Influence of the Tussock Growth Form on Arctic Ecosystem Carbon Stocks

Abstract:

The influence of plant growth forms on ecosystem carbon (C) cycling has been under appreciated. In arctic tundra, environmental factors and plant traits of the sedge Eriophorum vaginatum cause the formation of mounds that are dense amalgamations of belowground C called tussocks. Tussocks have important implications for arctic ecosystem biogeochemistry and C stocks, but the environmental and biological factors controlling their size and distribution across the landscape are poorly understood. In order to better understand how landscape variation in tussock size and density impact ecosystem C stocks, we formed the Carbon in Arctic Tussock Tundra (CATT) network and recruited an international team to sample locations across the arctic. The CATT network provided a latitudinal and longitudinal gradient along which to improve our understanding of tussocks’ influence on ecosystem structure and function. CATT data revealed important insights into tussock formation across the arctic. Tussock density generally declined with latitude, and tussock size exhibited substantial variation across sites. The relationship between height and diameter was similar across CATT sites indicating that both biological and environmental factors control tussock formation. At some sites, C in tussocks comprised a substantial percentage of ecosystem C stocks that may be vulnerable to climate change. It is concluded that the loss of this growth form would offset C gains from projected plant functional shifts from graminoid to shrub tundra. This work highlights the role of plant growth forms on the magnitude and retention of ecosystem C stocks.