ACTA BOT. CROAT. 78 (2), 2019 155 Acta Bot. Croat. 78 (2), 155–163, 2019 CODEN: ABCRA 25 DOI: 10.2478/botcro-2019-0013 ISSN 0365-0588 eISSN 1847-8476 Phytosociology and biodiversity patterns of annual wetland communities of Pyriatynskyi National Nature Park (Poltava Oblast, Ukraine) Oleksii Kovalenko*, Mariia Kalista Department of Botany, National Museum of Natural History of NAS of Ukraine, Bohdana Khmelnytskoho 15, 01607 Кyiv, Ukraine Abstract – The results of a comparative structural analysis of the annual wetland herb vegetation syntaxa (class Isoëto-Nano-Juncetea) of Pyriatynskyi National Nature Park (Poltava Oblast, Ukraine) are presented. The system- atic, biomorphological, ecological and geographical structures of syntaxa were studied using cluster, discriminant and factor analysis. The principal conformity of the floristic similarity dendrogram and the previously developed classification scheme were analysed. It was revealed that the leading factor of coenosis development is the soil moisture, while most parameters of these ecotopes are constant. The critical differentiation of Nano-Cyperion and Eleocharition ovatae alliances and the legitimacy of the recognition of the Radiolion linoidis alliance and Polygono recti-Juncetum juzepczukii association as separate syntaxa of the main ranks are emphasized. Keywords: analysis of syntaxa, annual wetland, herb vegetation, Isoëto-Nano-Juncetea vegetation, syntaxonomy * Corresponding author e-mail: corydalis@ukr.net, crambe@ukr.net Introduction One of the problems of modern phytosociology is the harmonization of regional systems of classification and monographic processing of some classes of vegetation. This fully applies to dynamic and compositionally complex com- munities of the annual wetland herb vegetation belonging to the class Isoëto-Nano-Juncetea Br.-Bl. et Tx. ex Br.-Bl. et al. 1952. Despite more than a century of research in Western and Central Europe (Ellenberg 1982), as well as recent in- tensive research in Siberia and Eastern Europe (Taran 1993, 1995, 2001, Senchylo and Goncharenko 2008a, b, Shapoval 2006, Golub et al. 2007, Kovalenko 2014), there is consid- erable confusion in the definition and interpretation of the main associations and alliances of this class. To build a sta- ble hierarchical system of Isoëto-Nano-Juncetea, we propose to use a complex comparative and structural analysis of de- termined syntaxa as multiparameter systems (Senchylo and Goncharenko 2008a). Materials and methods We studied the annual wetland herb vegetation of the Pyriatynskyi National Nature Park (NNP) (Poltava Oblast, Ukraine) in 2010–2012. We have already proposed its syn- taxonomical scheme and described 2 associations as new for science (Kovalenko 2014). The floristic similarity of the syntaxa determined was counted using the Index of inclusion of Kulchytsky (Sem- kin and Komarova 1977). Peculiarities of ecological differ- entiation of communities of the annual wetland herb veg- etation were assessed by the method of synphytoindication (Didukh and Pliuta 1994), using the ecological scales of Didukh (2011). The comparative and structural analysis of the syntaxa was carried out according to 5 groups of param- eters: taxonomical, biomorphological (the main type of bio- morph, the character of seasonal vegetation, the structure of the above-ground and underground shoots, the type of the root system, the type of pubescence, the methods of polli- nation and dissemination), the chorological (type of range, chorionic element and activity), ecological and coenotical (tolerance for climatic and edaphic factors, ecological strat- egy) block and the block of transformation of flora (toler- ance for anthropogenic factors, resistance to conditions of urbanization and hemeroby). The basic principles of the al- location of these categories are justified in the works of No- vosad and Krytska (2010) and also Senchylo and Goncha- renko (2008a). KOVALENKO O., KALISTA M. 156 ACTA BOT. CROAT. 78 (2), 2019 In our analysis we used the parameter “purity of syn- taxon”, which means the percentage ratio of the diagnostic species to the general list of flora. It indicates a role of the ephemeral annuals in the composition of communities that are critically important for the determination of the syntaxa of the Isoëto-Nano-Juncetea class. For factor analysis, we used 121 non-discrete parameters of the systematic, biomorphological, ecological-coenotical and geographical structures. This data set includes floristic information and results of ordination by the phytoindica- tion method. The data obtained were used for cluster, canonical dis- criminant and factor analysis in the Statistica 7.0 program (StatSoft). Results Annual wetland communities of Pyriatynskyi National Nature Park are presented by 1 order, 4 alliances and 7 as- sociations: Cl. Isoëto-Nano-Juncetea Br.-Bl. et Tx. ex Br.-Bl. et al. 1952 Ord. Nano-Cyperetalia Klika 1935 All. 1. Nano-Cyperion flavescentis Koch ex Libbert 1932 Ass. 1. Cyperetum flavescentis Koch ex Aichinger 1933 2. Juncetum bufonii Felföldy 1942 All. 2. Eleocharition ovatae Philippi 1968 Ass. 3. Cyperetum micheliani Horvatić 1931 4. Eleocharito acicularis–Limoselletum aquati- cae Wendelberger-Zelinka 1952 All. 3. Radiolion linoidis Pietsch 1973 Ass. 5. Psammophiliello–Juncetum nastanthi Kova- lenko 2014 All. 4. Verbenion supinae Slavnič 1951 Ass. 6. Polygono recti–Juncetum juzepczukii Kova- lenko 2014 7. Eragrostidetum suaveolentis Golub et al. 2007 The analysis of the floristic similarity of syntaxa (On- line Suppl. Tab. 1) with subsequent clustering is followed by dendrogram (Fig. 1). The branching of trees did not change significantly depending on the chosen binding parameters. The first clade was formed by associations of Verbenion supinae and Radiolion linoidis alliances. The associations of Verbenion supinae are the most similar to each other by flo- ristic criteria. Psammophiliello–Juncetum nastanthi associa- tion is well-separated from this alliance. The second cluster of the dendrogram was formed by associations belonging to two alliances (Nano-Cyperion flavescentis and Eleochari- tion ovatae). The basic coeofloristic proportions are the parameter that shows the systematic richness of the syntaxa (number of genera and species per one family). This parameter is similar for the determined syntaxa of Isoëto-Nano-Juncetea (Tab. 1). Tab. 1. Coenofloristic proportions of the syntaxa of the Isoëto-Nano-Juncetea of Pyriatynskyi National Nature Park.The basic proportions are parameters that indicate an average number of species in families and average number of genera in families in floristic composition. Generic coefficient is an average number of species in all genera. Magnoliopsida to Liliopsida ratio is a ratio of monocots to dicots. Spe- cies richness of coenoses is a parameter that indicates a number of species in one relevé with average standard deviation as numbers. The “Purity of syntaxon” is a ratio of diagnostic species within the floral composition (first number indicates absolute number of community diagnostic species; the second number indicates a percentage contribution). Syntaxon Basic proportions Generic coefficient Magnoliopsida to Liliopsida ratio Species richness coenoses «Purity syntaxon» (%) Cyperetum flavescentis 1 : 1.47 : 1.73 1.18 2 11.08±3 10; 38.46 Juncetum bufonii 1 : 1.27 : 1.64 1.29 2.6 6.64±3 13; 72.22 Cyperetum micheliani 1 : 1.38 : 1.75 1.27 3.67 10.64±7.81 21; 75 Eleocharito-Limoselletum 1 : 1.76 : 2.44 1.39 2.42 7.55±5.45 16; 26.23 Psammophiliello-Juncetum 1 : 1.08 : 1.33 1.23 2.2 9.26±3.74 12; 75 Polygono-Juncetum 1 : 2.4 : 3.2 1.33 3.2 9±5 13; 40.63 Eragrostidetum suaveolentis 1 : 1.62 : 1.77 1.10 3 8.46±2.54 17; 73.91 Nano-Cyperion 1 : 1.39 : 1.94 1.4 1.5 8.96±4.04 17; 48.57 Eleocharitionovatae 1 : 1.71 : 2.54 1.48 2.63 7.88±7.62 23; 32.39 Radiolion linoidis 1 : 1.08 : 1.33 1.23 2.2 9.26±3.74 12; 75 Verbenion supinae 1 : 2.38 : 2.93 1.33 2.73 9.12±3.78 18; 43.9 Nano-Cyperetalia and Isoëto-Nano-Juncetea 1 : 2.41 : 3.89 1.62 1.94 8.74±8.63 41; 39.05 Fig. 1. Dendrogram of the floristic similarity of associations of the annual wetland herb vegetation of Pyriatynskyi NNP: 1 – Cyper- etum flavescentis; 2 – Juncetum bufonii; 3 – Cyperetum micheliani; 4 – Eleocharito acicularis–Limoselletum aquaticae; 5 – Psammophi- liello–Juncetum nastanthi; 6 – Polygono recti–Juncetum juzepczukii; 7 – Eragrostidetum suaveolentis. ANNUAL WETLAND COMMUNITIES OF PYRIATYNSKYI NATIONAL PARK ACTA BOT. CROAT. 78 (2), 2019 157 The percentage ratio of diagnostic species to the gen- eral list of flora (“purity of syntaxon”) negatively correlates with the duration of vegetation of communities, reaching the minimum values for the most trivial association of Ele- ocharito-Limoselletum (On-line Suppl. Fig. 1). The genus Juncus dominates in the annual wetland herb vegetation of Pyriatynskyi NNP (6 species, 5.7%). This also corresponds to the phytocoenotic role of its representatives in characteristic coenoses. The Carex genus in the commu- nities studied is represented by 5 species (4.77%), but with no typical ephemerals among them. The third position is oc- cupied by the temperate-tropical Persicaria genus (4, 3.81%), whose representatives are particularly active in the coenoses of the Eleocharition ovatae alliance. Also, four species in the phytocoenoses of the annual wetland herb vegetation belong to the Polygonum genus, which has the highest constancy in the Verbenion supinae alliance. Among the morphological traits (Tab. 2) of the floris- tic composition of the class Isoëto-Nano-Juncetea, monoe- cious plants (including facultative ones) take the first place, slightly ahead of the relative number of herbaceous perennial plants. An almost equal ratio of these two life forms is char- acteristic for the communities Cyperetum flavescentis and Eleocharito-Limoselletum, and also in general for the unions of Nano-Cyperion and Eleocharion ovatae, while the remain- ing syntaxa have a considerable dominance of annuals. Pe- rennial plants, as a rule, do not undergo a full cycle of de- velopment and are represented mainly by pregenerative age states in communities of the annual wetland herb vegetation. According to the type of above-ground shoots, the main group is composed of erosulate plants; only in the associa- tion Cyperetum flavescentis do semirosette forms have the main position. A distinctive feature of the communities Isoë- to-Nano-Juncetea is the high share of species with an ephem- eral type of vegetation. With decreasing humidity of specific habitats, the relative participation of summer-green plants increases, reaching the maximum values in the communi- ties of the Verbenion supinae. The plants with fibrous root systems are more common in mesohygrophytic conditions, whereas with increasing xerophyticity the specific gravity of the tap root species increases. In the type of underground shoots, plants without rhizomes predominate, although the involvement of the short rhizome species is noticeable in the composition of the vegetative cover of hygrophytic and mesophytic alliances of Nano-Cyperion, Eleocharion ovatae and Radiolion linoidis. Most annual wetland herbs are insect-pollinated or wind-pollinated plants (Fig. 2a), however, self-pollination has a significant part in the phytocoenosis of the class. The specific gravity of the latter increases in the most extreme habitats typical of the associations Juncetum bufonii and Psammophiliello-Juncetum. The leading ways of diasporas dispersal are anemochory, barochory, zoochory (mainly epizoochory) and hydrochory (Fig. 2b). The ratio of representatives of these dissemination strategies does not change significantly in each individual syntaxon. Seasonal fluctuations of moisture conditions from hy- grophilic to xeromesophilic are reflected in the distribu- tion of species according to the degree of pubescence (Fig. 2c). In all coenoses, the group of non-pubescent plants is dominant, and in communities with the shortest period of flooding (Radiolion linoidis and Verbenion supinae), the pro- portion of heavily pubescent species is increased, while the prolonged phase of moistening promotes the groups of me- dium-inferior species. Tab. 2. Morphological traits structure of the annual wetland herb vegetation syntaxa of Pyriatynskyi National Nature Park. Syntaxon Life form %) Aboveground shoots (%) Root system (%) Phenological groups (%) Underground shoots (%) A nn ua ls Pe re nn ia ls Tr ee s R os et te Se m ir os et te Eo su la te te Ta pr oo t Fi br ou se Ep he m er al s Su m m er -g re en Su m m er -w in te r- gr ee n W ith ou t r hi zo m e Lo ng -r hi zo m e Sh or t r hi zo m e C au de x Cyperetum flavescentis 50.0 50.0 0.0 11.5 53.9 34.6 38.5 61.5 62.3 29.2 38.5 50.0 19.2 23.1 7.7 Juncetum bufonii 77.8 22.2 0.0 16.7 38.9 44.4 66.7 33.3 66.7 22.2 11.1 72.2 0.0 22.2 5.6 Cyperetum micheliani 78.6 21.4 0.0 7.1 32.1 60.8 60.7 39.3 71.4 21.4 7.1 78.5 3.6 14.3 3.6 Eleocharito-Limoselletum 55.7 42.7 1.6 9.8 39.4 50.8 50.0 50.0 31.1 42.7 26.2 47.6 18.0 24.6 9.8 Psammophiliello-Juncetum 75.0 25.0 0.0 18.8 25.0 56.2 50.0 50.0 43.8 37.5 18.7 75.0 0.0 25.0 0.0 Polygono-Juncetum 71.8 21.9 6.3 0.0 58.5 41.5 53.1 46.9 40.6 501 9.3 78.1 3.1 9.4 9.4 Eragrostidetum suaveolentis 87.0 8.7 4.3 0.0 43.5 56.5 60.9 39.1 56.5 34.8 8.7 91.4 4.3 4.4 0.0 Nano-Cyperion 54.3 45.7 0.0 11.4 48.6 40.0 48.6 51.4 42.9 25.7 31.4 54.2 14.3 22.9 8.6 Eleocharition ovatae 51.4 47.1 1.5 58.6 35.7 45.7 50.0 50.0 30.0 45.7 24.3 52.8 15.7 22.9 8.6 Radiolion linoidis 75.0 25.0 0.0 18.8 25.0 56.2 50.0 50.0 43.7 37.5 18.8 75.0 0.0 25.0 0.0 Verbenion supinae 77.8 17.8 4.4 0.0 44.5 55.5 66.7 33.3 37.8 48.9 13.3 82.2 4.4 6.7 6.7 Nano-Cyperetalia and Isoëto-Nano-Juncetea 55.8 42.3 1.9 6.7 48.2 45.1 51.0 49.0 29.8 26.0 44.2 58.7 14.4 20.2 6.7 KOVALENKO O., KALISTA M. 158 ACTA BOT. CROAT. 78 (2), 2019 Soil humidity has the leading value among factors char- acterizing edaphic conditions (Didukh 2011). According to it, the highest range of amplitude has Eleocharito acicularis– Limoselletum aquaticae. Communities of these associations are common for the national park and forms in habitats with different regimes of humidity. Associations Cyperetum fla- vescentis, Juncetum bufonii and Cyperetum micheliani have similar values of these factors. The vegetation of the allianc- es Radiolion linoides and Verbenion supinae are presented on the most xeric soils. The communities of Eragostidetum suaveolentis are clearly different from Polygono-Juncetum ac- cording to their humidity regime (Fig. 3a). The variability of moisture is very important factor for annual wetland communities. All associations excluding Eragostidetum suaveolentis and Polygono-Juncetum have a similar range of values. Dry soils in the habitats of Verbe- nion supinae are the main reason for the invasion of species with adaptation to hydrocontrastophily (irregular wetting of soil layer) in characteristic communities (Fig. 3b). According to the relations of associations to soil acidity and total salt regime we can clearly see the differentiation of Cyperetum flavescentis due to existing soils with sodium sulphate salting (Figs. 3c, d). This association has a higher rank of carbonate content in the soil too (Fig. 3e). Also, Ra- diolion linoides communities grow on chernozems, enriched enough with carbonates. Almost all associations have similar ranks of nitrogen content in soil. The most nitrophilic syntaxa are Cyperetum flavescentis and Eleocharito acicularis–Limoselletum aquati- cae. On the other hand, communities of Eragostidetum sua- veolentis include a lot of plants that grow on poor mineral- nitrogen oligotrophic soils (Fig. 3f ). Soil aeration limits the distribution of many ephemer- al annual herbs. The highest ranking (9.37) is Eleocharito acicularis–Limoselletum aquaticae, the lowest rank (6.44) is characteristic for Eragostidetum suaveolentis. Other syn- taxa are very similar (Fig. 4a) according to this parameter (7.33–8.67). According to the thermal climate and humidity, all of the associations demonstrated no significant value of varia- tion (Figs. 4b, c). Other climate parameters are the source of differentiation of Isoëto-Nano-Juncetea syntaxa. In Juncetum bufonii and associations of Radiolion and Verbenion subcon- tinental species prevail. In the other syntaxa, we determined the dominance of hemi-oceanic elements (Fig. 4d). By the parameter of the cryo-climate, we identified Cy- peretum flavescentis as the most cryophilic association due its northern area of distribution (Fig. 4e). The regimes of light in characteristic habitats of the an- nual wetland vegetation are similar. Most syntaxa have strict ranges of amplitude by this parameter. Only communities of Polygono-Juncetum have lower value of light due their devel- opment in partly woody areas (Fig. 4f ). The canonical discriminant analysis showed a clear dis- persion of the Cyperetum flavescentis, Cyperetum micheliani, Eleocharito-Limoselletum and Eragrostidetum associations (Fig. 5). The remaining associations from three different al- liances demonstrated a significant overlap in the amplitudes of the whole set of ecological parameters studied, as already mentioned above. The chorological core of the class in the national park is wide-ranging progressive species with Holarctic (22; 31.73%), cosmopolitan (22, 21.15%) and Palaearctic (12, 11.53%) types of areas. The proportion of geographic elements has a simi- larity in all syntaxa, with the exception of the Verebenion. In this alliance, cosmopolitan species dominate. Anthropogenic transformation of communities of the annual wetland vegetation ephemeretum is manifested in the significant representation in the general list of flo- ra of euhemerobes (27; 25.96%) and mesohemerobes (40; 38.46%). Euhemerobes are particularly active in the coe- noses of the association Eragrostidetum suaveolentis, but in more humid conditions they are rare. Fig. 2. The types of pollination (a), dissemination (b) and pubes- cence (c) of syntaxa Isoëto-Nano-Juncetea plants. 1 – Cyperetum flavescentis; 2 – Juncetum bufonii; 3 – Cyperetum micheliani; 4 – Eleocharito acicularis–Limoselletum aquaticae; 5 – Psammophili- ello–Juncetum nastanthi; 6 – Polygono recti–Juncetum juzepczukii; 7 – Eragrostidetum suaveolentis; All.1 – Nano-Cyperion; All.2 – Eleocharition ovatae; All.3. – Verbenion supinae. Contribution of different species (%) are presented. ANNUAL WETLAND COMMUNITIES OF PYRIATYNSKYI NATIONAL PARK ACTA BOT. CROAT. 78 (2), 2019 159 The ratio of urbanophiles, urbanoneutral and urban- ophobic species is correlated with the previous indicator. Among the apophytes, the prevalent hemiapophytes (29; 54.71%), euapophytes and random apophytes in all syntaxa are represented uniformly. The lowest percentage of alien species was noted for the alliances of Nano-Cyperion and Radiolion lionoidis (5.50% and 6.25% respectively), while similar indicators for the al- liances Eleocharition ovatae (12.86%) and Verbenion supinae (21.95%) are significantly higher. The absolute majority of alien species are coenophytes (10, 66.67%) predominantly of North American origin (8, 53.33%). The factor analysis by the principal components meth- od (Fig. 6) showed, on one hand, a significant affinity for the associations Cyperetum micheliani and Juncetum bufo- nii, which are discrete in floral, physiognomic and ecologi- Fig. 3. Box-whisker plot for distribution of associations of the class Isoëto-Nano-Juncetea by: a) soil humidity (Hd); b) moisture (fH); c) acidity (Rc); d) total salt regime (Sl); e) carbonate content in soil (Ca); f ) nitrogen content in soil (Nt). 1 – Cyperetum flavescentis; 2 – Juncetum bufonii; 3 – Cyperetum micheliani; 4 – Eleocharito acicularis–Limoselletum aquaticae; 5 – Psammophiliello–Juncetum nastanthi; 6 – Polygono recti–Juncetum juzepczukii; 7 -Eragrostidetum suaveolentis. Box-whisker plot: centre line denotes median value, the box encloses the inner two quartiles (25th and 75th percentile), and the whiskers display the 10th and 90th percentile. KOVALENKO O., KALISTA M. 160 ACTA BOT. CROAT. 78 (2), 2019 cal relationships while on the other hand it clearly delineated the associations of the Verbenion supinae association, which were close by the same criteria. Discussion Results of cluster analysis of syntaxa correspond strongly to the obtained scheme of classification. However, the asso- ciation Juncetum bufonii did not unite with the Cyperetum flavescentis, as might be expected according to the syntaxo- Fig. 4. Box-whisker plot for distribution of associations of the class Isoëto-Nano-Juncetea by: a) aeration (Ae); b) thermal climate (Tm); c) humidity (Om); d) continental climate (Kn); e) cryoclimate (Cr); f ) light in community (Lc). 1 – Cyperetum flavescentis; 2 – Juncetum bufonii; 3 – Cyperetum micheliani; 4 – Eleocharito acicularis–Limoselletum aquaticae; 5 – Psammophiliello–Juncetum nastanthi; 6 – Polygono recti–Juncetum juzepczukii; 7 – Eragrostidetum suaveolentis. Box-whisker plot: centre line denotes median value, the box encloses the inner two quartiles (25th and 75th percentile), and the whiskers display the 10th and 90th percentile. nomic position. Juncetum bufonii has a high level of floris- tic similarity with associations of the Eleocharition ovatae alliance. On one hand, this result confirms the need for the recognition of the separate alliance Juncion bufonii Philippi 1968 or, by contrast, a wider understanding of the Nano-Cy- perion alliance, as suggested by a number of authors (Borhidi 2003, Sanda et al. 2008), but without inclusion in its commu- nities of Radiolion linoidis. In our opinion, this discrepancy between the dendrogram and the proposed syntaxonomic scheme is due to the regional difference of Juncetum bufonii ANNUAL WETLAND COMMUNITIES OF PYRIATYNSKYI NATIONAL PARK ACTA BOT. CROAT. 78 (2), 2019 161 communities with their main distribution area in the north, as well as their spatio-functional contacts with the phytocoe- noses of the Eleocharion ovatae alliance. Coenofloristic pro- portion diagnoses a rather low overall level of species diver- sity, which is due to the unique ecological parameters of the characteristic communities of the class. Due to the increase of the moisture gradient, the coenotic role and represen- tation of monocots in the communities also increase. The spectrum of the leading families of the annual wetland herb vegetation differs significantly from analogous relationships for other types of vegetation. In addition, if the dominance of the representatives of Asteraceae and Poaceae is the back- ground for most of the coenofloras of the Holarctic temper- ate zone, and the increasing role of Cyperaceae is typical for communities of Phragmiti-Magno-Caricetea and Scheuchze- rio-Caricetea nigrae classes, then the high positions of Po- lygonaceae and Juncaceae are a distinctive feature for Isoëto- Nano-Juncetea. The ecological analysis of Isoëto-Nano-Juncetea vegeta- tion showed the clearest differentiation of associations ac- cording to the soil moisture factor. The Nano-Cyperion al- liance is traditionally considered the most hygrophytic. However, we find communities of Cyperetum micheliani and Eleocharito-Limoselletum associations in conditions with higher soil moisture. The answer to whether this is a regional specificity, or yet more evidence in favour of an ex- panded understanding of the Nano-Cyperion will be given by detailed comparative studies of the ecological amplitude of the union throughout the range. According to substrate chemistry, most associations did not show significant differ- ences. In the general background, only the Cyperetum fla- vescentis association, genetically linked to weakly saline eco- topes, stands out. Concerning the factors of thermo-regime and continentality, the association Eragrostidetum suaveo- lentis, described from the Volga-Akatubinsk annual wetland herb vegetation, is clearly differentiated, and found its west- ern boundary of distribution here. The coenotic differentiation of the syntaxa of annual wet- land vegetation is formed mainly due to the moisture factor against the background of the constancy of the edaphic and climatic conditions of the habitats. The communities of class Isoëto-Nano-Juncetea consist predominantly of species that have a wide eco-coenotic amplitude (generalists and semi- generalists according to Novosad and Krytska (2010)). The main fragments of their coenotic distribution are in the space of classes Phragmiti-Magno-Caricetea, Molinio-Arrhenetere- tea and Scorzonero-Juncetea. It should also be noted that in communities of the annual wetland vegetation, such species are represented either by special forms or by the pregenera- tive age stages. The role of species with narrow coenotic am- plitude (specialists and semi-specialists) increases in the spa- tially restricted communities of the alliances Nano-Cyperion and Verbenion. The low value of total coverage and the mo- Fig. 5. Differentiation of phytocoenoses of the annual wetland herbs vegetation in the space of two discriminant functions according to the data of ecological analysis. Fig. 6. Distribution the annual wetland herb vegetation associa- tions in the multifactorial space. KOVALENKO O., KALISTA M. 162 ACTA BOT. CROAT. 78 (2), 2019 saic of the grass stand and the weakly expressed dominance in the studied communities contribute to the active intro- duction of alien species (alien species account for 14.42%), among which the most constant are Bidens frondosa, Cony- za canadensis and Iva xantiifolia. Some of the alien species have a high coenotic value and are therefore considered as diagnostic species, for example, Juncus tenuis for the alli- ance, Nano-Cyperion, Epilobium adenocaulon and Digitaria ischaemum for Verbenion supinae. It is interesting that such a status for them is also characteristic within the primary areas (Brullo and Minisalle 1998, Šumberová 2011). This analysis confirms the vulnerability of the annual wetland communi- ties to the factor of human pressure, as well as the abundant evidence of the radical transformation and elimination of Isoëto-Nano-Juncetea phytocoenoses in Western and Central Europe (Korneck 1960, Philippi 1968, Pietsch 1973, Popi- ella 1996, Šumberová 2011). The results of factor analysis are additionally against synonymization of Polygono-Junce- tum with Eragrostidetum suaveolentis as some authors pro- posed (Dubyna et al. 2016). The problem of determining the ceonoses of Nano-Cyperion, Radiolion and Eleocharition is obvious, at least at the regional level. The peculiarity of the association Eleocharito-Limoselletum is explained by the largest representation, and as a consequence, by the diver- sity of its communities on the territory of Pyriatynskyi NNP. Conclusions Analysis of the syntaxa of the annual wetlands vegeta- tion as multiparameter systems revealed a complex picture of their differentiation in a system of floral, ecological and geographic coordinates. The dendrogram of the floristic similarity of phytocoenes largely coincides with the early classification of vegetation of the class Isoëto-Nano-Juncetea developed for Pyriatynskyi NNP. The systematic and bio- morphological structure of the determined syntaxa is quite original due to the ecological and phenological uniqueness of the studied communities. According to the data of the syn- phytoindication, the leading factors of the variety of annual wetland communities are the soil, humidity and to a lesser extent, salt regime against the background of the constan- cy of the remaining ecological parameters. The geographic structure of the lower-level syntaxa is quite conservative and coincides with that for the class. Anthropogenic pressure on the communities of Isoëto-Nano-Juncetea cases increasing role of anthropophilic elements in the composition of the vegetation cover. As a consequence, the development of spe- cial measures for the protection of this unique type of veg- etation is necessary. A complex comparative study of Isoëto- Nano-Juncetea syntaxa analysis pointed on one hand to the critical nature of the distinction between the Nano-Cyperion and Eleocharion ovatae alliances and on the other hand con- firmed the acceptability of the Radiolion linoidis as a separate syntaxon, and the legitimacy of distinguishing associations Eragrostidetum suaveolentis and Polygono-Juncetum. In view of the above, we think that a large-scale study of the syntaxa of the annual wetland vegetation allows us to make a stable system of the Isoëto-Nano-Juncetea class and sheds light on many theoretical and practical problems in the classification of vegetation. 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