| Summary: | This dissertation focuses on improving knowledge of decade-time scale plant community change and its impact on ecosystem function (i.e. biogeochemical cycling, and energy balance) in select sites throughout the North American Arctic. The studies presented largely take advantage of historic research activities conducted between the late 1950's and mid-1970s that have been resampled to assess change in ecosystem structure (i.e. makeup of plant species and abundance) and ecosystem function. The overarching goal of this dissertation is to determine how ecosystem function has changed in central Baffin Island, Canada, and in northern Alaska near Barrow in response to changes in climate, herbivory, nutrient availability, and plant community change over the past 30-60 years. At two sites, Baffin Island Canada, and Barrow Alaska, we used newly developed multivariate-geostatistical analytical procedure to assess change in ecosystem function over time. At our site in central Baffin Island, the greatest change in ecosystem function was noted for plant communities with high soil moisture. For example, two pond margin communities: Campylium-Aulacomnium-moss meadows and Eriophorum-Pleuropogon wetlands increased in biomass by 178% and 46%, while NDVI increased 35% and 16%, respectively. Soil moisture was found to decrease in Carex stans wet meadows and Campylium-Aulacomnium-moss meadows by 30% and 24%, respectively. Other changes were heterogeneous and largely plant community specific. Similarly, in Barrow Alaska, the greatest change in ecosystem function was found for aquatic and wet plant communities, where productivity varied and soil moisture increased along with methane flux over time. Interestingly, our functional models appeared to be responsive to years with high lemming populations, which were found to decrease albedo and NDVI, while increasing methane fluxes for both aquatic Carex graminoid and wet graminoid tundra. Further, moist and dry communities which decreased in soil moisture between 1972-2010 appeared more ...
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