Research Paper |
Corresponding author: Sebastian Świerszcz ( seb.swierszcz@gmail.com ) Academic editor: Idoia Biurrun
© 2022 Sebastian Świerszcz, Grzegorz Swacha, Małgorzata W. Raduła, Sylwia Nowak.
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:
Świerszcz S, Swacha G, Raduła MW, Nowak S (2022) Distribution of graminoids in open habitats in Tajikistan and Kyrgyzstan. Vegetation Classification and Survey 3: 273-286. https://doi.org/10.3897/VCS.95767
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Aims: Landscapes of Middle Asia are exposed to human influence due to long-lasting pastoral tradition, and now are largely dominated by non-forest vegetation. Graminoids perform key ecosystem functions, and constitute an important feed source for livestock. We studied the distribution patterns of graminoids cover under climatic and grazing pressure gradients in different open vegetation types. Study area: Tajikistan, Kyrgyzstan. Methods: 1,525 vegetation plots representing five open vegetation types (mires, salt marshes, tall-forb communities, pseudosteppes and steppes) were extracted from the Vegetation of Middle Asia Database. We assessed the relative cover of graminoid species in each vegetation type. The importance of mean annual temperature, sum of annual precipitation, aridity and livestock density as drivers of relative cover of graminoids contribution patterns in the five vegetation types were explored with use of polynomial functions and commonality analysis. Results: Open ecosystems of Middle Asia are characterized by different graminoid contributions. The highest relative cover of graminoids was found for steppes, pseudosteppes and mires. Comparison of model fits for relationship between the graminoids cover, climatic parameters and livestock pressure indicated advantage of polynomial models. The best-fitting models for pseudosteppes were for mean annual temperature, Aridity Index and livestock density, for steppes mean annual temperature and Aridity Index, and for salt marshes mean annual temperature. For mires and tall-forb communities, the models showed a poor fit or no effect of the variables studied. Conclusions: Our study shows that climate and livestock pressure have an impact on the contribution of graminoids in open vegetation types, but a general pattern is difficult to describe. Ongoing climate change may influence the share of graminoids in salt marshes, steppes and pseudosteppes. Grazing (with a common effect of climatic factors) is the most important factor influencing graminoids contribution on pseudosteppes, confirming the secondary origin of this vegetation type.
Taxonomic reference: The nomenclature of the vascular plants follows Plants of the World Online (
aridity, climate, Cyperaceae, grassland, hot-spot, Juncaceae, Kyrgyzstan, Middle Asia, open habitat, Poaceae, steppe, Tajikistan
Graminoids are a major component of open habitats across the world, particularly wetlands and grasslands (
Many grasses, sedges and rushes are effective colonisers, making them cosmopolitan (
Due to its unique floristic richness, most of the territory of Tajikistan and Kyrgyzstan is recognized by Conservation International as a biodiversity hotspot – Mountains of Central Asia (
About 9,300 vascular plant species have been described from the Middle Asia region (
In terms of food and economic safety, Middle Asia is almost entirely dependent on livestock production. This region has a long tradition of pastoralism and since ancient times a whole human population consider its welfare with the quality of pasturelands and the number of livestock herds. Besides typical grasslands, there are also other vegetation types in Middle Asia such as tall-forb communities, mires, and salt marshes used for grazing in which graminoids are likely key contributors to biomass and diversity. Thus, finding basic patterns of graminoid species abundance and distribution in different vegetation types in Middle Asia is of high importance. In this paper, we addressed three main questions: (1) How is graminoid species richness shaped in the open vegetation types of Tajikistan and Kyrgyzstan? (2) Is there a general pattern of graminoid occurrence in different open vegetation types? (3) How do climate and livestock density affect the proportion of graminoids?
The study was conducted within the administrative borders of Tajikistan and Kyrgyzstan (Figure
The region is characterized by a very long elevational gradient ranging from 287 to 7,495 m a.s.l, which makes this territory particularly diverse in terms of climate, land relief and geomorphology. The geological profile is complex with a predominance of limestone, marble, dolomite, dolomitic shale, clay shale, phyllitic schist, siltstone, and argillaceous slates of Carboniferous, Cambrian, Silurian, and Early Cretaceous origin. However, the specific geological conditions of this region are still under study (
The study area is difficult to characterize in terms of climatic conditions. The climate differs spatially in terms of its continentality, topographic complexity, and orography. However, according to
The warm and continental Irano-Turanian region (Fergana Valley and south-western Tajikistan) is characterized by low annual precipitation with the sum of ca. 200–250 mm, and the peak in March (ca. 80 mm). During the summer months (from June to August) the precipitation is scarce, with the sum of 0–10 mm per month. Snow and frost occur only in winter (from December to February). Temperatures strongly vary during the year; in the warmest months, they reach from 20°C (May) to 34°C (June, July, August). In winter, the mean temperature is no lower than -3°C with extreme values reaching -27°C in some years.
The warm, humid and continental region includes the Tian Shan and Pamir-Alai ranges. The sum of annual precipitation ranges from ca. 500 mm in northern slopes to ca. 1000 mm in southern slopes. In June, the mean temperature in colline and montane belts reaches ca. 22°C while in alpine belts, it reaches up to 10°C.
The cold, semi-arid region includes the Issyk-Kul basin, central and western parts of the Alai Valley, as well as foothills and plateaus in the colline, montane and subalpine belts. The area is characterized by low precipitation, with the sum of ca. 200–400 mm per year. The precipitation reaches a peak of 70 mm per month in spring (from May to July). The annual mean temperature is ca. 10°C, it exceeds 20°C only in the summer months.
The cold and arid climate region includes the easternmost sections of the Alai Valley and the eastern Pamirian Plateau. The sum of annual precipitation is extremely low and does not exceed 100 mm. Only in May and August the monthly sum of precipitation is ca. 20 mm. The annual mean temperature is slightly above 0°C, with a minimum of ca. -30°C from January to February.
The primary source of data was the Vegetation of Middle Asia database (
Photos of the open vegetation types: (a) steppe (Kosh-Dobo, Kyrgyzstan), (b) salt marsh (Zoogvand, Tajikistan), (c) pseudosteppe (on the right site of the photo; Khoja Mumin Mt. near Vose, Tajikistan), (d) tall-forb community (near Rabot, Tajikistan), (e) mire near Jelondy (Tajikistan) and (f) overgrazing – one of the main human-driven threats to grasslands in Middle Asia leading to land degradation.
Vegetation types | Number of plots | Plot size range (m2) |
---|---|---|
Mires | 489 | 2–30 |
Tall-forb communities | 168 | 10 |
Pseudosteppes | 150 | 10 |
Salt marshes | 191 | 10–100 |
Steppes | 527 | 10–30 |
The final data set consisted of 1,525 vegetation-plot records of open habitats (Table
We assessed the importance of mean annual temperature, sum of annual precipitation, aridity, and livestock density (surrogate of grazing intensity) as drivers of the relative cover of graminoids. Mean annual temperature and sum of annual precipitation are two key climate factors that determine plant distribution (
Based on the coordinates, we derived the mean annual temperature and the sum of annual precipitation from the CHELSA dataset, with a resolution of 0.00833 decimal degrees (30 arc sec;
All statistical analyses were performed in R environment (
We used linear models to explore the effects of the mean annual temperature, sum of annual precipitation, Aridity Index and livestock density for the patterns of graminoid abundance in open habitats. We performed linear models and evaluated the relevance of a quadratic term (polynomial) to account for potential curvilinear relationships. We built models for each vegetation type and explanatory variable separately. The best model among the linear and quadratic ones was evaluated by their coefficient of determination (R2) and root mean-squared error (RMSE) with the compare_performance function in the R package ‘performance’ version 0.8.0 (
Additionally, we used commonality analysis to find the most important factors influencing the contributions of relative cover of graminoids. To do this, we decomposed the variance of R2 into unique and common effects of predictors. Unique effects indicate how much variance is uniquely accounted for by a single predictor and common effects indicate how much variance is common to a predictor set (
In total, we recorded 255 graminoid species within all vegetation types. Graminoid-richest vegetation types were steppes (136 species – 53.3% of the total graminoid flora) and pseudosteppes (94 species – 36.9% of the total graminoid flora) (Table
Graminoid species cumulative number in each open vegetation type and the quantitative proportion of graminoids in relation to the graminoid flora (255 species). Grey-shaded cells show the number and percentage value (in brackets) of shared graminoid species between pairs of vegetation types. The darker the cell, the higher the number of shared graminoid species between pairs of vegetation types.
Total graminoid species richness = 255 | Mires | Tall-forb communities | Pseudosteppes | Salt marshes | Steppes |
---|---|---|---|---|---|
Mires | 77 (30.2) | 10 (3.9) | 24 (9.4) | 22 (8.6) | 13 (5.1) |
Tall-forb communities | 57 (22.4) | 41 (16.1) | 15 (5.9) | 40 (15.7) | |
Pseudosteppes | 94 (36.9) | 30 (11.8) | 61 (23.9) | ||
Salt marshes | 74 (29) | 26 (10.2) | |||
Steppes | 136 (53.3) |
The highest relative cover of graminoids was found for steppes (median: 47.8%), mires (median: 43.06%) and pseudosteppes (median: 39%). However, a particular density peak cannot be distinguished because the relative cover of graminoids is evenly distributed along the entire range within these vegetation types (Figure
Density curves representing the distribution of relative cover (%) for all graminoids together (a) and split by family (b, c, d) within open habitat types at plot level. The vertical red line shows the median value of relative graminoid cover within each vegetation type. On the y-axis, the distributions are represented by relative values with the maximum density of each group standardized to 1.
Model comparison showed that polynomial models provided a better fit for the relationship between graminoid relative cover and predictor variables (Table
The relationship between graminoids relative cover and mean annual temperature (MAT), sum of annual precipitation (AP), Aridity Index and livestock density for open vegetation types in Tajikistan and Kyrgyzstan. Lines are predictions of fitted polynomial models (for a comparison of linear and polynomial models see Suppl. material
Results of the polynomial regression models and commonality analysis for the effect of mean annual temperature, sum of annual precipitation, Aridity Index and livestock density on graminoids relative cover for open vegetation types. The significant values are shown in bold. Commonality analysis output represents a unique, common and total contribution of each predictor variable to the regression effect. The proportion of variance explained by the predictor is presented in parenthesis as a percentage of R2.
Explanatory variable | F | p-value | R2 | Commonality analysis | ||
---|---|---|---|---|---|---|
Unique | Common | Total | ||||
Mires | ||||||
Mean annual temperature | 1.20 | 0.303 | 0.005 | 0.001 (0.8%) | 0.004 (5.8%) | 0.005 (6.6%) |
Sum of annual precipitation | 13.30 | < 0.001 | 0.052 | 0.003 (4.6%) | 0.016 (22.3%) | 0.019 (27%) |
Aridity Index | 16.23 | < 0.001 | 0.063 | 0.033 (46.2%) | 0.028 (39.9%) | 0.061 (86.1%) |
Livestock density | 12.25 | < 0.001 | 0.048 | 0.003 (4.8%) | 0.025 (35%) | 0.028 (39.7%) |
Tall-forb communities | ||||||
Mean annual temperature | 0.82 | 0.441 | 0.010 | 0.003 (5.4%) | 0.005 (9.7%) | 0.008 (15.2%) |
Sum of annual precipitation | 4.26 | 0.016 | 0.049 | 0.037 (68.4%) | 0.003 (6%) | 0.04 (74.3%) |
Aridity Index | 1.16 | 0.316 | 0.014 | 0.013 (25.1%) | -0.002 (-2.8%) | 0.012 (22.3%) |
Livestock density | 0.88 | 0.417 | 0.011 | 0.004 (7.7%) | -0.004 (-7.3%) | 0.0002 (0.4%) |
Pseudosteppes | ||||||
Mean annual temperature | 13.31 | < 0.001 | 0.153 | 0.029 (11.1%) | 0.123 (46.4%) | 0.152 (57.5%) |
Sum of annual precipitation | 8.55 | < 0.001 | 0.104 | 0.004 (1.5%) | 0.07 (26.6%) | 0.074 (28.1%) |
Aridity Index | 14.40 | < 0.001 | 0.164 | 0.045 (17%) | 0.116 (43.9%) | 0.161 (60.9%) |
Livestock density | 22.69 | < 0.001 | 0.236 | 0.02 (7.4%) | 0.152 (57.4%) | 0.172 (64.9%) |
Salt marshes | ||||||
Mean annual temperature | 43.51 | < 0.001 | 0.316 | 0.239 (65.3%) | 0.068 (18.6%) | 0.307 (83.9%) |
Sum of annual precipitation | 7.56 | < 0.001 | 0.074 | 0.001 (0.2%) | 0.044 (11.9%) | 0.044 (12.1%) |
Aridity Index | 10.91 | < 0.001 | 0.104 | 0.004 (1.2%) | 0.078 (21.2%) | 0.082 (22.4%) |
Livestock density | 8.25 | < 0.001 | 0.081 | 0.031 (8.4%) | -0.003 (-0.8%) | 0.028 (7.6%) |
Steppes | ||||||
Mean annual temperature | 43.02 | < 0.001 | 0.141 | 0.0001 (0.1%) | 0.001 (0.4%) | 0.001 (0.5%) |
Sum of annual precipitation | 33.03 | < 0.001 | 0.112 | 0.013 (9.6%) | 0.085 (63.3%) | 0.098 (73%) |
Aridity Index | 42.06 | < 0.001 | 0.138 | 0.036 (26.6%) | 0.083 (62.1%) | 0.119 (88.6%) |
Livestock density | 25.31 | < 0.001 | 0.088 | 0.001 (0.7%) | 0.0002 (0.1%) | 0.001 (0.8%) |
The model showed that sum of annual precipitation had statistically significant effect on all vegetation types, although with a low model fit (R2 = 0.05–0.1; Table
Grasslands are generally described as vegetation dominated by graminoids, which typically have > 25% coverage (
The vegetation type with the highest proportion of graminoids are mires, which occur mostly in the mountainous areas of Middle Asia. Harsh environmental conditions at high elevational zones together with an intensive grazing promote species from the Cyperaceae. An increasing abundance of Cyperaceae representatives with increasing altitude was also found in the Himalayas (
Salt marshes and tall-forb vegetation had a low contribution of graminoids (median relative coverage < 25%, Figure
Grasslands in Middle Asia, despite having similar physiognomy, show high variation in species composition (
Steppes are typical grassland vegetation and constitute an important feature of the diverse landscape in Middle Asia. Our study showed strong response of graminoids relative cover to climatic gradients in these steppes. We observed a sharp decrease of graminoids at low average annual temperatures at altitudes above 3,000 m a.s.l. (own observations). With the increasing altitude and harsher environmental conditions, graminoids are replaced by resilient semi-desert taxa adapted to high elevations, e.g. Artemisia skorniakovii, Astragalus chomutowii or Braya pamirica (
The contribution of graminoids in salt marshes also varied along climatic gradients. The highest graminoid cover was found on sites with a low mean annual temperature, high precipitation and less arid conditions. Middle Asian salt marshes vary according to geobotanical regions. In south-western Tajikistan and in the Ferghana Valley salt vegetation inhabits e.g. shallow ponds and around riverbeds. The most common graminoid species is Aeluropus littoralis, however, it does not make a significant contribution to the vegetation. The high-elevation salt marshes in the Eastern Pamir are different. The vegetation is shaped by extremely harsh conditions and is species poor. However, a common feature of graminoid species found in salt marshes, as in steppes, is their longevity and low resistance to soil drought. Many vegetation patches are dominated by graminoids adapted to the high salt content in the soil, e.g. species of the genus Puccinellia (
Although our results show some patterns in the proportions of graminoids with regard to precipitation and the Aridity Index in mires, the models show a poor fit. The lack of a clear climatic gradient may be due to the fact that sedges are the main component of this type of vegetation (
Tall-forb communities are not typical graminoid vegetation. In most cases, graminoids do not dominate in these communities, although there is great variability within this type of vegetation (
The vegetation cover of open habitats in Tajikistan and Kyrgyzstan is strongly affected by livestock grazing, which resulted in changes in graminoid abundance. However, our study shows that not all analysed vegetation types respond to grazing in terms of graminoid contribution. We obtained the best-fitted model for pseudosteppes, where the proportion of graminoids increases with increasing livestock density to the highest point of all vegetation types analysed. The results confirm that pseudosteppes are a secondary vegetation type created after the cutting of pistachio groves (
Our study shows that the largest number of graminoid species is associated with steppes, which are the most common vegetation type in Middle Asia. However, there is no universal pattern for graminoid distribution along the climatic and grazing gradient, but such relationships were found for particular vegetation types. Strong but not consistent relationships were found in steppes, pseudosteppes and salt marshes. These differences result mainly from biogeographic features of the study area. But it is important to bear in mind that current and upcoming climate change may contribute to the potential extinction of some graminoid species, including endemics (
Primary data are stored in the Vegetation of Middle Asia database (http://www.givd.info/ID/AS-00-003) (
S.Ś. planned the research. S.Ś., G.S, and S.N. collected part of the field data. S.Ś. prepared the final dataset, performed statistical analyses and led the writing. G.S., M.R., and S.N. critically revised and edited the manuscript.
We are grateful to Idoia Biurrun, Arkadiusz Nowak, and anonymous Reviewers for the valuable comments that improved the quality of the manuscript. We also thank Firuza Illarionova from the Dushanbe Nature Protection Team for her assistance and help in organizing field expeditions. The project was partially supported by the National Science Centre, Poland, no. 2020/04/X/NZ8/00032.
Comparison of models performance used in our study
A list of graminoid species recorded in the study area