Climatic Changes as Factors of Transformation in Green Phytomass Stocks of the Arctic Islands Reindeer Pastures

Using data from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite (MOD13Q1 product) over the period of 2000–2022, changes in the aboveground biomass of tundra phytocenoses on the archipelago of the Novosibirsk Islands have been analyzed. The observation period coincides with the onset of the formation and development of the rising phase of near-surface air temperature (SAT). According to instrumental measurements at the meteorological station on Kotelny Island, the average annual SAT value changed from –17.4°C in 1979 to –9.9°C in 2020. The increase in average annual SAT values is largely due to the transformation of negative air temperatures. The dynamics of green phytomass productivity between years on the islands of the archipelago are clearly demonstrated by the increase in the Enhanced Vegetation Index (EVI), and the changes are visualized by the index Integral Vegetation Condition Index (IVCI). Observations began with a predominance of the lowest values (2000–2002); subsequently, a gradual increase in values and the amplitude of their fluctuations was recorded, with an increase in the proportion of more productive communities (2003–2017). The overall trend of changes is towards an increase in the EVI index and a transition to a region of stable values significantly exceeding the average (a period of 2018–2022). A previously developed model for calculating the green fodder stock based on spectral values made it possible to identify the distribution patterns of aboveground phytomass on the islands of the archipelago and their changes for the entire observation period. For 2000–2021, a general increase in gross aboveground phytomass was noted on the islands. Maximal stock values were recorded in the plant communities of the southernmost island, Bolshoi Lyakhovskii: an increase from 5.0–6.0 to 8.0–9.0 c/ha. The average stock of green phytomass over the considered period for the entire archipelago increased in the range from 1.23 (Stolbovoi Island) to 2.06 times (Novaya Sibir Island). Changes in green forage reserves may be important for regulating the abundance and composition of the region’s animal population, forming seasonal migration patterns of wild reindeer, and the rate of accumulation and migration of elements in trophic chains.