, Malvaceae and Cactaceae (Whaley et al. 2010b, 2019).

Documentation of the flora of the department of Ica has concentrated mainly on the plant communities of the coastal plains, including Tillandsia mats, dry forests, dunes, riparian vegetation, wetlands, orchards, scrublands, lomas, cacti thickets and mixed xerophytic thickets with trees that support populations of epiphytic bromeliads and lichens (Whaley et al. 2019). However, the floristic composition of higher areas of the department, where the Andean mountains narrow and descend from 4,000 m a.s.l. in the Arid western Andes to the central Pacific coast at about 750 m a.s.l. has been less explored and documented, except for some phytosociological (Galán de Mera et al. 2003, 2004, 2009) and floristic studies (Whaley et al. 2019). Together, all these studies show that despite being considered as a desertic region, the department of Ica is home to a considerable number of species of the Peruvian flora, including several endemics and threatened species (León et al. 2006; Ministerio de Agricultura y Riego 2006). In this context, there remains important botanical knowledge gaps in the department of Ica (Roque and Cano 1999). This situation is exacerbated by the fact that several species and ecosystems in Ica are threatened by the combined effect of urban expansion, pollution, overgrazing and climatic changes (Beresford-Jones et al. 2009).

Within the framework of a Biodiversity Monitoring and Evaluation Program (BMAP), a collaboration between the Smithsonian Institute and the PERU LNG company in the southern coast and highlands of Peru, we had the opportunity to study the vegetation of the western slopes of the department of Ica (Dallmeier et al. 2013). Although the BMAP was initially only focused on gathering information on the population ecology of Cleistocactus acanthurus and C. hystrix (Cactaceae), the study was later extended to document the accompanying vascular plant communities. The present contribution provides a general overview of the desert flora in the western Andean slopes of southern Peru and compares vegetation characteristics, diversity, and community structure between two locations along the elevation gradient.

The department of Ica is located in the central coast of Peru and is dominated by an extensive desertic coastal plain adjacent to the Pacific Ocean (Whaley et al. 2010b) that receives less than 8 mm annual rainfall (Dávila et al. 1981; Olivares et al. 1994). Further inland the landscape is dominated by the dry western slopes of the Andes, transitioning from desert to cacti woodlands at lower and middle elevations (750–3,100 m a.s.l.) and then rapidly ascending to the dry Puna at higher elevations (above 4,000 m a.s.l.). Our study focused on two locations along these dry western slopes (Figure 1).

La Bolívar (740–1,790 m a.s.l., Figure 2), is located adjacent to the sand plains of the province of Pisco (13.73°S, 75.75°W). It belongs to the thermotropical belt of southern Peru (Galán de Mera et al. 2017), and according to its elevation has a per-arid and semi-warm climate with an annual average of 80 mm of precipitation (Olivares et al. 1994). Temperature varies between 17 °C to 24 °C (Olivares et al. 1994), with an annual mean of 19.4 °C (free CHELSA data set 1981–2010, Karger et al. 2017) and a relative humidity of 78% (Olivares et al. 1994). It constitutes the lower slopes of the western Andes characterized by heavily dissected hills that intersect with moderately dissected streams (Langstroth et al. 2013), formed by semi-consolidated heterometric and heterogeneous alluvial and fluvial deposits of medium to high permeability (Olivares et al. 1994). Ecologically, it corresponds to the Pre-Montane Desert and Pre-Montane Desert Scrub formations, containing cacti such as Neoraimondia arequipensis and Armatocereus procerus along with some seasonal herbs and shrub deciduous species such as Orthopterygium huaucui, Cnidoscolus basiacanthus, and Bulnesia retama (Figure 2, Whaley et al. 2010a).

The second area, Huancacasa (2,600–3,000 m a.s.l., Figure 3), is located higher up of the western Andean slopes that border the Huancavelica department (13.73°S, 75.51°W). It belongs to the mesotropical belt (Galán de Mera et al. 2017), and according to its elevation has a semi-arid and temperate climate with an annual average of 380 mm of precipitation (Olivares et al. 1994), an annual mean temperature of 11.3 °C (free CHELSA data set 1981–2010, Karger et al. 2017) and a relative humidity of 67% (Olivares et al. 1994). It is characterized by hills and ridges that form the division between the upper part of the San Juan and Murcielago creeks, that are crossed by a large number of minor streams that change the physiography of the relief making it less rugged (Langstroth et al. 2013). Ecologically it corresponds to the Lower Montane Thorny Steppe formations with mostly ephemeral vegetation with annual species such as Glandularia sp., Tarasa operculata, Heliotropium sp., Senecio sp. and Trixis cacalioides, together with dispersed columnar cacti such as Armatocereus matucanensis, Browningia candelaris, Corryocactus brevistylus subsp. puquiensis and Weberbauerocereus rahuii (Figure 3, Arenas and Fernandez 2009).

Figure 1. 

Plot location and codes in the study area, showing the two main natural ecosystems (coastal desert and Andean shrubland), as well as agricultural areas restricted to valleys. Framed area in inset shows location of study area in Peru.

Figure 2. 

Landscapes in La Bolivar (images A and B) and representative species. C. Orthopterygium huaucui; D. Neoraimondia arequipensis; E. Cleistocactus acanthurus; F. Armatocereus procerus.

Figure 3. 

Landscapes in Huancacasa (images A and B) and representative species: C. Cleistocactus hystrix; D. Cumulopuntia sphaerica; E. Erodium cicutarium; F. Tarasa operculata.

To record the composition and abundance of the vegetation we sampled both localities during the months of February and March 2014. We surveyed 10 plots of 100 m × 60 m located between 740–1,600 m a.s.l. in La Bolivar (Novoa and Mendívil 2011; Novoa and Vega 2013) and 15 modified Whittaker plots (MWPs) (Barnett and Stohlgren 2003) of 20 m × 5 m located between 2,800–3,000 m a.s.l. in Huancacasa (Table 1). Plots were originally installed to monitor cacti populations only (Novoa and Mendívil 2011), with surveys of the associated vegetation added in 2014. Consequently, the differing plot sizes responded to differences observed in cacti abundances in each locality in our original research protocol (lower cacti abundances and density in La Bolivar required bigger plots to survey equivalent populations). Site accessibility and logistics were the main factors for site selection for each plot, followed by topographic position and slope. Where possible, we chose plots at the bottom of the valley, slope, and ridge in each locality. Vegetation physiognomy was visually homogeneous within each plot. Species abundance within each plot was measured as the number of individuals per plot. Inserting our coordinates per plot in the free CHELSA data set 1981–2010 we obtained mean annual temperature and annual precipitation (Karger et al. 2017). Elevation was recorded in the field and landform was assigned using the Topographic Position Index tool in QGIS (QGIS.org 2001). This tool calculates the index by comparing the elevation of each data point to its surroundings (Guisan et al. 1999). Points higher than their surroundings have a positive index value, for example ridges and hilltops. The value is negative for areas like valleys. Values of this index are then categorized into ten different landforms (Jenness 2006).

Given collection restrictions in the area due to the presence of natural populations of threatened and CITES species such as Cleistocactus acanthurus and C. hystrix, we followed collecting guidelines issued by the Peruvian National Forest Service Nacional Forestal (SERFOR) as per our permit and took a minimum-sampling approach by collecting only species that could not be identified unambiguously in the field, with three duplicates per species, following conventional herbarium procedures (Sánchez-González and González 2007). All collections were deposited in the USM Herbarium (National History Museum of the San Marcos National University). Since conditions of extreme aridity did not always allow the collection of complete material for herbarium deposition, we also chose to register species using photographic material where possible.

Based on the quantitative survey in 2014 and several site visits between 2014–2019 (allowing us to record specimens within and outside of the survey plots) we assembled a list of species and morphospecies for the two locations. We used the morphospecies concept on collections that were difficult to identify at species level, but otherwise had morphological characters that unequivocally differed from all the other material already identified in our study. We followed APG IV (Angiosperm Phylogeny Group 2016), scientific names and authorship were confirmed by consulting The Plant List (2013). Growth form followed Pérez-Harguindeguy et al. (2013) and was determined in the field and by consulting TROPICOS (Missouri Botanical Garden 2020). Each species was assigned to an herbaceous, shrub, stem succulent and climber growth form. Elevation range and region were also determined by consulting TROPICOS (Missouri Botanical Garden 2020), by following the geographic regionalization of Brako and Zarucchi (1993) and contrasted with published literature for Peru. International and national conservation status followed IUCN (2020) and Ministerio de Agricultura y Riego (2006), respectively. Endemism assessment followed León et al. (2006) and was restricted to Peru. We considered records to be new for Ica, when they had not been reported previously in the region by Brako and Zarucchi (1993), León et al. (2006), Whaley et al (2019), or any other published work citing voucher specimens from Ica. An additional group of species was considered as potential new records since their taxonomic status is not yet fully confirmed (specimens tentatively labeled as aff. or cf., pending collection and revision of additional material). This latter group was excluded from further analyses, except for Oldenlandia as it represents a new genus for Ica.

Our research reinforces the need to increase exploration and documentation of the vegetation along the dry western slopes of the Andes (with an emphasis on the transition zones from the deserts in the coastal lowlands to the Puna highlands). Particularly we found that: (1) there is an important number of species inhabiting the western slopes of the Andes, many of them endemics (2) there is a different floristic composition between localities and, (3) species richness and abundance increase as elevation rises.

Overall, our results indicate that more than 74% of the species recorded in this study are typical of coastal-Andean ecosystems. Furthermore, they suggest that the Andean slopes of the department of Ica are harboring an important percentage of the diversity of the dry western slopes of the Andes along the coast to highlands transition, including endemic and threatened species. Whaley et al. (2019) estimated the regional flora of Ica to be between 550 to 650 vascular plant species. The new records we report here bring the flora of Ica to 583 species, well within this range. Additional surveys and collections may reveal more about the distribution of species that are considered endemic for some departments, extending their range, and updating their conservation status. The quantitative data reported here show that several species were local or regionally rare, suggesting that a revision of their national or international threat assessment category is needed. This is especially relevant for the island-like vegetation patches that characterize the lomas, cactus and scrub habitats within the Ica desert, each of which can hold unique plant assemblages (Rundel et al. 1991). Furthermore, the interface between the deserts in the coastal lowlands to the Puna highlands, where our study area was situated, is an area that seems to have been subjected to similar ecological divergence and ecogeographical isolation factors as reported for coastal deserts further south (Ruhm et al. 2020). These conditions, the scant floristic and vegetation studies in these habitats, and the number of remaining unidentified material (which we have been unable to adequately sample and identify despite ongoing visits to our study area) and species that are awaiting taxonomic confirmation included as cf. and aff. suggest that there are several taxa that will be added in the future.

Plot-based species abundance data have been deposited at Figshare and are publicly available (https://doi.org/10.25573/data.13624055.v3). All other data used and mentioned in the manuscript are provided as Suppl. materials 1–7.

R.L.P designed the study, N.V conducted the field sampling, R.L.P and A.M.H performed the statistical analyses, A.M.H led the writing, while all authors critically revised the manuscript.

This study was possible due to financial and logistic support from PERU LNG as part of the Biodiversity Monitoring and Assessment Program, a research agreement between PERU LNG and the Smithsonian Conservation Biology Institute. We especially thank Bruno Vildoso and Carolina Casaretto (both PLNG) and Ornella Sissa and Karim Ledesma (both SCBI) for supporting the expeditions. We thank Catherine Bravo, Héctor Chuquillanqui, Elias Mendivil, Pablo Najarro, Sidney Novoa and Marco Rivera for support during fieldwork. Research permits Resolución de Dirección General N°: 0044 2014-SERFOR-DGGSPFFS, 075-2015-SERFOR-DGGSPFFS, 281-2017-SERFOR-DGGSPFFS and 431-2018-MINAGRI-SERFOR-DGGSPFFS were issued by the Peruvian Forest Service (SERFOR). This is contribution No. 64 of the Peruvian Biodiversity Program of the Smithsonian Conservation Biology Institute.

• Angie Montenegro-Hoyos (Corresponding author, angie.carol@userena.cl), ORCID: https://orcid.org/0000-0002-8685-3666
• Nanette Vega (naveve2004@yahoo.es), ORCID: https://orcid.org/0000-0001-8538-0409
• Reynaldo Linares-Palomino (LinaresR@si.edu), ORCID: https://orcid.org/0000-0002-7631-5549