Permafrost Degradation and Vegetation Growth Beyond the Polar Circle in Siberia

Permafrost thawing is potentially a crucial but poorly investigated factor that influences vegetation dynamics in the Arctic. We studied the permafrost thaw rate beyond the Polar Circle in Siberia. We analyzed its influence on the larch (Larix spp.) growth and Arctic vegetation (sparse larch forests, tundra, and forest–tundra communities) productivity (NPP). We checked the following hypotheses: (1) satellite gravimetry is valid for permafrost thawing analysis; (2) meltwater runoff stimulated trees’ growth and NPP. We used satellite (GRACE, Terra/MODIS) and field data, and larch tree radial growth index measurements. We found a continuous negative trend in the terrestrial water content (r2 = 0.67) caused by permafrost thawing beyond the Polar Circle. Runoff is maximal in West and Mid Siberia (9.7 ± 2.9 kg/m2/y) and decreases in the eastward direction with minimal values in the Chukotka Peninsula sector (−2.9 ± 3.2 kg/m2/y). We found that the growth increment of larch trees positively correlated with meltwater runoff (0.5…0.6), whereas the correlation with soil water content was negative (−0.55…−0.85). Permafrost thawing leads to an increase in the Arctic vegetation productivity. We found a positive trend in NPP throughout the Siberian Arctic (r2 = 0.30). NPP negatively correlated with soil water content (r = −0.55) and positively with meltwater runoff (West Siberia, r = 0.7). An increase in VPD (vapor pressure deficit) and air and soil temperatures stimulated the larch growth and vegetation NPP (r = 0.5…0.9 and r = 0.6…0.9, respectively). Generally, permafrost degradation leads to improved hydrothermal conditions for trees and vegetation growth and contributes to the preservation of the Arctic as a carbon sink despite the increase in burning rate.