As above, so below: Linkages between ground-layer plant communities and subsurface permafrost characteristics in interior Alaska lowlands.

Abstract:

Much of the North American boreal biome is underlain by discontinuous permafrost. Due to polar amplification and rapid warming at northern high latitudes, widespread changes to permafrost are occurring through active layer thickening combined with more localized thermokarst. Both types of permafrost degradation are associated with a loss of key ecosystem services including soil mechanical stability and long-term carbon storage. However, the stability and spatial extent of permafrost varies widely depending on interactions between microclimate, vegetation, and hydrology. Beyond general relationships between permafrost presence or active layer thickness and peat or moss thickness, the linkages between subsurface permafrost characteristics and ground layer vegetation are largely understudied. Here, we use co-associated datasets of ground layer vegetation and permafrost change in interior Alaska to address hypotheses about aboveground-belowground feedbacks in permafrost environments. We surveyed vascular plant, lichen, and bryophyte communities on ten, 400m transects that crossed multiple thaw features in varying stages of thaw progression. Electrical resistivity tomography (ERT) measurements were made to identify subsurface permafrost characteristics up to 20m depth. Geophysical techniques like ERT are a helpful and increasingly common tool for studying aspects of belowground change in permafrost environments, such as identifying ice wedges and mapping the margins of thaw features, but the overarching goal of this project is to investigate new uses of ERT to explore ecological change. Through mixed effects models coupled with indicator species analysis, we found that sites with lower resistivity values at near surface depths were consistently associated with increased graminoid and Sphagnum moss abundance, and decreased abundance of ericoids, lichens, and overall plant species richness. Additionally, the microclimate shifts associated with the observed thaw-driven changeover in plant functional groups may perpetuate more rapid thaw than temperature alone would predict. These linkages between the plant community and subsurface permafrost characteristics can be useful for identifying emerging thaw features, with potential applications in remote sensing and spatial modelling.