Sensitivity of Phytoproduction in Low-Mountain Steppe Landscapes in the Southern Urals to Hydrothermal Fluctuations

Identification of the natural range and sequence of landscape states is required to assess the response of the phytoproduction process to external signals in terms of inertia and susceptibility. We studied the spatio-temoral dynamics of normalized difference vegetation indices (NDVI) in the steppe landscape of the Orenburgsky Reserve to rank groups of natural units by the sensitivity of functioning to hydrothermal fluctuations and climatic trends. Data for the vegetation period of 2013-2024 for 82 periods were taken. We performed the principal component analysis to identify 5 factors describing either the NDVI dynamics for a particular part of the vegetation period or the specific response of units to extreme weather events. Eight classes of annual variation were identified, differing in the time of reaching the peak of phytomass and the severity of its late summer decrease. We found evidence for the synchronicity of intraseasonal changes in average NDVI between groups of units. Various forms of resistance to hydrothermal fluctuations were distinguished. Xeropetrophytic and dry steppes on ridges and slopes are the most resistant to summer drought almost not losing phytomass. However, they are susceptible to heavy precipitation in the late summer and increase phytomass. In case of climate warming and drying, they will be the most resistant. Typical steppes on the plateau on loamy southern chernozems are more susceptible to late summer extreme precipitation, provided that the first half of summer was wet. Xeromesophytic and mesophytic communities in gullies lose phytomass most strongly during summer drought being almost not susceptible to additional moisture. This makes them the most vulnerable in case of increase in temperature and decrease in precipitation.