Ecohydrological feedbacks between permafrost and vegetation dynamics

Abstract

The presence of forest vegetation can aid in preserving the permafrost layer by maintaining lower soil temperatures via the accretion of an organic layer at the surface. This layer has a low bulk density and low thermal conductivity (due also to high evapotranspiration rates by forest vegetation), which insulates ice-rich permafrost. Forest removal can lead to significant increases in the summer soil temperature, which increases the thickness of the active layer (i.e., the surficial layer above permafrost which thaws during summer and freezes again in winter) and causes a rise in the active layer towards the surface. When vegetation is sensitive to saturated soil conditions, a rise in the active layer can lead to the conversion of forested areas to wetlands. In this manuscript, we develop a modeling framework to relate vegetation–permafrost feedbacks to the emergence of multiple stable ecosystem states. Factors related to soil temperature and hydrologic characteristics of the system were examined to see how they affect the location of the stable and unstable states. This model was also used to examine how an increase in precipitation would affect the temporal dynamics of the active layer and vegetation. Results show that the presence of forest vegetation can enhance the resilience of the system in that it is less prone to state shifts following a disturbance. Understanding these dynamics is important given, (i) the rapid rate at which these systems can shift between states, (ii) the projected climatic changes for forested areas underlain by permafrost and (iii) the high rates of forest loss in these areas.