Chionophilous vegetation in the high alpine and subnival belts of the Pamir-Alai and western Tian Shan Mts. (Tajikistan and Kyrgyzstan)

e aim of this study was to complete the syntaxonomic scheme for the high alpine and subnival vegetation in the Pamir-Alai and western Tian Shan Mts. 303 relevés were sampled in 2013–2022 using the seven-degree cover-abundance scale of the Braun-Blanquet approach. e dataset was classified using the k -means algorithm. Diagnostic species were determined using the phi coeﬃcient as a fidelity measure. Diﬀerences between vegetation units were visualized using non-metric Multidimensional Scaling (NMDS). Fieen associations (13 newly described) and three rankless plant communities were distinguished, and grouped into three alliances: Oxytropido savellanicae-Nepetion pamiricae for high altitude subnival rupiculous and snow-bed vegetation, Stipo regelianae-Ptilagrostion malyschevii for chionophilous summit graminoid and dwarf-scrub mountain tundra in the alpine and subnival belts and Poo alpinae-Bistortion ellipticae for mesic grazed alpine pastures on fertile soils. e main factors diﬀerentiating the species composition of the researched vegetation are the mean diurnal temperature range, the sum of annual precipitation, precipitation seasonality, temperature of the driest quarter, and precipitation of the coldest quarter. Our study has expanded the knowledge of subnival snow bed, grassland, and rupiculous vegetation of the Pamir-Alai and western Tian Shan Mts. and contributed to the consistent hierarchical classification of vegetation in the region. However, further studies in neighboring regions such as the Hindu Kush, Kopet-dagh, or Altai Mts. are desirable to achieve a consistent classification of the high mountain grasslands


Introduction
Middle Asia is traditionally referred to Kyrgyzstan, Tajikistan, Uzbekistan, Turkmenistan, southern Kazakhstan, western China, and northern Afghanistan.Southern and eastern parts of Middle Asia encompass the high mountains of the Pamir-Alai and Tian Shan Mts., with a vast alpine belt occurring mainly above 2,600-3,000 m a.s.l.According to the ten-volume study of the flora of the former Soviet part of Middle Asia, more than 9,000 vascular plant species are known from this region (Khassanov, 2015).e species pool for grasslands only for Tajikistan includes approximately 2,000 species (about 1,350 in steppes, 370 in meadows and pastures, and 265 in alpine swards).Considering generally low endemism at high altitudes, Middle Asia, with 136 alpine and subnival narrow endemic taxa, clearly stands out in this regard.Middle Asia is recognized as one of the world's 35 hotspots of biodiversity (Mittermeier et al., 2011).In view of Only a few phytosociological surveys have been conducted on alpine and subnival vegetation from adjacent areas.Several grassland communities have been recorded in the alpine belt of the Altai Mts. of south-eastern Kazakhstan (Rubtsov, 1948).ey were included in high-altitude vegetation and called 'low-herb alpine grasslands' following the Russian classification approach.Traditionally named Kobresia-forb swards (with Kobresia capilliformis, K. humilis, Alchemilla retropilosa and Leontopodium fedtschenkoanum) and rupiculous alpine vegetation on fine debris (Dracocephalum imberbe, Saussurea glacialis, Rhodiola coccinea, Potentilla biflora, Oxygraphis glacialis, and Trollius altaicus) have been reported from the Altai Mts.(Dimeyeva et al., 2016;Rubtsov, 1948).Towards the main Himalayan chain, in eastern Ladakh, the Kobresia royleana-Kobresia schoenoides matts, and Poa attenuata-Potentilla pamirica grasslands were reported from elevations up to 5,700 m a.s.l.(Dvorskỳ et al., 2011).
In Alborz Mts., the alpine and subnival vegetation was defined as the Oxytropis persica-Catabrosella parviflora community group (Akhani et al., 2013).It inhabits a diverse range of ecological niches, including rupiculous, xerophytic, and hygrophilous habitats at approximately 3,500-4,000 m a.s.l.is chionophilous vegetation has already been mentioned by Klein (1982) in this region, who proposed the class Oxytropidetea persciae and the order Trachydietalia depressae for the snow-bed vegetation of the Middle East, which thrives at elevations of 3,100 to 4,350 m a.s.l.However, Noroozi et al. (2010) included this vegetation in the order Drabetalia pulchellae, which comprises three alliances: Astragalion iodotropidis, Cousinion multilobae, and Acantholimion demawendici.Generally, the floristic composition at genus rank is quite similar to the Pamir Alai alpine vegetation, with Astragalus, Alchemilla, Veronica, Oxytropis, Potentilla, Silene, Allium, and Cousinia as the richest genera (Noroozi et al., 2020).In this context, Klein's proposal to consider this type of nival vegetation in Middle Asia described by Ukacheva (1975) Oxytropeta immersae as vicariant to the Iranian subnival grasslands and swards seems very relevant.Additionally, Noroozi et al. (2010Noroozi et al. ( , 2017) ) distinguished three alliances (Astragalion polyanthi, Astragalion sahendi and Taraxaco brevirostris-Polygonion serpyllacei) for thorn-cushion grasslands and snow-bed vegetation, with 15 associations and one additional subassociation for the alpine and subnival belts of Sahand Mts., Sabalan Mts. and Bozqush Mts. in NW Iran.While the thorn-cushion vegetation is very distinct in terms of the floristic composition, the snow-bed vegetation shares a considerable proportion of taxa common to Middle Asia (e.g., Festuca alaica, Oxytropis savellanica, Kobresia schoenoides, Oxyria digyna, and Gnaphalium supinum).e same applies to the rupiculous habitats of the subnival belt, where among the most common taxa in the Alborz Mountains are those also known from the highest elevations of Middle Asia (e.g.Didymophysa, Draba, Dracocephalum, Erysimum, Lamium, Oxytropis, Paraquilegia;Noroozi et al., 2020).is vegetation was classified in the Didymophyso aucheri-Dracocephaletea aucheri class and the Didymophysetalia aucheri order for the Iranian territory (Noroozi et al., 2014).
To better understand the diversity and phytogeographical similarities of alpine and subnival grasslands, it is necessary to study them in detail in the central part of Asia, at the node of the great continental mountain chains meeting in Middle Asia and the Pamir.
In this paper, we attempt to classify the high alpine and subnival vegetation in the Pamir-Alai and western Tian Shan Mts. and relate it to the subalpine grasslands of this area.We aimed to address the following questions during our study: (1) What is the diversity of grassland plant communities of the alpine and subnival belts in the Pamir-Alai and western Tian Shan Mts? (2) What are the basic environmental conditions of the described plant communities?(3) What is the species composition and structure of the vegetation types?(4) Which species have important diagnostic value for the described syntaxa?

Study area
e vegetation survey was carried out in several ecoregions of Central Asia within the administrative boundaries of Kyrgyzstan and Tajikistan.e study area lies between latitudes of 37.485°and 42.483°, and longitudes of 68.237°a nd 79.124°, comprising a significant part of both countries.Most plots (139) were sampled in a hotspot of high-altitude vegetation in the Pamir alpine and desert tundra ecoregion (Dinerstein et al., 2017).Vegetation-plot data were also collected from other ecoregions: the Tian Shan montane steppe and meadows (97 plots) and from the transitional areas between the Tian Shan foothill and steppe and the Tian Shan montane conifer forests (67 plots).All these areas are part of two large systems of mountain ranges in Central Asia: the western Tian Shan and the Pamir-Alai Mountain system.Despite the wide spatial extent of the study area, we searched for accessible mountain ranges with the occurrence of habitats suitable for the development of alpine and subnival vegetation, which are found above treeline at altitudes between 2,600 and 4,800 m a.s.l.Study sites at lower altitudes are used by local societies as summer pastures for sheep and goats and less oen for horses and yaks.Areas near the snow line with sparse vegetation, are grazed sporadically, or grazing never occurs.Here, as elsewhere in the mountains, climatic conditions depend on altitude, but locally, the vegetation can be more affected by exposition and relief rather than by elevation.Local relief in the alpine and nival belts is crucial for the radiation, temperature, and water regimes.In addition, it determines the depth and duration of snow cover.e coupled effect of land relief and elevation on vegetation is oen more important than macroclimate, which is difficult to generalize for spatially distanced mountain ranges.Nevertheless, the common feature of all surveyed mountain ranges is that they are influenced by a relatively dry macroclimate with high continentality and the highest precipitation in summer.We expect high vegetation variability along environmental gradients considering high variation in macro-and micro-scale features of the surveyed mountain ranges, including mean annual air temperature (min: −13.1 °C, max: 7.6 °C, mean: −5.7 °C), annual precipitation (min: 181.5 mm yr −1 , max: 1,507 mm yr −1 , mean: 724.5 mm yr −1 ), and also in the number of days with snow cover (min: 110, max: 365, mean: 308) based on snowpack model by Paulsen and Körner (2014).

Data sampling and statistical analysis
e research was conducted in the years 2013-2022.Altogether, 303 relevés were collected in the Pamir-Alai (Tajik-istan) and western Tian Shan Mts.(Kyrgyzstan).e size of each vegetation plot ranged from 1 to 10 m 2 .In each plot, all vascular plant species and mosses were recorded using the seven-degree cover-abundance scale of the Braun-Blanquet approach.e geographical coordinates of each plot were recorded with the help of a GPSMAP 60CSx device with an accuracy of ±5 m, using the WGS84 standard.
Data were stored in the Vegetation of Middle Asia database (A.Nowak et al., 2017) and analyzed in R (R Core Team, 2023) and JUICE soware (Tichý, 2002).To understand the distribution of samples and the relations between them, we performed an unsupervised k-means analysis with the Hellinger transformation.e number of clusters was determined according to gap statistics using the clusGap function in the 'cluster' package (Maechler et al., 2019) in the R environment.e algorithm indicated 18 groups as the most optimal for the analyzed dataset, which corresponds well with our field experience.Diagnostic species for each group were identified using the phi coefficient as a fidelity measure (Chytrý & Tichý, 2003).e size of all groups was standardized to equal size, and Fisher's exact test (p < 0.05) was applied.e phi coefficient values were multiplied by 100.Species with a phi coefficient ≥ 40 and frequency > 20% were considered diagnostic for the associations, a threshold phi ≥ 30 was used for alliances and phi ≥ 25 for orders.Species with a frequency higher than 50% were defined as constant, and those with a maximum cover value exceeding 30% were defined as the dominant species of an individual community.For alliances and orders, the threshold for constant species was frequency > 40% and for dominant > 50%.Non-metric multidimensional scaling (NMDS) based on Euclidean distance was performed to assess floristic relationships among the classified vegetation types using the function metaMDS in the 'vegan' package (Oksanen et al., 2019).Prior to the analysis, all cover values of the Braun-Blanquet scale present in the analyzed dataset were transformed to a percentage scale (+, 1, 2, 3, 4 to 2%, 3%, 13%, 38%, 63% respectively) and log(x + 1) transformed.e final ordination was run with 999 random starts using three dimensions (stress value = 0.199).Next, we fitted bioclimatic variables post hoc to the ordination axes to explore their associations with each vegetation type using the function envfit with 999 permutations in the 'vegan' package (Oksanen et al., 2019).Climatic data were extracted from the CHELSA database version 2.1 (http://chelsa-climate.org; Karger et al., 2017).Prior to analysis, correlations between 19 bioclimatic variables were calculated using the Spearman correlation coefficient to reduce the number of available variables.Variables indicating strong multicollinearity (r > 0.75 in all pairwise comparisons) were removed, and we retained variables most clearly interpretable from an ecological point of view.e climatic variables used for analysis were mean annual temperature, mean diurnal temperature range, mean temperature of the wettest quarter, mean temperature of the driest quarter, annual precipitation, precipitation seasonality, and precipitation of coldest quarter.
A shortened synoptic table with the fidelity and relative percentage frequency of all diagnostic species and other species with frequency ≥ 20% is shown in Table 1.An analytic table including type relevés (Table S1) and a full synoptic table (Table S2) are available in the Figshare Digital Repository  (Table S2) (1995).e plant material collected during field studies was deposited in the Herbarium of Middle Asia Mountains, hosted in OPUN (University of Opole, Poland) and KRA (Jagiellonian University, Poland).

Classification of the vegetation units
We identified 18 communities from three classes of high alpine and subnival vegetation: Didymophyso aucheri-Dracocephaletea aucheri (groups 1-10), Carici rupestris-Kobresietea bellardii (group 11), and Festucetea alaico-krylovianae (groups 12-18) in Tajikistan and Kyrgyzstan (Figure 1).e classification results were fitted to NMDS ordination (Figure 2), and the shortened synoptic table is presented in Table 1.e first axis of the NMDS reflects a substantial mean diurnal air temperature range-precipitation gradient.e plots that were classified into high altitude subnival rupiculous and snow-bed vegetation (groups 1-10) of the order Drabo pamiricae-Androsacetalia akbaitalensis are associated with a higher temperature range of temperatures and a lower sum of annual precipitation compared to the plots classified as mesic alpine pastures (groups 12, 14, 15 and 18) of the order Geranio saxatilis-Festucetalia alaicae.e second axis is linked with mean temperature of the driest quarter and precipitation of the coldest quarter, where higher values of these bioclimatic variables differentiate Littledaleo alaicae-Stipetum trichoidis, Poo bucharicae-Oxytropidetum savellanicae and Drabo alajicae-Omalothecetum supinae associations from other communities within class Festucetea alaico-krylovianae.e outlier in the lower part of the diagram is the association Violo thianschanicae-Stipetum regelianae -the chionophilous summit graminoid and dwarf-scrub mountain tundra in the alpine and subnival belts that occupies the habitats with higher precipitation seasonality.

High altitude subnival rupiculous and snow-bed vegetation
Class: Didymophyso aucheri-Dracocephaletea aucheri Noroozi et al. 2014   3A).e association develops on slopes with varying exposures but mostly with a north-western aspect.e inclination of the slopes ranges from 12°up to 90°(mean = 75°; Figure 3B).e vascular species richness of this phytocoenosis is low and ranges from three to 12 taxa per plot (on average six; Figure 3D), and the cover of the herb layer is from 10 to 45% (average of about 25%; Figure 3F).Mosses also appeared on plots ranging from one to three with coverage up to 35% (Figure 3E, Figure 3G).3A) in the Jeti-Ögüz district of the Issyk-Kul region in north-eastern Kyrgyzstan.e number of vascular plant species ranges from five to 11 with a mean of eight (Figure 3D), and the cover of the herb layer of approximately 35% (Figure 3F).e vegetation is singlelayered, and no mosses were found.e final classification and assignment of this community requires more data from Leiospora bellidifolia and Ajania trilobata distribution ranges.is association develops on steep slopes with an inclination of 45°to 80°(mean = 64°; Figure 3B), most oen with a north-western and northern exposure, at alpine elevations ranging from 4,115 to 4,343 m a.s.l.(mean = 4,287 m a.s.l.; Figure 3A).e patches of this vegetation are species poor with three to 10 species per plot (mean = 7; Figure 3C).e cover of the herb layer is relatively low and ranges from 20 to 55% (average about 29%; Figure 3F).3A), most oen on the south-western, southern and south-eastern slopes with an inclination of about 15°-85°(mean = 61.5°; Figure 3B).e richness of vascular plant species is low, with 4 to 12 taxa per plot (mean = 6; Figure 3C).Mosses are not very important in the phytocenoses, with one to three species with low coverage (Figure 3E, Figure 3G).e mean value of the herb cover is about 45%, ranging from 35% to 65% (Figure 3F).3B), mostly with a south-western exposition, at an altitude of 2,687 to 3,003 m a.s.l.(average 2,832 m; Figure 3A).e number of vascular plant species in a plot ranges from six to 11, with a mean of 10 (Figure 3D).e mean value of the herb cover is 36% ranging from 20% to 65% (Figure 3F), and the cover of the moss layer varies between five to 15% (average 8%; Figure 3G).(mean = 3,420 m a.s.l.; Figure 3A) with varying slope aspects, most oen western, north-western, northern, and northeastern.e inclination of slopes ranged from 2°to 95°(mean = 67°; Figure 3B).e number of vascular plant species ranges from three to 21, with a mean of 10 (Figure 3D).e cover of the herb layer ranges from 15 to 70% (mean = 33%; Figure 3F).Noteworthy is the presence of mosses with a maximum cover of 10% (on mean = 3%; Figure 3G).Figure 3A).e community was noted mainly on the northeastern and north-western slopes at varied inclination from 5°t o 85°(Figure 3B).e cover of the herb layer ranges from 25 to 75% (Figure 3G).Plots were consisted of four to 13 species, with an average of approx.eight (Figure 3C).3A).Plots of this association were found mainly on the south-western and southern slopes with varying inclinations from 45°to 80°(mean = 64°; Figure 3B).Despite subnival elevation, this area is characterized by low annual precipitation.Species richness is low, with only  region).e association forms alpine and subnival patchy swards at elevations of 3,107-4,315 m a.s.l.(Figure 3A).It inhabits slopes with an average inclination of approx.45°, ranging from 3°to 95°(Figure 3B), most oen with a north-western and western aspect.e number of vascular plant species varies between five and 22, with a mean of 10 (Figure 3D).e total cover of the herb layer in the plots ranges between 15% and 95% (average approximately 42%; Figure 3F).Floristic and habitat characteristics: Acantholimonetum diapensioidis can be defined as alpine cushion vegetation that develops on the gentle slopes of the Kyrgyz Ala-Too range in the North Tian-Shan (N Kyrgyzstan) and on the gentle slopes and flattened barelands of the Eastern Pamir (e.g.Shugnan Mts., Muzkol Mts.).e association occurs on slopes of various exposures with an inclination of 3°to 20°(Figure 3B) at altitudes from 3,070 to 4,660 m a.s.l.(Figure 3A).e species richness is low, with 3-13 species per plot (Figure 3C).

Group of tussock and cushion subnival and alpine vegetation
e cover of the herb layer ranges from 20 to 80% (Figure 3F).e vegetation is single-layered with no mosses.3A) with varying slope exposures in north-eastern Kyrgyzstan.e inclination of the slopes was low and ranged between 3°and 35°(mean = 18°; Figure 3B).e patches were relatively rich and harbor 16 to 27 species in a particular relevé (Figure 3C).e cover of the herb layer ranges from 45 to 95%, with a high mean of more than 80% (Figure 3F).e cover of the moss layer was rather low, occasionally reaching up to 25% (Figure 3G).

Mesic grazed alpine pastures on fertile soils
Order: Geranio saxatilis-Festucetalia alaicae S. Floristic and habitat characteristics: Papavero crocei-Ranunculetum popovii forms patchy alpine grasslands used as pastures at altitudes from 3,119 to 3,477 m a.s.l.(Figure 3A) on flattened areas of hilltops and passes of the Terskey Ala-Too range south of the Issyk-kul Lake (NE Kyrgyzstan) and the Alai range (SW Kyrgyzstan), as well as on the gentle slopes of the Kyrgyz Ala-Too range in the North Tian-Shan (N Kyrgyzstan).It prefers south-eastern exposures and inconsiderable slope inclinations of approximately 2°to 15°(Figure 3B).Both, species richness and cover of the herbaceous layer are relatively high.From eight to 27 species were recorded in sampled plots (mean = 20; Figure 3C).e cover of the herb layer ranged from 40 to 95% (average above 70%; Figure 3F).Noteworthy is the presence of mosses with a cover of up to 10% (Figure 3G).3A) with a gentle inclination of slopes from 2°to 15°(mean = 5.5°; Figure 3B), most oen with a north-western exposure.e cover of the herb layer ranges from 60 to 85%, with a mean of 70% (Figure 3F).e species richness is fairly low, ranging from six to 13 species per plot (average 10; Figure 3C).Floristic and habitat characteristics: Bistorto ellipticae-Pedicularietum korolkowii is an alpine grassland that serves as summer pasture mainly for sheep.is association has been recorded on gentle slopes of the Kyrgyz Ala-Too range (Chüy and Naryn regions in northern Kyrgyzstan) at heights ranging from 3,145 to 3,392 m a.s.l.(mean = 3,268 m a.s.l.; Figure 3A) with varying inclinations from 2°to 30°(mean = 10°; Figure 3B).is vegetation grows on slopes with different exposures, mainly north-east.e cover of the herb layer ranges from 60 to 90%, with a mean close to 80% (Figure 3F).e species richness is the highest compared to the other vegetation types, ranging from 16 to 30 species per plot (mean = 22; Figure 3C).an average inclination of approx.9°(Figure 3B), most oen with a south aspect.Plots comprised nine to 24 species, with a mean of 18 (Figure 3C).e cover of the herb layer ranges between 45 and 100% (mean = 80%; Figure 3F).Mosses form a distinct layer reaching up to 20% (Figure 3G).3A).is vegetation prefers the north-eastern aspect with a gentle inclination from 2°to 20°(mean = 13°; Figure 3B).e cover of the herb layer varies from 45 to 90% (mean = 74%; Figure 3F), and the species richness is moderate, ranging from nine to 17 species per plot (average 12; Figure 3D).is vegetation is used as summer pasture for grazing sheep.Floristic and habitat characteristics: e community of Trollius komarovii-Erigeron heterochaeta can be defined as alpine wet grassland.Patches of this phytocoenosis were found in north-eastern Kyrgyzstan in the Ak-Suu and Jeti-Ögüz districts on flatlands and the gentle slopes of the Terskey Ala-Too range east and south of Lake Issyk-kul, at altitudes of 2,615 to 3,842 m a.s.l.(Figure 3A).is vegetation develops mainly on the north-western slopes with a slight inclination of five to 15°(mean = 11°, Figure 3B) or flatlands.e mean cover of herbs is 45% (ranging from 30% to 80%; Figure 3F), and the richness of vascular species raging from seven to 29 species per plot (mean = 15; Figure 3D).(Afanasjev, 1956;Sidorenko, 1971;Swacha et al., 2023;Świerszcz et al., 2023).In the recent work on alpine grasslands in Middle Asia (Swacha et al., 2023;Świerszcz et al., 2023), 13 plant communities were distinguished within three alliances (Aconito rotundifolii-Potentilion pamiroalaicae, Stipo regelianae-Ptilagrostion malyschevii and Artemision dracunculi).ey are mainly adjacent to forb steppes in lower alpine and subalpine locations or mountain desert steppes or cryophilous steppes in lower rainfall zones, e.g., the Eastern Pamir (A.Nowak et al., 2021Nowak et al., , 2023)).Several grassland communities have been recorded in the alpine belt of Altai Mts. of south-eastern Kazakhstan (Rubtsov, 1948) (Dimeyeva et al., 2016;Rubtsov, 1948).e majority of these species also occur in western Middle Asia.In our opinion, these communities are very similar to the alpine and subnival vegetation types in Tajikistan and Kyrgyzstan.For example, communities dominated by Dracocephalum imberbe, Poa alpina, Geranium saxatile, or Festuca alaica.erefore, we decided to merge the high-altitude grasslands of western Middle Asia (Pamir-Alai, W Tian Shan) and Central Asia (Altai) into one class; however, this requires further comparative studies to reach the final consistency.Such a pattern of distribution shows that the forb steppe vegetation (dominated by Irano-Turanian plants), approaches from the south-west into the mountains of Middle Asia up to the subalpine belt, while from the opposite direction, from the north-east, the temperate climate vegetation (Euro-Siberian) forming alpine and subalpine grasslands "overlays" the alpine and subnival belts.

Discussion
However, towards the south, especially in the drier areas surrounding the eastern Pamir (e.g., Alaian, Zaalaian, Fergana, Shugnan Mts.), this general SW-NE pattern changes somewhat along the phytogeographical borderline between Middle and Central Asia.Rainfall values are decreasing, resulting in the fact that, despite very high altitudes, species of Irano-Turanian origin dominate.Characteristic 'dry alpine grasslands' are formed (e.g., Dracocephaletum imberbe or Nepeto pamiricae-Rhodioletum recticaulis), or cushion communities (e.g., Acantholimonetum diapensioidis) which have low biomass production and sparse cover.ey are similar to the high alpine rupiculous vegetation of Alborz Mts. in terms of functional, life-form, and oen taxonomic composition (Oxytropido persicae-Cousinietum multilobae; Noroozi et al., 2010).In this case, combining these vegetation types in one large unit at the class rank seems reasonable (Klein, 1982;Ukacheva, 1975 (Breckle & Rafiqpoor, 2020).
In the Karakorum and the western Himalayan range, in Eastern Ladakh, the Kobresia royleana-Kobresia schoenoides matts, and Poa attenuata-Potentilla pamirica grasslands have been reported from elevations up to 5,700 m. (Dvorskỳ et al., 2011).ey are similar to high mountain matts in physiognomic terms but also in terms of species richness, composition, and vegetation structure.Perhaps the only difference is that the matts of the western Himalayas are mainly grazed by yaks, while in the western Tian Shan they are mainly grazed by horses.

Variability and internal relations of high alpine and subniwal vegetation of Middle Asia
e vegetation of the highest mountain altitudes in Middle Asia is very diverse and, to some extent, heterogeneous.is is caused by a diverse, harsh environment that is characterized by extremely high-temperature amplitudes and the lowest minimum temperature in winter up to −60 °C, and also by high solar radiation, particularly UV-B radiation that can be 100% more intense than in the valleys (see Leuschner & Ellenberg, 2017).Moreover, the daily frost, even in summer, scarce soils, low nutrient availability combined with solifluction, long-lasting and deep snow cover, slabs, avalanches, landslides, and strong winds make this area one of the most unfavorable for plant life.is extremely harsh environment is responsible for controlling and filtering the species that need to adapt to these extremes despite the type of substrate that is not so crucial (e.g., calcicole or calcifuge).erefore, it is oen difficult to distinguish between scree habitats, chasmophytic ledges, and desert steppes at very high elevations.Some associations can occupy two or even three different habitat types (e.g., Dracocephaletum imberbe), but have an optimal habitat only in one.is causes considerable difficulty in distinguishing between these plant communities.However, with certainty, the high mountain vegetation of Middle Asia can be divided into In places with a more nutrient-rich habitat and slightly better-developed and hydrated soils, graminoid matts dominate on gentle slopes, passes, and hilltops.Generally, in Middle Asia, they are composed mainly of species of the genus Kobresia.ey form dense and widespread matts with dominance of species such as S. regeliana as well as Ptilagrostis malyschevii and Stipa tremula (the two later species replace here P. dichotoma and S. purpurea that occur in Himalaya and Tibet; Nobis et al., 2022), that is present in our dataset and forms a distinct Violo tianschanicae-Stipetum regelianae.
Another group is formed by vegetation of slightly lower altitudes, which belong to typical alpine grasslands (Swacha et al., 2023).ey include several distinct groups and occur mainly in the Tian Shan ranges.Some of these communities have sparse physiognomy of graminoid swards (Papavero crocei-Ranunculetum popovii, Littledaleo alaicae-Stipetum trichoidis, Poo bucharicae-Oxytropidetum savellanicae), whereas other form relatively dense carpets and resemble species rich, compacted short-grass vegetation of the alpine zone (Bistorto ellipticae-Pedicularietum korolkowii, Trollius komarovii-Erigeron heterochaeta community).Two communities in this group are associated with wetter habitats that occur adjacent to moraines' foot, flat snow beds, or sloping water outlets.ese are Poo attenuatae-Callianthemetum alatavici and Drabo alajicae-Omalothecetum supinae.It cannot be ruled out that the syntaxonomic position of the latter two vegetation types will change in the future aer collecting more data.

Conclusions
Our study has expanded the knowledge of subnival snow bed, grassland, and rupiculous vegetation in the Pamir-Alai and western Tian Shan Mts. and contributed to the consistent hierarchical classification of vegetation in the region (A.Nowak et al., 2016a;Swacha et al., 2023;Świerszcz et al., 2023).Similarly to the vegetation of screes, cryophilous or forb steppes, or alpine grasslands (A.Nowak et al., 2016bNowak et al., , 2021;;Świerszcz et al., 2023), the heterogeneity of this subnival vegetation is evident.e Central Tian Shan is strongly influenced by a temperate climate and Euro-Siberian flora (thus the solid relation for Altai vegetation), while the southernmost limits of the eastern Pamir are compositionally related to the Irano-Turanian region.An additional strong gradient that influences the diversity of subnival and alpine vegetation of Central and Middle Asia is the humidity, which decreases from the snow bed, moraines, through mountain slopes with moderate moisture content to rupiculous and almost semi-desert plateaus in the Eastern Pamir, which are arid.Grasslands are additionally influenced by different grazing intensities, which is a crucial factor throughout Middle Asia.It has the greatest impact on alpine grasslands and isis much less significanton low-productive vegetation at the highest altitudes.
is study summarizes our grassland surveys in Middle Asia; however, it would still be helpful to conduct further surveys, especially in neighboring regions such as the Hindu Kush, Kopet-dagh, and Altai Mts., to obtain a stable and internally consistent syntaxonomical system of grassland communities.
Oxyria digyna community is an alpine and subnival rupicolus vegetation recorded in the western Tian Shan Mts. in the Jeti-Ögüz district of the Issyk-Kul region (north-eastern Kyrgyzstan), in the Kochkor district of the Naryn region (north-central Kyrgyzstan) and in the Pamirs in Gorno-Badakhshan region (eastern Tajikistan) at elevations of 3,280 to 4,011 m a.s.l.(mean = 3,714 m a.s.l.;

Floristic
and habitat characteristics: Poo attenuatae-Callianthemetum alatavici can be classified as alpine snow-bed vegetation.is association has been sampled in north-eastern Kyrgyzstan in the Jeti-Ögüz district of the Terskey Ala-Too range at an altitude of 3,128 to 3,896 m a.s.l.(mean = 3,750 m a.s.l.; Figure3A).It grows on gentle slopes or flatlands with

Table 1
Shortened synoptic table with percentage frequency and fidelity values.Only diagnostic species are given and other species with frequency ≥ 20%.See supplementary material 2 for the full version of this table

Chionophilous summit graminoid and dwarf-scrub moun- tain tundra in the alpine and subnival belts Alliance: Stipo regelianae-Ptilagrostion malyschevii A. Nowak et al. 2023 e
alliance includes compact and short alpine and subnival grasslands in relatively moist habitats and long-lasting snow cover.eyareusedaspastures for horses and yaks.evegetationbelonging to this alliance is dominated by graminoids, mainly Kobresia spp., Stipa spp., Poa spp, Carex spp.e patches of Stipo regelianae-Ptilagrostion malyschevii occupy elevations of approximately 2,500 to 3,500 m a.s.l.(Figure3A) and have moderate species richness compared to other alpine vegetation in the study area (mean = 14; Figure3C).

Nowak et al. 2024 ord. nov. hoc loco Nomenclatural type:
Poo alpinae-Bistortion ellipticae S.Świerszcz et al. 2023hoc locoGeneral remarks: is order comprises alpine short grasslands of the eastern Irano-Turanian region, including Middle and Central Asia.e communities of this order form dense stands of graminoids, mainly Carex spp., Festuca spp., Trisetum spp., and Poa spp., as well as short forbs, e.g.Erigeron spp., Gentiana spp., Potentilla spp., Ranunculus spp., Cerastium spp., and Primula spp.e grasslands serve as summer pastures for sheep and horses, rarely yaks.Alpine belt of the northern and eastern ranges in the Irano-Turanian region (mainly Kyrgyzstan, northern Tajikistan, Kazakhstan, Xinjang in China).Mts., preferably on the northern slopes.eyareusedaspastures,especiallyfor sheep, and less oen for yaks, horses, and goats.Patches belonging to this alliance are generally characterized by high species richness and high cover of herbs and mosses (Figure3C, Figure3F-G) compared with the other two alliances.TableS1, relevé number 189, holotypus hoc loco.
(Noroozi et al., 2020)t al., 2020)zi et al. (2014)-Didymophyso aucheri-Dracocephaletea aucheri.Being typical Middle Asian subnival vegetation, these communities inhabit rupiculous and xerophytic habitats at approximately 3,500-4,500 m a.s.l.ey are composed of many common taxa, particularly at the genus rank, with Astragalus, Alchemilla, Allium, Cousinia, Didymophysa, Nepeta, Oxytropis, Potentilla, Silene, and Veronica as the richest genera(Klein, 1982;Noroozi et al., 2020).In particular, the snow-bed vegetation (Taraxaco brevirostris-Polygonion serpyllacei) in northern Iran shares a considerable proportion of common taxa with Middle Asia with Festuca alaica, Oxytropis savellanica, Kobresia schoenoides, Oxyria digyna, and Gnaphalium supinum as the most prominent.In addition, the name-giving species of this group (Polygonum serpyllaceum and Taraxacum brevirostre) are common in the highlands of Pamir-Alai (A.Nowak et al., 2020).T. brevirostris is replaced or supplemented by closely related species, such as T. minutilobum, T. pseudobrevirostre, T. kovalevskiae, T. schugnanicum, and T. murgabicum, which make the physiognomy of the vegetation very similar.Although, with lower rainfall compared to NW Iran, especially in the Pamir, the snow-bed vegetation of the Pamir Alai is definitely more rupiculous in character, probably more similar to those from the drier subnival belt of the Zagros Mts.where communities with Polygonum serpyllaceum were also noticed(Noroozi et al., 2020).e same applies to the rupiculous habitats of the subnival belt, where among the most common taxa in the Alborz Mts. are those also known from Middle Asian highest elevations (e.g., Ukacheva (1975)n that our dataset contains little data corresponding to low, patchy alpine grasslands composed mainly of Oxytropis immersa (high share only in Papavero crocei-Ranunculetum popovii), we decided not to followUkacheva (1975)and validate the unit of Oxytropeta immerse but e close geographical proximity and landscape similarities with a large area of alpine and subnival belts means that the described vegetation has much in common with the high mountain communities of the northern Hindu Kush.It shares numerous alpine species with the Pamirian plateau, including Waldheimia tridactylites, Saussurea glacialis, Aulacospermum stylosum, Psychrogeton andryaloides, Saussurea gnaphalodes, 3-4 main groups.e first is subnival rupiculous vegetation, including Violo acutifoliae-Potentilletum biflorae and Dracocephaletum imberbe in central Tian Shan, Carici stenocarpae-Androsacetum akbaitalensis, Achoriphragmetum pinnatifidi, Leiospora bellidifolia-Ajania trilobata comm., Nepetetum longibracteatae, and Nepeto pamiricae-Rhodioletum recticaulis in the Pamir and Alai ranges.Additionally, into this group was classified the Dracocephaletum nodulosi-Rosularietum borissovae from the lower alpine belt of the central Tian Shan and Oxyria digyna community, which occupies snow beds.Patches of this community are widespread in the Eastern Pamir and inhabit wet snow beds but also gentle slopes with a well-hydrated soil profile.Towards the drier sites, the Acantholimon diapensiodes community gives way to typical cushion-tragacanthic vegetation growing on underdeveloped soils with Acantholimon spp. or Oxytropis echidna.is cushion-tragacanthic vegetation oen has a patchy physiognomy and occurs in a mosaic with cryophytic desert steppes formed by Stipa orientalis and S. glareosa.

Table S2 .
Synoptic table of the high alpine and subnival vegetation of the Pamir-Alai and western Tian Shan Mts.e phi coefficient values (in superscript) in the table are multiplied by 100.Main values are species frequencies (in percentages).