Corresponding author: Anna Kuzemko ( anyameadow.ak@gmail.com ) Academic editor: Monika Janišová
© 2021 Viktor Shapoval, Anna Kuzemko.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Shapoval V, Kuzemko A (2021) Syntaxonomy of steppe depression vegetation of Ukraine. Vegetation Classification and Survey 2: 87-108. https://doi.org/10.3897/VCS/2021/62825
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Aims: To revise the syntaxonomy of the vegetation of steppe depressions (pody), in particular (1) to identify the associations and to reveal their environmental, structural and compositional peculiarities; (2) to assign the associations to higher syntaxa; and (3) to correct nomenclatural aspects according to the ICPN.
Study area: Steppe zone of Ukraine, Left-Bank of the Lower Dnieper basin.
Methods: 641 relevés were included in the final analysis in the PCOrd program integrated into Juice software. Two expert systems (EVC and EUNIS-ESy) were used to assign relevés to vegetation classes and to EUNIS units.
Results: The analysis resulted in nine clusters, which were interpreted as Festuco-Brometea (two units), Molinio-Arrhenatheretea (three units), Isoёto-Nanojuncetea (three units) and one derivate community of the Festuco-Puccinellietea. Detailed characteristics of the species composition, structure, distribution, and environmental conditions are provided for each unit. According to the DCA ordination, the leading factors of the syntaxa differentiation are soil moisture and fluctuating water level.
Conclusions: We could clarify the placement of steppe depression vegetation in the system of syntaxonomic units of Europe. The previously described syntaxa of the rank of alliance (Myosuro-Beckmannion eruciformis), suballiance (Galio ruthenici-Caricenion praecocis), and six associations are validated. Two associations and two subassociations are described as a new to science.
Taxonomic references: Euro+Med PlantBase (https://www.emplantbase.org), except
Syntaxonomic references:
Abbreviations: DCA = Detrended Correspondence Analysis; DES = Didukh Ecological Scales; EUNIS = European Nature Information System; EVC = EuroVegChecklist; GIVD = Global Index of Vegetation-Plot Databases; ICPN = International Code of Phytosociological Nomenclature.
Althaeion officinalis, Bern Convention, Didukh ecological scales, EUNIS, expert system, grasslands, Myosuro-Beckmannion eruciformis, steppe depressions, syntaxonomy, wetlands
Steppe depressions (pody in Ukrainian) are large closed depressions, up to 16,000 ha in area, elliptical or round in shape with gentle slopes and flat bottoms, periodically flooded by meltwater and characterized by Planosol soils and peculiar ephemeral mesic to wet grassland phytocenoses. These depressions accumulate natural runoff in poorly drained steppe plains within the periglacial area of the Quaternary glaciation. In Ukraine, the largest depressions are concentrated on the Left Bank of the Lower Dnieper (Kherson and Zaporizhia administrative oblasts), while sporadic, smaller depressions and steppe “saucers” occur on the Right Bank of the Dnieper (Kherson, Mykolaiv, rarely Odessa oblasts). In the Russian Federation, similar depressions are common in the Lower Don River and Lower Volga River regions (
Following the flooding of depressions, over the entire area of the shallow basin, there is an “explosive” formation of ephemeral hydrophilic cenoses. They exist for a short period, being rapidly replaced by xeromorphic flora and finally become steppic when the depression dries. The average duration of the period between severe floods is, according to various estimates, from 7 to 12 years (Shapoval and Zvegintsov 2010). During periods of flooding and subsequent drying, distinctive alternating phytocenoses with wide ecological amplitude are observed, which consist of plants that withstand drought well and «explosively» increase in number during floods, i.e. are adapted to significant fluctuations in water levels. During short-term floods, the vegetation of depressions is characterized by high values of aboveground phytomass. For example, after the floods of 2003, the average values on the hayfields of the «Black Valley» depression was 12892 ± 518.0 kg/ha in the dry state. However, these values decline rapidly during periods of drought. Also, their productivity decreases due to overgrazing. In particular, in the post-flood period, the value of aboveground phytomass of the adjacent intensively grazed «Sugakli» depression was only 912 ± 239.2 kg/ha, which is significantly less than similar values of hayfields with better moderate grazing management. In general, the stocks of aboveground phytomass in the studied pody under different landuse regimes vary in a wide range from 588 to 14788 kg/ha in the dry state (
Vegetation types of depressions are separated in time and space, as actual phytocenoses are scattered territorially (some are confined to the deepest, wettest areas of a depression bottom, others tend to its dry periphery), and they are delimited in time (open water surface overgrown with wetland vegetation, which is later replaced by mesic and semi-dry grasslands). At the same time, the boundaries between these phytocenoses are often blurred, and the spatial transitions among them are very gradual.
The problem of the origin of the depressions still has no unambiguous solution; many issues remain problematic and debatable. During the long history of studying the loess cover of the lowland steppes of the Southern Ukraine, many hypotheses and theories of the origin of steppe pody have been put forward. They were considered as remnants of the ancient hydrographic network (
Unfortunately, in Ukraine most of the steppe depressions are plowed, and the surviving remnants are exploited, mainly as hayfields and pastures without compliance with rational management standards, including nature conservation. The only steppe depression that has a national conservation status is the Great Chapelsky pid, as part of the natural core of the Biosphere Reserve «Askania-Nova» (2,376 hectares). Steppe depressions are the sole localities of local and regional endemics in the region of the Left Bank of the Lower Dnieper (Elytrigia repens subsp. pseudocaesia, Phlomis scythica, Tulipa scythica).
The syntaxonomy of these unique complexes is still poorly known and needs to be thoroughly revised. The first attempt to develop a classification of the steppe depression vegetation was made by a team led by Solomakha (
Adding to syntaxonomic incertainty, in the recently published Prodromus of Vegetation of Ukraine (
The above review has shown that many questions remain unresolved in the syntaxonomy of the steppe depression vegetation. And the biggest, quite objective problem of syntaxonomic analysis of pody vegetation is the availability of representative data because the object of study is quite ephemeral. The precondition for its occurrence is a flood. Due to the exceptional rarity of this phenomenon, it is possible to observe and describe the pody phytocenoses in very limited periods of time, and the interval between the favorable seasons for the mentioned ephemeral vegetation can be decades. Only after the major flooding in 2010 was sufficiently representative data for the current analysis available for collection.
Given this, our aim was to revise the syntaxonomy of the steppe depressions (pody) vegetation, in particular (1) to identify the associations and to reveal their environmental, structural and compositional peculiarities; (2) to assign the associations to higher syntaxa; and (3) to correct nomenclatural aspects according to the ICPN.
In accordance with the modern administrative-territorial structure of Ukraine, the studied pody are located within Kakhovka and Henichesk districts of Kherson oblast and Melitopol district of Zaporizhia oblast. Great Chapelskyi pid, as well as Staryi pid and a number of small depressions within “Southern” site are components of the natural core of the Askania-Nova Biosphere Reserve (Figure
In accordance with the Worldwide Bioclimatic Classification System the study area is located on the border of Temperate xeric steppic and Mediterranean pluviseasonal continental steppic variants, Supra-submediterranean and Supramediterranean variants within the Dobrujo-Crimean subregion of the Eurosiberian biogeographic region (
According to the agro-meteorological station Askania-Nova, the average annual temperature is 11.3°С. The average annual precipitation is 400 mm. Most precipitation (37% of the annual amount) falls in the summer in a form of showers and short-term rains. During the period of moisture accumulation (November-March) the amount of precipitation does not exceed 100 mm. Evaporation is 900–1000 mm, and in the summer months it exceeds precipitation by 5–7 times (Figure
Depressions in lowland steppes are represented by two structural and genetic forms – steppe saucers and pody. Steppe saucers are small, with depth up to 0.5 m and diameter 2–150 (up to 600) m. Their density is 30–120 saucers per 1 km2, depending on erosional dissection and inclination of the terrain. Almost all of them are plowed today. Depressions with a depth of 3–5 (sometimes 10–15) m and a total area of more than 1 ha (up to 16,000 ha), with erosive slopes, catchment basins and flat bottoms represent the second group of depressions – pody. In the interfluve of the Dnieper and Molochna rivers, small depressions with a diameter of up to 1000 m and a depth of about 0.5–3 m are common. Most of depressions are plowed due to their easy accessibility; pristine vegetation is preserved only in the small depressions within the territory of the Biosphere Reserve «Askania-Nova». Other interfluve pody have significant size (see Table
In general, pody is a key typological unit of macro- and mesorelief forms of the Steppe zone, and expresses the geomorphological, hydrographic, edaphic, and biotic identity of the whole catchment. The actual concept of steppe depressions (pody) means a complex formation, which includes the following elements: a bottom (perfectly flat surface delineated by the lowest closed horizontal), the slopes, which form a closed depression bowl (its sides) and, finally, the estuaries of a ravine catchment, cut into the general slopes (Shapoval and Zvegintsov 2010) (Figure
The most common and typical soils of the studied region are Luvic Planosol or gleyosolod in the traditional Ukraininan soil classification (
There are two seasonal types of depression flooding: winter-spring, caused by melting snow during thaw, and extremely rare summer-autumn – caused by heavy rains (
Currently, due to the over-regulation of the catchment area, with much plowing and crossing by various communications (water supply canals, highways, etc.), the frequency and duration of floods have decreased significantly, causing xerophytization of these habitats. Modern heavy floods begin in February and last until the beginning of June (the last small puddles in the depths of the bottom may last until the end of July). The area of flooding can reach 3–4 thousand hectares with the water depth up to 20–40 cm in the center of the depression.
Polygenetics, different sizes, differentiation of microrelief and soil cover of depressions together with sporadic hydrogenic fluctuations, historical and current management determine the nature and dynamics of their vegetation. In fact, it is a unique dynamic complex of hydro-, meso- and xeromorphic communities, which, of course, complicates its study.
Name | Coordinates of the conditional central point | Administrative location | Preserved area (pristine land and perennial fallows), hectares | Size (bottom and slopes forming a closed «bowl» of the depression), km | Protection |
---|---|---|---|---|---|
Great Chapelsky | 46°29'04.7"N 33°51'01.9"E | near Askania Nova, Kakhovka district, Kherson oblast | 2376 | 4,5×6 | natural core of the Askania-Nova Biosphere Reserve |
Staryi | 46°27'25.2"N 33°55'06.4"E | near Askania Nova, Kakhovka district, Kherson oblast | 140 | 0.3×0.5 | natural core of the Askania-Nova Biosphere Reserve |
Series of nameless small depressions | 46°27'55.7"N 34°00'26.0"E | near Askania Nova, Kakhovka district, Kherson oblast | up to 300 (in total) | – | natural core of the Askania-Nova Biosphere Reserve |
Small Chapelsky | 46°25'40.3"N 33°43'52.2"E | outskirts of Khrestivka and Dolynske villages, Kakhovka district, Kherson oblast | 1022 | 5,5×6,5 | Emerald site UA0000372 |
Barnashivsky | 46°32'50.3"N 33°58'38.3"E | near the Maryanivka village, Kakhovka district, Kherson oblast | 738 | 2.5×4 | Emerald site UA0000367 |
Chorna Dolyna (Black Valley) | 46°33'15.1"N 33°28'26.4"E | near the Chorna Dolyna village, Kakhovka district, Kherson oblast | 494 | 3×6 | Emerald site UA0000368 |
Zeleny (Green) | 46°40'15.1"N 33°43'01.8"E | outskirts of Zeleny pid and Zelena Rubanivka villages, Kakhovka district, Kherson oblast | 1580 | 5,5×8 | Emerald site UA0000370 |
Podivsky | 46°39'51.7"N 33°49'32.4"E | near Podivka village, Kakhovka district, Kherson oblast | 258 | 1.5×2.4 | – |
Garbuzy | 46°46'07.2"N 34°03'13.6"E | near Stepne village, Henichesk district, Kherson oblast | 152 | 1.2×1.7 | Emerald site UA0000383 |
Ahaimansky | 46°40'13.8"N 34°11'36.0"E | near Ahaimany village, Henichesk district, Kherson oblast | 4849 | 10×16 | Emerald site UA0000366 |
Koianly | 46°41'24.6"N 34°28'56.6"E | near Shotivka village, Henichesk district, Kherson oblast | 148 | 5,5×11 | – |
Domuzlynsky | 46°36'14.1"N 34°43'43.4"E | near Zeleny Hai village, Henichesk district, Kherson oblast and Trudove village с. Трудове, Melitopol district, Zaporizhzhia oblast | 4743 | 9×13 | Emerald site UA0000369 |
Novotroitsky | 46°19'09.7"N 34°21'37.4"E | near Novotroitse urban village, Henichesk district, Kherson oblast | 97 | 3.5×4 | – |
Syvasky | 46°20'56.5"N 34°31'45.4"E | Near Syvaske village Henichesk district, Kherson oblast | 1549 | 6×8,5 | Emerald site UA0000371 |
The materials for the study were 1897 vegetation plots made by V.V. Shapoval, O.P. Goffman, N.Y. Drohobych, N.A. Dotsenko, N.S. Shestakova, A.A. Kuzemko and I.I. Moysienko in the depressions of the Steppe zone of Ukraine in the period from 1967 to 2019. Plots are stored in the Turboveg format (
Since the aim of our work was the syntaxonomic analysis of mesic and wet communities of steppe depressions, we deliberately removed from the analysis all vegetation plots of typical steppes, which according to a preliminary phytoindication assessment received an average score 7 or less on the moisture scale based on the DES (
As a result of the classification, we obtained nine units (Table
Distribution. Small shallow depressions of the natural core of the Askania-Nova Biosphere Reserve.
Environmental conditions. Communities characterized by clear signs of succession with accumulation of a thick litter. The territory is kept in a completely protected regime (‘absolut zapovednost”). Here, the ecosystem is not grazed by wild ungulates which contributes to growth of vegetative-mobile mesophytic species and impoverishment of phytodiversity. Soils are meadow-chestnut gleyed sweetened and gley-sweet Planosol. These small depressions are almost not flooded, although they usually have better moisture conditions compared to the adjacent steppe. Sometimes during snowy winters, there may be short-term puddles on the bottoms in February-March, but heavy floods are not observed and the water completely disappears before the period of active vegetation.
Structure and composition. Total cover varies in a wide range – from 19 to 100%, an average of 75,3%, litter – from 5 to 70%. In general, phytocenoses are quite dynamic and are characterized by various combinations of mesomorphic rhizome species and rotations of their coenotic positions depending on different changes in the environment. Dominant species are Bromopsis inermis, Elytrigia repens, Carex praecox, Poa angustifolia, rarely Bromopsis riparia (Figure
Distribution. Small depressions of the natural core of the Askania-Nova Biosphere Reserve and sporadically on the slopes and dry bottom of the Great Chapelsky pid.
Environmental conditions. Communities are mostly localized along the bottom edge and at lower slopes (on the verge of flooding) or in local depressions, surrounded by more xerophytic phytocenoses, so they occur in depressions with preserved slopes and adjacent pristine steppe. During strong floods they give way to more hydrophytic communities; during severe droughts they are in a depressed state, lose hygromesophytic elements, and are replaced by more dry communities. The conditions of this association are perfectly suited to Carex melanostachya, which can resist extreme changes in moisture conditions, growing both in a dry steppe and among ephemeral shallow-water vegetation.
Structure and composition. The total cover varies in a wide range from 40 to 100%, occasionally 10–25%, on average 73%. Communities are more mesophytic than the Ferulo-Caricetum praecocis, which is manifested primarily in the strong phytocenotic position of the dominant Carex melanostachya and Elytrigia repens subsp. pseudocaesia, increase in the occurrence and total proportion of Alopecurus pratensis, presence of Eryngium planum (which tends in the Ascanian steppe to depressions with saline soils and sufficient moisture) as well as Hypericum perforatum, Veronica spicata, V. barrelieri, Gagea transversalis, Euphorbia esula subsp. tommasiniana, Ferula euxina and Rumex crispus, and sometimes a significant admixture of annual plants, confined to short-term wetlands (“saucers”, puddles), namely Gypsophila muralis, Cyperus flavescens, Myosurus minimus and Rorippa brachycarpa and Phalacrachena inuloides as characteristic element of the mesophytic forbs of steppe depressions. Another typical mesophytic species of these communities is Sibbaldianthe bifurca subsp. orientalis, which is found in watershed hollows and depressions with semi-dry or mesic grassland vegetation. Thus, the phytocenoses of this unit show a more mesomorphic character, although they are accompanied by many xerophytic steppe elements (Seseli tortuosum, Euphorbia seguierana, Sisymbrium polymorphum, Festuca valesiaca, F. pseudovina, Agropyron cristatum subsp. pectinatum, Phlomis herba-venti subsp. pungens, and very rarely Stipa capillata and S. ucrainica), which generally reveals the mixed, transition nature of these communities.
Distribution. Peripheral part of the Great Chapelsky pid bottom.
Environmental conditions. The territory is grazed by wild ungulates, mostly in a state of modest overgrazing.
Structure and composition. Litter is almost absent. Sometimes, where there is considerable aboveground phytomass, strands of coarse dry biomass from common rhizome grasses can be present. Total cover of herb layer is 70–100% (average 80.3%). Phytocenoses are characterized by an absolute dominance of rhizome-turf mesophytic grass Alopecurus pratensis (Figure
Long-term grazing regime of this community leaves an imprint on the structure of herb layer and is marked by a significant participation of Artemisia austriaca (the number of individuals increases markedly in dry periods with increasing grazing pressure), Poa bulbosa, Capsella bursa-pastoris, Cardaria draba, Polygonum aviculare, Senecio vernalis, Lactuca serriola, L. tatarica, Lamium amplexicaule, Erodium cicutarium, Euphorbia esula subsp. tommasiniana, Taraxacum sect. Taraxacum etc. However, trampling and fragmentary exposure of soil contributes to spreading of many annual plants including Trifolium retusum, Arenaria leptoclados, Cerastium pumilum, Crepis ramosissima, Cruciata pedemontana, Draba verna, Medicago minima, Myosotis stricta, Veronica arvensis etc. In general, these phytocenoses are characterized by low floristic richness and insignificant physiognomic variability due to an admixture of meadow forbs, and dominance of Alopecurus pratensis.
Distribution. Slopes and dry bottoms of Zeleny, “Black Valley”, Ahaimansky, Garbuzy, Small Chapelsky pody, nameless depressions from the outskirts of the village Podivka and the village Novotroyitske, on the slopes of the Great Chapelsky pid, as well as known from old relevés (1970s) from the natural core of the Biosphere Reserve «Askania-Nova» («Southern» site). Today, due to reservogenic succession (i.e. succession caused by the protected regime of the territory, with an unbalanced or incomplete structure), accompanied by the accumulation of abundant litter, these phytocenoses have disappeared from the «Southern» site and are replaced mainly by monodominant communities of Poa angustifolia belonging to cluster 1.
Environmental conditions. This vegetation unit includes the most common phytocenoses, distributed in dry small depressions and in concentric strips on non-flooded edges of major depressions, which are used as pastures and periodic hayfields (under favorable vegetation conditions). Communities are confined to meadow-chestnut residual saline sweetened gley heavy loam soils. At the same time, they are characterized by a relatively stable floristic composition, which in general is maintained in scattered depressions with a similar landuse regime.
Structure and composition. Total cover varies from 25 to 95%, averaging 78.4%. Dominants are Poa angustifolia, Elytrigia repens subsp. pseudocaesia, Ventenata dubia, Artemisia santonicum and A. austriaca, in some places Festuca valesiaca, Alopecurus pratensis, Carex praecox and C. melanostachya. Extremely bright and colorful aspects are formed by the large and coenotically strong contribution of forbs (Figure
The heterogeneous nature of these communities is visualized by the combination of xeromorphic plants, such as Festuca valesiaca, F. рseudovina, Koeleria macrantha, Limonium sareptanum, Medicago romanica, Ventenata dubia, Polycnemum arvense, Filago arvensis, Seseli tortuosum with hydrophilic species like Butomus umbellatus, Elatine alsinastrum, Eleocharis palustris, E. uniglumis, Gratiola officinalis, Lythrum virgatum, Plantago tenuiflora, Pulicaria vulgaris, Rorippa austriaca, occasionally Beckmannia eruciformis.
Finally, the condition and structure of the communities are significantly affected by grazing, which is manifested in sporadic distribution of Ambrosia artemisiifolia, Artemisia austriaca, Cardaria draba, Centaurea diffusa, Consolida orientalis, Descurainia sophia, Eryngium campestre, Euphorbia esula subsp. tommasiniana, Polygonum aviculare, Tripleurospermum inodorum, Xanthium orientale subsp. riparium, etc.
In general, these phytocenoses are relatively open, so in between beds of grasses, it is easy to see the whitishdusty dried soil with iron-manganese nodules (beans) common on the surface, sometimes quite large (up to 1.5–2 cm in diameter, 20–30 pcs./m2).
Distribution. Along the edge of Ahaimanskyi pid bottom, including the old fallows, which were plowed in inter-flood periods. Sporadic spots and rather large closed massifs are observed in the lower part of the catchment basins and in the northern part of the Great Chapelsky pid bottom.
Structure and composition. Sparse communities with a total cover of 50–90% (average 66%), with three herbal layers. The first layer is formed by tall Elytrigia repens subsp. pseudocaesia and Rumex crispus, sporadically Armoracia rusticana, Lythrum virgatum, Schoenoplectus lacustris and Butomus umbellatus (in the first stages of post-hydrogeneous succession). In the second layer Phalacrachena inuloides prevails (Figure
Distribution. Large depressions during heavy flooding (Ahaimansky, Domuzlynsky, Great Chapelsky, Zeleny pody).
Environmental conditions. These communities have a fluctuating nature. The ecological optimum is realized during severe floods and in the short post-hydrogenous period.
Structure and composition. Phytocenoses are formed by polycarpic biomorphs and hemicryptophytes, which are dominants (predominate numerically or by mass) and edificators (determine the structure and functioning of the community, form a specific environment); namely, Beckmannia eruciformis, Gratiola officinalis, Elytrigia repens subsp. pseudocaesia, Lythrum virgatum etc. The proportion of therophytes is 60–80%. These syntaxa are related to the previous cluster 5, but are more hydrophilic and tend to more wet habitats.
The total cover varies in the range of 65–97%, averaging 82.2%. Litter is not developed – up to 4%, sometimes 1020%, due to soaked strands of the previous year’s vegetation that floated with the flowing water. Phytocenoses are distributed sporadically in local concavities of the bottom, sometimes merging into large integral massifs, characterized by distinct layers and sparse synusia. The first layer is dominated by perennial hemicryptophytes and cryptophytes: the characteristic dominant Beckmannia eruciformis (cover up to 80%), Elytrigia repens subsp. pseudocaesia, Lythrum virgatum, Schoenoplectus lacustris, occasionally Alopecurus pratensis (Figure
Due to combined mowing and grazing land-use in the «Black Valley» pid, synanthropic elements are abundant: Aegilops cylindrica, Ambrosia artemisiifolia, Centaurea diffusa, Erigeron canadensis, Lactuca serriola, L. tatarica, Plantago major, Polygonum aviculare, Xanthium orientale subsp. riparium.
Distribution. Large depressions: Great Chapelsky, Ahaimanskyi, Zeleny, “Black Valley” pody.
Environmental conditions. Hydrophilous coenoses formed during heavy flooding. Concentrated in local concavities and furrows, or occurs sporadically in the depression bottoms.
Structure and composition. Total cover is 35–97%, in average 78.7%. Quite diverse, mosaic communities with a wide range of dominants and codominants, and combined in different variants based on the forms of microrelief, soil disturbances, and degree of flooding: Butomus umbellatus, Schoenoplectus lacustris, Elytrigia repens subsp. pseudocaesia, Eleocharis palustris, E. uniglumis, Cyperus flavescens, sporadically in dry places Inula britannica (Figure
Distribution. Phytocenoses of the Great Chapelsky pid with the presence of rare species Damasonium alisma (Figure
Environmental conditions. Phytocenoses of the subassociation tend to occur in shallow water, often with open water gaps. In general, the described phytocenoses are extremely rare and exist ephemerally, with an exceptionally favorable flooding regime. In insufficiently wet seasons, such hydrophilic communities are transformed into mesic grasslands, preserving the core of dominant plants that are able to resist of moisture deficiency. But a whole complex of water demanding ephemeral species of depression disappear and are replaced by the more resistant mesophytic species.
Structure and composition. Total cover varies in the range of 65–97%, averaging 87.5%. The first herbal layer is formed by tall dominants and edificators, generally typical for bottom of depressions during periods of flooding: Elytrigia repens subsp. pseudocaesia and Lythrum virgatum with an admixture of Beckmannia eruciformis, Alopecurus pratensis, Butomus umbellatus, Rumex crispus, Poa angustifolia and Juncus atratus. The second layer is composed of dominants Eleocharis palustris, Carex melanostachya and Gratiola officinalis, with a significant proportion of Euphorbia esula subsp. tommasiniana, Phlomis scythica and sporadically Inula britannica, Rorippa austriaca, Phalacrachena inuloides. Finally, as the water recedes the damp soil is covered by Damasonium alisma, Rorippa brachycarpa, Elatine alsinastrum, rarely Elatine hungarica, Lotus angustissimus, Lythrum thymifolia, Lythrum borysthenicum, Myosurus minimus, Pholiurus pannonicus, Plantago tenuiflora, Polygonum aviculare (due to trampling), Potentilla argentea (numerous seedlings and juveniles), Gypsophila muralis, Cyperus flavescens. Sometimes, under optimal moisture conditions, Damasonium alisma reach 40–60 cm in height and extends into to the second layer.
Distribution. Great Chapelsky pid.
Environmental conditions. Fragmentary cenoses, confined to the trampled shores of artificial watercourses, which are flooded all year round and filled with artesian water (ditches for watering wild ungulates). Localized in a narrow strip along a watercourse. Characterized by clear signs of salinity.
Structure and composition. The total cover varies from 30 to 90%. The most common species are Rumex ucranicus, Taraxacum bessarabicum, Plantago tenuiflora, Pholiurus pannonicus, Petrosimonia triandra, Myosurus minimus, Juncus bufonius, and J. compressus. On the edge of a water pool Veronica anagallis-aquatica, Ranunculus sceleratus, Persicaria maculatа grow. Due to significant trampling, species that spread include Polygonum aviculare, Plantago major, Echinochloa crus-galli, Setaria pumila, Ambrosia artemisiifolia, Lactuca tatarica, Xanthium spinosum. The most common dominants are Beckmannia eruciformis, Bolboschoenus maritimus, Eleocharis palustris, Elytrigia repens subsp. pseudocaesia, Juncus gerardii, Pulicaria vulgaris, Puccinellia distans, and sporadically Schoenoplectus lacustris.
Relief of the hydrographic network of the basin of the Great Chapelsky pid, fragment (Shapoval and Zvegintsov 2010). A: bottom, B1–B3: closed slopes of depression, B: general slopes with indented watershed hollows (D), C: ravine estuaries, F: plakor (slightly convex or almost flat elevated area); 20–32: altitudes; arrows indicate direction of the runoff (bold arrows: general regional runoff).
Synoptic table of the steppe depression vegetation. Taxa percentage frequency (constancy) and modified fidelity index (phi coefficient × 100) superscripted are shown. Species within units are arranged in descending order of fidelity index; the table shows only diagnostic species; diagnostic species with percentage frequency values more than 30% and constant species with percentage frequency more than 30% are indicated in bold.
Group No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
---|---|---|---|---|---|---|---|---|---|
No. of releves | 140 | 85 | 32 | 122 | 52 | 54 | 95 | 44 | 18 |
Bromopsis inermis | 82 71 | 7 | 31 | 1 | . | . | . | . | . |
Viola kitaibeliana | 52 55 | 25 21 | . | . | . | . | . | . | . |
Vicia villosa | 74 53 | 48 28 | 12 | 11 | 10 | 2 | . | . | . |
Elytrigia repens | 24 40 | 1 | . | 5 | . | . | . | . | . |
Lamium amplexicaule var. orientale | 17 39 | . | . | . | . | . | . | . | . |
Phlomis herba-venti subsp. pungens | 34 38 | 27 29 | . | . | . | . | . | . | . |
Salsola tragus | 16 35 | . | . | . | 2 | . | . | . | . |
Dianthus guttatus | 19 | 65 53 | . | 30 17 | . | . | . | 5 | . |
Thesium arvense | . | 20 42 | . | 1 | . | . | . | . | . |
Carex melanostachya | 9 | 74 42 | 31 | 29 | 15 | 9 | 20 | 20 | 6 |
Linaria biebersteinii | 15 | 47 41 | 3 | 31 23 | . | 2 | . | . | . |
Seseli tortuosum | 10 | 27 38 | . | 4 | . | . | . | . | . |
Eryngium planum | 12 | 35 36 | 3 | 16 | . | . | 3 | 2 | . |
Euphorbia seguieriana | 2 | 16 34 | . | 1 | . | . | . | . | . |
Tragopogon dasyrhynchus | 7 | 19 32 | . | 2 | . | . | . | . | . |
Allium flavum subsp. tauricum | 8 | 18 30 | . | 3 | . | . | . | . | . |
Veronica arvensis | 195 | 9 | 94 79 | 10 | . | . | . | . | . |
Artemisia austriaca | 2 | 8 | 88 76 | 26 13 | . | . | . | . | . |
Cerastium pumilum | 2 | 10 | 75 74 | 8 | . | . | . | . | . |
Carex spicata | . | 1 | 56 72 | . | . | . | . | . | . |
Trifolium retusum | . | 1 | 81 70 | 7 | . | 33 20 | . | . | . |
Poa bulbosa | . | 1 | 66 67 | 20 12 | . | . | . | . | . |
Festuca valesiaca | . | 6 | 56 57 | 21 15 | . | . | . | . | . |
Lepidium draba | 5 | 3 | 50 57 | 10 3 | . | . | . | . | . |
Vicia lathyroides | . | 15 10 | 50 56 | 4 | . | . | . | . | . |
Capsella bursa-pastoris | 6 | . | 41 52 | 7 | . | . | . | . | . |
Taraxacum sect. Taraxacum | 7 | 7 | 62 50 | 218 | 19 | 4 | 1 | 2 | . |
Medicago minima | . | . | 28 47 | . | 4 | . | . | . | . |
Crepis ramosissima | 9 | 17 | 62 45 | 36 20 | 17 | . | 1 | . | . |
Cruciata pedemontana | 178 | 26 19 | 47 43 | . | . | . | . | . | . |
Arenaria leptoclados | . | 3 | 41 38 | 20 13 | 8 | 13 | . | . | . |
Trifolium arvense | 4 | 1 | 25 36 | 9 8 | . | . | . | . | . |
Stellaria graminea | 3 | 14 | 38 32 | 15 6 | 21 13 | . | . | . | . |
Allium regelianum | 1 | 8 | . | 66 59 | 15 | . | 11 | 5 | . |
Herniaria glabra | . | . | . | 45 47 | . | 28 25 | 2 | . | . |
Artemisia santonicum | . | 3 | . | 71 47 | 38 17 | 35 14 | 14 | 5 | 6 |
Plantago lanceolata | . | 2 | 25 20 | 44 44 | . | 2 | 4 | 2 | . |
Ventenata dubia | . | 2 | . | 20 39 | . | . | 1 | . | . |
Lepidium ruderale | . | . | . | 12 33 | . | . | . | . | . |
Potentilla argentea | 1 | 51 21 | 34 | 65 33 | 2 | 7 | 25 | 39 | . |
Polycnemum arvense | . | . | . | 11 32 | . | . | . | . | . |
Cyperus flavescens | . | 3 | . | 8 | 58 48 | . | 36 25 | 7 | . |
Lathyrus nissolia | . | . | 6 | . | 31 48 | . | . | . | . |
Armoracia rusticana | . | . | . | . | 19 37 | . | 4 | . | . |
Crepis sancta | 2 | 1 | . | 2 | 19 36 | . | . | . | . |
Lathyrus tuberosus | . | . | . | 3 | 17 36 | . | . | . | . |
Phalacrachena inuloides | . | 7 | 19 | 16 7 | 38 32 | . | 6 | 10 | . |
Lotus angustissimus | . | 1 | . | 43 23 | 12 | 93 68 | 15 | . | . |
Myosurus minimus | 1 | 15 | 3 | 28 6.0 | . | 98 67 | 28 7 | 10 | 6 |
Mentha pulegium | . | . | . | . | . | 39 57 | 3 | . | . |
Lythrum virgatum | . | 5 | . | 34 5 | 17 | 91 49 | 54 20 | 56 22 | . |
Chaiturus marrubiastrum | . | . | . | 2 | . | 31 43 | 13 12 | . | . |
Polygonum aviculare | . | 20 | 9 | 57 8 | 23 | 100 40 | 45 | 61 12 | 83 28 |
Erigeron canadensis | 2 | . | . | 10 6 | 8 | 31 39 | . | . | . |
Xanthium orientale subsp. riparium | . | . | . | 5 | . | 22 33 | 9 10 | . | . |
Aegilops cylindrica | . | . | . | . | . | 11 32 | . | . | . |
Lythrum borysthenicum | . | . | . | 12 12 | . | . | 31 41 | 2 | . |
Elatine hungarica | . | . | . | 1 | 12 10 | . | 24 31 | 10 | . |
Damasonium alisma | . | 5 | . | 2 | . | . | . | 100 97 | . |
Elatine alsinastrum | . | 5 | . | 11 | . | . | 25 12 | 80 69 | . |
Butomus umbellatus | . | . | . | 28 8 | 37 16 | . | 41 20 | 66 42 | . |
Rumex crispus | 9 | 24 | 9 | 30 | 40 14 | . | 42 15 | 61 30 | . |
Rorippa brachycarpa | 30 | 6 | 31 | 52 15 | 48 12 | 54 16 | 71 29 | . | |
Puccinellia distans | . | . | . | 1 | . | . | . | . | 67 79 |
Rumex ucranicus | . | . | . | 2 | . | . | . | . | 67 79 |
Juncus gerardi | . | 1 | . | . | . | . | . | . | 61 76 |
Juncus bufonius | . | . | . | 9 | . | . | 2 | . | 67 73 |
Plantago major | . | 1 | . | 3 | . | 30 18 | . | . | 78 70 |
Ranunculus sceleratus | . | . | . | . | . | . | 7 | 5 | 61 68 |
Bolboschoenus maritimus | . | . | . | 1 | . | . | . | . | 50 68 |
Veronica anagallis-aquatica | . | . | . | . | . | . | . | . | 44 65 |
Petrosimonia triandra | . | . | . | . | . | . | . | . | 39 60 |
Echinochloa crus-galli | . | . | . | 1 | . | . | . | . | 39 59 |
Atriplex prostrata | . | . | . | . | . | . | . | . | 33 56 |
Crypsis schoenoides | . | . | . | 1 | . | . | . | 5 | 39 55 |
Taraxacum besarabicum | . | 2 | . | . | . | . | . | . | 33 53 |
Setaria pumila | . | . | . | 2 | . | 2 | . | . | 22 41 |
Persicaria maculosa | . | . | . | . | . | 4 | 9 8 | . | 28 39 |
Juncus compressus | . | . | . | 1 | . | . | . | . | 17 38 |
Xanthium spinosum | . | . | . | 2 | . | . | . | . | 17 36 |
Plantago tenuiflora | . | 2 | . | 12 2 | 2 | . | 15 5 | 22 14 | 39 33 |
Falcaria vulgaris | 81 61 | 51 33 | . | 14 | . | 4 | . | . | . |
Galium ruthenicum | 79 55 | 66 44 | 6 | 13 | . | . | . | . | . |
Carex praecox | 83 47 | 95 58 | . | 29 | 13 | . | 1 | 2 | . |
Poa angustifolia | 87 32 | 90 34 | 75 23 | 59 | 2 | 2 | 15 | 56 | . |
Alopecurus pratensis | 8 | 42 8 | 100 52 | 27 | . | 6 | 18 | 71 29 | 17 |
Achillea micranthoides | . | 3 | 47 42 | 39 33 | . | 4 | 1 | . | . |
Gypsophila muralis | . | 10 | . | 69 38 | 10 | 100 64 | 22 | . | . |
Inula britannica | 1 | 27 | . | 56 16 | 81 34 | 87 39 | 24 | 29 | 6 |
Eleocharis palustris | . | . | . | 25 | 35 | 100 44 | 53 10 | 46 5 | 94 40 |
Gratiola officinalis | . | 17 | . | 41 6 | 10 | 80 36 | 63 23 | 83 38 | . |
Beckmannia eruciformis | . | 8 | . | 2 | 6 | 76 35 | 31 | 61 23 | 94 49 |
Juncus atratus | . | 6 | . | 3 | . | . | 37 32 | 44 40 | . |
Pulicaria vulgaris | . | 2 | . | 16 3 | . | 31 19 | 13 | 17 | 39 27 |
Phytocenoses of the association Herniario glabrae-Poetum angustifoliae. Small Chapelsky Pid, peripheral part of the bottom, public pasture of cattle (near the village of Dolynsky), communities dominated by Poa angustifolia with Artemisia santonica, Allium regelianum, Achillea micranthoides, Diantus guttatus, Plantago lanceolata, 26.06.2010.
Phytocenoses of the subassociation Elatino-Butometum umbellati damasonietosum alismae in the central part of the bottom of the Great Chapelsky pid during flooding, flowering individuals of Damasonium alisma among vegetative shoots of Butomus umbellatus and Elytrigia repens subsp. pseudocaesia, 17.05.2010.
DCA-ordination of the resulted vegetation units. Numbers in the centroids correspond to the unit number in the text. Environmental verctors of DES: Hd – moisture, fH – variability of damping, Rc – soil acidity, Sl – salt regime of a soil, Ca – carbonate content in a soil, Nt – nitrogen content in a soil, Ae – soil aeration, Tm – thermal regime, Om – humidity of climate (ombroregime), Kn – continentality of climate, Cr – cryoregime, Lc – light. Eigenvalues: 1st axis (DCA1) 0.6533, 2nd axis (DCA2) 0.2723.
Ecological and coenotic profile of model steppe depressions of the Left Bank of the Lower Dnieper. The central part of the bottom is occupied by wetland communities, which change along the slopes by wet, mesic and xero-mesic phytocenoses. The transectshows the difference in absolute height between the bottom of the depression and its slope, the length and asymmetry of the «body» of the depression along the line: slopebottom. Species: 1 – Stipa ucrainica, 2 – Koeleria macrantha, 3 – Agropyron cristatum subsp. pectinatum, 4 – Galatella villosa, 5 – Achillea micranthoides, 6 – Atriplex oblongifolia, 7 – Artemisia austriaca, 8 – Carex praecox, 9 – Poa angustifolia, 10 – Carex melanostachya, 11 – Phlomis scythica, 12 – Allium regelianum, 13 – Festuca valesiaca, 14 – Artemisia santonicum, 15 – Alopecurus pratensis, 16 – Chaiturus marrubiastrum, 17 – Inula britannica, 18 – Rorippa brachycarpa, 19 – Elytrigia repens subsp. pseudocaesia, 20 – Lotus angustissimus, 21 – Phalacrachena inuloides, 22 – Beckmannia eruciformis, 23– Lythrum virgatum, 24 – Mentha pulegium, 25 – Puccinellia distans, 26 – Gratiola officinalis, 27 – Juncus atratus, 28 – Rumex ucranicus, 29 – Damasonium alisma, 30 – Eleocharis palustris, 31 – Butomus umbellatus, 32 – Pulicaria vulgaris, 33 – Ferula euxina, 34 – Sibbaldianthe bifurca subsp. orientalis, 35 – Bassia prostrata, 36 – Salvia nemorosa subsp. tesquicola, 37 – Tanacetum millefolium, 38 – Polygonum patulum, 39 – Ventenata dubia, 40 – Elatine alsinastrum, 41 – Myosurus minimus, 42 – Schoenoplectus lacustris. For the two-letter abbreviations of environmental factors – see Figure
Distribution of rare and endangered vascular plant taxa in nine units of pody vegetation (the cluster numbers correspond to their numbers in the text, see Section 4.1). Status of red-listed species: RBU – Red Data Book of Ukraine (
Taxon | Status (category) | Total | Clusters | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |||
Achillea micranthoides | RLKhO | 10.6 | 3.5 | 46.9 | 38.5 | 3.7 | 1.1 | ||||
Alisma gramineum | IUCN RL (dd) | 0.3 | 4.7 | ||||||||
Allium regelianum | RBU (r), Bern, Eu RL (dd) | 16.8 | 0.7 | 8.2 | 65.6 | 15.4 | 10.5 | 4.7 | |||
Beckmannia eruciformis | Eu RL (dd) | 19.3 | 4.7 | 1.6 | 5.8 | 75.9 | 30.5 | 65.1 | 94.4 | ||
Bellevalia speciosa | RLKhO | 0.2 | 0.7 | ||||||||
Damasonium alisma | RBU (en), Eu RL (nt) | 7.2 | 2.4 | 1.6 | 97.7 | ||||||
Elatine alsinastrum | Eu RL (nt) | 11.7 | 2.4 | 11.5 | 25.3 | 81.4 | |||||
Elatine hungarica | RBU (vu), RLKhO, Eu RL (dd) | 5.1 | 0.8 | 11.5 | 24.2 | 7.0 | |||||
Elytrigia repens subsp. pseudocaesia | RLKhO | 52.9 | 10.7 | 96.5 | 28.1 | 57.4 | 92.3 | 79.6 | 38.9 | 62.8 | 44.4 |
Ferula caspica | RLKhO | 0.3 | 0.7 | 1.2 | |||||||
Juncus sphaerocarpus | RBU (en) | 2.2 | 5.7 | 7.4 | |||||||
Lathyrus nissolia | RLKhO | 2.8 | 6.3 | 30.8 | |||||||
Lythrum thymifolia | RBU (vu) | 7.3 | 20.5 | 22.1 | 2.3 | ||||||
Peucedanum ruthenicum | RLKhO | 3.3 | 12.1 | 4.7 | |||||||
Phalacrachena inuloides | RLKhO | 9.7 | 7.1 | 18.8 | 16.4 | 38.5 | 6.3 | 9.3 | |||
Phlomis scythica | RBU (ne) | 13.1 | 16.4 | 8.2 | 9.4 | 19.7 | 13.7 | 32.6 | |||
Pholiurus pannonicus | RLKhO | 6.1 | 9.8 | 3.8 | 21.1 | 27.8 | |||||
Prunus tenella | RLKhO | 0.2 | 0.7 | ||||||||
Stipa capillata | RBU (ne) | 1.7 | 7.1 | 1.2 | |||||||
Stipa ucrainica | RBU (ne) | 0.2 | 1.2 | ||||||||
Tulipa scythica) | RBU (en) | 0.6 | 3.3 | ||||||||
Total number of red listed taxa per vegetation unit | 21 | 8 | 12 | 5 | 13 | 7 | 3 | 11 | 10 | 3 |
The DCA ordination of the identified units (Figure
Peculiarities of ecological differentiation of steppe depression syntaxa can be traced on the transect across the conditional (model) depression, which has well-preserved natural slopes and bottom and is periodically flooded (Figure
The classification of vegetation plots by the expert system EVC (Suppl. material
The interpretation of vegetation plots by the expert system EUNIS-ESy in units of the EUNIS habitat classification (Suppl. material
The obtained results of the vegetation classification, in particular the list of diagnostic, constant and dominant species of the syntaxa (Suppl. material
Units 3–5 obviously represent mesic grasslands and their mesophytic character was shown by the results of phytoindication. According to the results of the analysis using the EVC expert system, a significant number of plots are assigned to the class Molinio-Arrhenatheretea, which is also confirmed by the results of the analysis using the expert system EUNIS-ESy, which assigned these plots to mesic grassland habitats. Therefore, we classify them within the Molinio-Arrhenatheretea class. Among the higher-ranking syntaxa recognized in EuroVegCheklist, these communities are the most similar to the order Althaeetalia officinalis and its alliance Althaeion officinalis. Although the diagnosis of the order and alliance in the original publication (
The wettest associations of depression bottoms (clusters 6–8) showed some inconsistency in their interpretation by expert systems – on the one hand, the EVC expert system assigned most of their plots to the Molinio-Arrhenatheretea class, and on the other hand the EUNIS-ESy expert system interpreted most of their plots as C (Surface waters) and Qb (Wetlands) groups. But this inconsistency is quite understandable given the ephemeral and complex nature of these habitats and irregularity of flooding. In view of this, we propose that the nature of these communities best fits the class Isoёto-Nanojuncetea, defined as “Pioneer ephemeral dwarf-cyperaceous vegetation in periodically freshwater flooded habitats of Eurasia” in
Cluster 9, according to the list of diagnostic species and the analysis using expert systems, can be assigned to the class Festuco-Puccinellietea. This is the only community that has a pronounced halophytic character, which distinguishes it from all other analyzed units. This difference, both floristic and ecological, might explain the erroneous attribution of the steppe depression vegetation in general to the halophytic type. This unit should probably be attributed to the order Scorzonero-Juncetalia gerardi. However, the transitional nature of the communities as well as the source of the chloride salinity does not currently allow them to be attributed to any of the existing alliances.
The obtained results once again showed that the vegetation of steppe depressions (pody) is indeed rather complex, but not «mosaic», because it was not possible to isolate phytocenoses of annual (ephemeral) plants characteristic for the class Isoёto-Nanojuncetea, and separate them spatially or in time from grassland or wetland communities of perennial plants. Even in the plots of small size in small depressions and bottom depressions with the longest duration of flooding, both ephemeral annual and perennial species were present. Of course, the increase in the plot size slightly changed the proportions of individual and total cover, but in no way affected the homogeneity and integrity of the studied plant communities. It can be assumed that with sufficiently long floods and increasing depth of a water body, some mesophytic or xeromesophytic plants, which are common in dry, non-flooded depressions, would disappear from the communities. Then we would probably get localized occurrences of ephemeral annual vegetation, confined to drying puddles. But irregular and short-term flooding of depressions (every 7–10 yrs, sometimes 20 yrs, lasting only 2–3 months), as well as the shallowness of temporary standing water (about 30–40 cm deep at the peak of the flood and then becoming shallow, 5–10cm) do not adversely affect perennial mesophytic species. It is worth noting that the closed bottoms of the depressions in the natural intact state is a perfectly flat surface, so the edaphic conditions, moisture regime and other abiotic parameters are almost identical throughout a flooded bottom. Thus, when the depressions are flooded and then begin to dry in the same season, peculiar combinations of ephemeral annual aquatic plants and perennial grassland and wetland plants are observed. These plants grow in different layers, but within the same phytocenosis. Such an original complex of hydrophytic vegetation (“ephemeretum”) is indivisible either territorially or chronologically.
When interpreting the obtained units, we tried to compare them with the units described in the very first work on the pody vegetation (
Our testing of two expert systems showed that they can be used as an additional tool for interpreting the results of vegetation classification, especially for assigning associations to syntaxa of a higher hierarchical rank. However, for such complex communities, and, accordingly, complex habitat types, the use of expert systems has limitations, since their nature is such that communities can contain species of different ecological groups, different vegetation classes, and, accordingly, different discriminant or functional species groups, which often overlap. These features prevent the correct interpretation of the relevés by an expert system.
Taking into account that all previously described units of the steppe depression vegetation are invalid, because the nomenclature type was not indicated using expressis verbis the Latin words ‘typus’ or ‘holotypus’(ICPN Art. 5, par.3), we validly describe the syntaxa of the steppe depression vegetation which we accepted, according to the analysis presented in this paper. When validating the previously described syntaxa, we have kept all their nomenclature types, which are also presented in this article in the Suppl. material
Our analysis allowed us to propose an updated syntaxonomic system of mesic and wet grassland vegetation of the steppe depressions, which reflects their ecological and territorial differentiation, to restore a syntaxonomic status of a number of syntaxa that were considered doubtful, and to find a proper place of the steppe depression vegetation in the syntaxonomic system of the European vegetation (
The data used in the paper are available as Supplementary material in *.xlsx format and in *.csv format.
V.S. formulated the idea of the paper, prepared the dataset for the analysis (85% of the relevés are his own), reviewed the literature, wrote a description of the obtained vegetation units and interpreted them at the level of associations, subassociations and alliances. A.K. planned the research, made all analyzes and interpreted the obtained units at the level of orders and classes. The authors jointly prepared the manuscript.
The authors are grateful to Orysia Goffman for the data provided, to Ivan Moisiyenko for his help with field study in 2019 and information provided about previously unknown depression in the “Harbuzy” site, to Dariia Shyriaeva for the preparation of the map in Figure