Satellite Gravimetry in Studies of Permafrost Thawing and Vegetation Productivity in the Cryolithozone

Abstract Changes in the hydrothermal regime of soils caused by the melting of the permafrost layer are the most important ecological factor in the dynamics of vegetation in the cryolithozone. The impact of soil thawing on the growth index (GI) of larch ( Larix spp.) and on the gross and net primary productivity (GPP and NPP) of vegetation in the Arctic region of Central Siberia (sparse forests, tundra, and forest tundra) is investigated. The following hypotheses are tested: (1) gravimetric data allow us to assess the dynamics of water mass in soils; (2) thawing of frozen soils stimulates the growth of woody plants and the productivity of vegetation. This work uses methods of dendrochronology, field data, satellite gravimetry (GRACE survey), and remote sensing of GPP (Terra/MODIS survey). An analysis of gravimetric data has revealed a significant long-term trend of decreasing water mass in soils of the cryolithozone ( R 2 = 0.68). The amount of water released during melting is estimated at 6.4 ± 2.3 kg/m –2 per year. A close relationship was established between the GI of larch and GPP with moisture anomalies in soils ( r = –0.7 and r = –0.9, respectively). The increasing temperature of the root zone and the deficit of water vapor moisture also have a positive effect on the GI of larch and the GPP value of vegetation as a whole ( r = 0.6 and r = 0.6–0.9, respectively). It is established that pyrogenic carbon losses are significantly (two orders of magnitude) lower than the NPP value. Under conditions of waterlogged soils, which are typical for the Arctic, climate warming is accompanied by an improvement in the hydrothermal growth regime of the plant cover and contributes to an increase in the productivity of vegetation and the preservation of the cryolithozone status of a carbon sink area.