Arctic tundra ecosystems and their effects in a changing climate

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The Canadian Arctic contains about one-third of all circumpolar tundra and this land has particular cultural, biophysical and economic significance for all Canadians, especially its northern residents. However, global warming in the Arctic is occurring at an unprecedented rate and is driving significant changes in terrestrial and oceanic systems, such that feedbacks amplifying the warming are inevitable. On the Arctic tundra the alteration of vegetation communities and consequently their interactions with the atmosphere will play a significant role in future warming. Hence, we need to improve our understanding of these ecosystems and their role in the climate system. The goal of this research program is to examine how composition and structure of Arctic vegetation influences the exchanges of energy, water and trace gases so as to improve model predictions of future Arctic conditions. The proposed research will continued our long-term study of tundra-atmosphere interaction in the Canadian low-Arctic near Daring Lake, NWT, where we have instrumented 4 different ecosystems (heath, dwarf-shrub, low-shrub and fen) for measurements of ecosystem-scale energy, water and carbon fluxes. The existing measurement records vary from 5-13 years. The data will be used to answer several critical research questions. First, we will examine how intra-season and inter-annual variation in these fluxes respond to variations in climate at different time scales (weeks to seasons) and to develop knowledge of how different tundra types respond either similarly or differently to climate. Second, we will focus our efforts on tundra water use efficiency (WUE). This important parameter links carbon dioxide and water vapour fluxes and is critically important to understanding ecosystem-atmosphere feedbacks, especially under a regime of shifting vegetation. We will study WUE of tundra by using our whole-ecosystem measurements of water vapour and CO2 fluxes from the different tundra types, field experiments to partition the water flux into canopy and under-canopy components, and employ a sophisticated ecosystem process model to investigate the impact of vegetation changes on WUE. The third prong of this research program is to use our measurements and knowledge to assist in improving the representation of tundra vegetation (especially shrubs) in the land surface scheme of Environment Canada's Canadian Earth System Model. This research will aid in better predictions of future climate states in the Arctic, its response to global warming and increase the scientific understanding of how sensitive Arctic ecosystems are to climate change. It will inform policy makes about the importance of Arctic ecosystems and changes that we can expect to encounter in the future, which will provide a framework for improving climate change adaption strategies for northern inhabitants and their communities.