Asymmetric impacts of surface thaw onset change on seasonal vegetation growth in Arctic permafrost.

Aim: Changes in surface thaw onset in Arctic permafrost can regulate terrestrial ecosystem dynamics. Permafrost surface thaw onset has advanced significantly because of strong Arctic warming. However, surface thaw onset change effects on vegetation during the different growing season stages remain unclear. Location: Arctic and subarctic permafrost region. Time Period: 1982–2016. Major Taxa Studied: Arctic vegetation. Methods: This study investigated surface thaw onset change effects on vegetation growth in the Arctic permafrost region by analysing the relationships between surface thaw onset dates and vegetation indices obtained via satellite remote sensing from 1982 to 2016. Results: The leaf area index (LAI) from April to June was negatively correlated (−0.16 area‐averaged partial correlation coefficient) with surface‐thawed dates in over 78.6% of the Arctic permafrost region, and the LAI from August to October was positively correlated (0.17 area‐averaged partial correlation coefficient) with surface‐thawed dates in over 79.9% of the Arctic permafrost region. These distinct relationships suggest that earlier thaw onset may have a positive effect on vegetation growth during the early stage of the growing season. However, earlier thaw onset can limit vegetation growth during the late stage of the growing season. The different relationships between surface thaw onset and LAI can be explained by moisture availability. This difference occurred because 67.3% of the Arctic permafrost region was more constrained by temperature during the early stage of the growing season, therefore, the earlier thaw onset alleviated this temperature constraint and benefited vegetation growth. During the late stage of the growing season, 47.7% of the Arctic permafrost region was more constrained by moisture. Main Conclusions: Our results suggest that surface thaw onset change effects on vegetation vary by period, and this difference requires careful consideration when predicting ecosystem changes in permafrost regions. [ABSTRACT FROM AUTHOR]