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Proglacial successions of springtail assemblages (Collembola) along retreating glaciers in Kabardino-Balkaria, Greater Caucasus, Russia
Since the end of the Little Ice Age, glacier retreat has been recorded globally, with its rates steadily increasing. Glacier forelands serve as convenient areas for studying the patterns of biotic community formation during primary succession. Collembola (hereinafter – springtails) typically play key roles in primary successions, being among the first colonists of territories newly freed from ice. The present study focuses on successional changes in springtail assemblages in the valleys of the Cherek-Khulamsky (Bezengi) and Adylsu along the Bezengi and Kashkatash glacier forelands, respectively (Kabardino-Balkaria, northern Caucasus). The Cherek-Khulamsky valley is located within the Kabardino-Balkarian High-Mountain State Nature Reserve, while the Adylsu valley is part of the Prielbrusye National Park. The objective of the present study is characterising the species composition and structure of springtail assemblages along the glacier chronosequences, as well as identifying the local features of the dynamics of these communities. Using standard soil zoological methods, we examined springtail communities across ten precisely dated plots (1–150 years since deglaciation) in both study valleys. On both locations, pioneer springtail complexes formed immediately after glacier retreat include specialised species, such as representatives of the nivalis group of the genus Desoria, which are replaced by widely distributed forms within 3–5 years. The dynamics of successional processes vary significantly between the Bezengi and Kashkatash glacier forelands. At Bezengi, the species richness has gradually increased, reaching a maximum after 135 years, whereas at Kashkatash, a sharp diversity increase is observed as early as 74 years since glacier retreat, at the shrub overgrowth stage. Springtail density also varies: at Bezengi it fluctuates from 36 individuals/dm2 to 177 individuals/dm2 , reaching the maximum values just 14 years after deglaciation (grassland stage), while at Kashkatash the first noticeable population increase up to 632 individuals/dm2 is recorded on 74-year old surfaces, with an absolute maximum (726 individuals/ dm2 ) achieved in 150-year old pine forests. The Kashkatash glacier foreland shows more pronounced differentiation between early (pioneer) and late (forest) successional stages than that of Bezengi, evident in both population abundance and species composition. At the same time, radical changes in springtail communities are observed in both valleys during transitions either from grasslands to shrublands or from shrublands to forests. Comparison with similar studies reveals a great role of the local features of a particular foreland. Regional differences could be accounted for by microclimatic, geomorphological and biotic factors. At Bezengi, where subalpine grasslands subject to anthropogenic influence predominate, succession seems to proceed more smoothly, while at Kashkatash the development of pine forests creates stable conditions favouring the formation of sustainable communities. Orographic features, such as slope steepness and the presence of rigels, also render a substantial impact, determining the environmental patchiness and the rate of successional changes. The data obtained contribute to understanding the patterns of biotic community formation in montane ecosystems under deglaciation and emphasise the need for further comparative studies to predict changes under global warming conditions.