The Stability of Phytomass Dynamics in the Nature Reserve and Pasture Low-Mountain–Steppe Landscapes of the Southern Urals

摘要

Abstract In the steppe zone, high sensitivity of a vegetation cover to contrasts of moistening raises the question about the dependence of intra-seasonal dynamics of phytomass on the vegetation cover structure and the land topography. Based on the example of the Aituar steppe (Orenburg oblast), the hypothesis about the nonequivalence of spatial factors of variability of functioning is tested under conditions of a nature reserve regime and with a pasture load. A measure of instability of the types of green phytomass dynamics (Shannon’s index) is calculated by the recurrent five gradations of deviations of intraseasonal increments of NDVI vegetation index from the mean values. A correlation between the types of dynamics and the types of tracts determined by belonging to the landforms with characteristic types of phytocenoses has been established. The zones of the most unstable phytoproduction functioning are typical of ravines with meadow steppes. The nature reserve regime makes the phytomass dynamics stable due to the stronger governance by climate processes of a landscape scale. In the grazed plots, frequent changes of the variants of phytomass increments are more typical and the dependence on the local factors, such as rockiness and groundwater level, intensifies. In the pasture plot, in some places the dynamics with an intense late-spring accumulation of phytomass and a small decrease or resumption by the end of summer due to the growing share of ungrazed and grazing-resistant species becomes dominant.