Drivers of Spatial and Temporal Heterogeneity in Vegetation Productivity, Function, and Functional Diversity on the Yamal Peninsula, Siberia, Russia

The understanding of Arctic vegetation patterns and dynamics is necessary to accurately assess carbon gains and ecosystem resistance under projected warming. Uncertainties in determining the relative importance of physical and biological drivers of Arctic vegetation productivity remain, and the potential drivers of vegetation function and functional diversity as determined by Ecosystem Functional Types (EFTs) have not yet been evaluated for the Arctic. This thesis analyzed the climatic, geologic, biologic, and anthropogenic drivers of vegetation productivity, function, and functional diversity across the Yamal Peninsula, a region within the northwestern Siberian tundra, between 2001 and 2018. Productivity was assessed using the Normalized Difference Vegetation Index (NDVI), a proxy for primary productivity and aboveground biomass. Specifically, Max NDVI (representative of peak growing season aboveground biomass) and time-integrated (TI)-NDVI (representative of total growing season productivity) were used. Vegetation function was assessed using NDVI-based EFTs that represent discrete areas with similar carbon gain dynamics, and functional diversity was quantified as EFT richness (the number of unique EFTs within a discrete area).
The spatial distributions of Max NDVI, TI-NDVI, and EFTs were primarily influenced by long-term climate patterns (particularly Summer Warmth Index, the sum of April – September monthly mean temperatures > 0 °C) on the Yamal Peninsula, while spatial patterns of EFT richness were best predicted by the degree of landscape heterogeneity in an area. Max and TI-NDVI increased while EFT richness exhibited no trend across a majority of the Yamal Peninsula between 2001 and 2018, indicating that functional diversity was maintained despite increases in peak aboveground biomass and total productivity. Positive Max NDVI, TI-NDVI, and EFT richness trends were best predicted by distance from the coast, but climate-induced permafrost disturbances, elevation, and human modification were also important predictors of positive trends. Findings indicated that the most extreme warming on the Yamal Peninsula could cause increases in peak aboveground biomass and total productivity but decrease functional diversity. As a whole, this thesis contributes to the knowledge base needed to disentangle the effects of environmental and anthropogenic drivers on Arctic vegetation productivity, function, and functional diversity. Chapter 1 provides insight into the potential future of Arctic regions undergoing warming, moisture regime shifts, and increasing human modification, while Chapter 2 articulates that Arctic regions with heterogeneous landscapes shaped by permafrost disturbance regimes are more likely to experience increases in functional diversity under changing climate conditions.