Dynamics of the structural organization of steppe communities in Eastern Mongolia under changing climatic parameters

The investigation of the Eastern Mongolia steppes of three-feather formation (Stipa grandis, S. krylovii, S. sibirica) was carried out in 2008–2019 on 11 test plots of 100 m² each, located along a transect within the intermountain plain south of the Kerulen River valley. The structural organization of steppe communities is considered as a criterion for the sustainability of ecosystems under changing climatic conditions. It is determined by the ratio of life forms, i. e. biomorphological types of plants, identified by the adaptations to vegetative growth (vegetative mobile; growing vegetative weakly mobile; vegetative immobile and nongrowing), and the biomorphological groups (turf, root, rhizome, root proliferous, annual-biennial), as well as the composition of dominants and the species richness of communities. Deviance of bioclimatic indicators from the long-term average values (1962–1990) was determined for the period of observation. Combinations of the life forms of plants and changes in the structural organization of communities were revealed. The structure of communities was statistically verified between different years (ANOVA, Kruskal-Wallis test).
According to the change in moisture conditions (May-July precipitation, i.e. months with the maximum accumulation of phytomass) and the deviation from the long-term average values (100%), the observation years were classified into three groups: arid (<100 mm, <70%); medium (100–190 mm, 70– 130%); and wet (>190 mm, >130%). Years with increased moisture are characterized by maximum values of summer and May-summer ombrothermic index; while in the years with poor moisture and relatively low thermic conditions the values are minimal.
In the years with medium moisture conditions, the species richness was particularly high and the species of all biomorphological types were present. This is the most favorable situation for the development of steppe communities. The species diversity of growing vegetative weakly mobile species decreases in the years with dry conditions, while that of vegetative immobile and non-growing species decreases in the years with wet conditions. The years with different moisture conditions also significantly differ in the projective cover of autochthonous assectors (Cleistogenes squarrosa, Agropyron cristatum, Potentilla acaulis) and digressive edifiers (Artemisia frigida). However, the floristic-coenotic core of communities, which ensures their stability, is preserved throughout the entire period of research; it includes 25 perennial species with high constancy in communities.
The structural organization of three-feather formation steppes is reflected in species diversity and phytocoenotic role of particular biomorphological groups of species, and determines the natural potential of steppe ecosystems.

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