Vegetation grows more luxuriantly in Arctic permafrost drained lake basins

As Arctic warming, permafrost thawing, and thermokarst development intensify, increasing evidence suggests that the frequency and magnitude of thermokarst lake drainage events are increasing. Presently, we lack a quantitative understanding of vegetation dynamics in drained lake basins, which is necessary to assess the extent to which plant growth in thawing ecosystems will offset the carbon released from permafrost. In this study, continuous satellite observations were used to detect thermokarst lake drainage events in northern Alaska over the past 20 years, and an advanced temporal segmentation and change detection algorithm allowed us to determine the year of drainage for each lake. Quantitative analysis showed that the greenness (normalized difference vegetation index [NDVI]) of tundra vegetation growing on wet and nutrient-rich lake sediments increased approximately 10 times faster than that of the peripheral vegetation. It takes approximately 5 years (4-6 years for the 25%-75% range) for the drainage lake area to reach the greenness level of the peripheral vegetation. Eventually, the NDVI values of the drained lake basins were 0.15 (or 25%) higher than those of the surrounding areas. In addition, we found less lush vegetation in the floodplain drained lake basins, possibly due to water logging. We further explored the key environmental drivers affecting vegetation dynamics in and around the drained lake basins. The results showed that our multivariate regression model well simulated the growth dynamics of the drainage lake ecosystem (Radj2=.73, p < .001) and peripheral vegetation (Radj2=.68, p < .001). Among climate variables, moisture variables were more influential than temperature variables, indicating that vegetation growth in this area is susceptible to water stress. Our study provides valuable information for better modeling of vegetation dynamics in thermokarst lake areas and provides new insights into Arctic greening and carbon balance studies as thermokarst lake drainage intensifies.

Automated summary

This study utilized satellite observations to detect thermokarst lake drainage events in northern Alaska over the past 20 years, finding that tundra vegetation growing on lake sediments showed significantly faster greenness growth compared to peripheral vegetation, with drained lake basins having NDVI values approximately 0.15 higher than surrounding areas. Less lush vegetation was observed in floodplain drained lake basins, possibly due to water logging. Among climate variables, moisture variables were more influential than temperature variables, indicating vegetation growth in this area is susceptible to water stress.