Controls on carbon exchange in Boreal ecosystems

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A mechanistic understanding of the biophysical controls on carbon exchange necessitates a study of how intra- and inter-annual climate trends affect surface-atmosphere exchanges. The proposed research will quantify the dynamics of net ecosystem exchange of carbon dioxide between a boreal ecosystem and the atmosphere. Tower-based fluxes of CO2 will be continuously measured using micrometeorological methods over a black spruce forest and peatland ecosystem for several years in the eastern James Bay region of the boreal forest. The two field locations are located within several kms of each other and are therefore subjected to the same environmental conditions. Light use efficiency (LUE) will be derived from tower-based measurements of absorbed photosynthetically active radiation and gross ecosystem productivity. The influence of environmental controls on the variation in LUE at each site will be investigated using the set of micrometeorological and biophysical variables. Remotely sensed vegetation indices have been shown to be correlated with LUE at a variety of spatial scales. Upscaling of fluxes will therefore be accomplished using a combination of remote sensing techniques. Tower-mounted radiometers will be used to provide high resolution continuous measurements of vegetation indices. Relationships between vegetation indices and tower-based fluxes will be developed from these field measurements. Ground based algorithms will be applied to comparable satellite-based indices resulting in ecosystem scale estimates of carbon exchange. The research is designed to provide increased knowledge of the critical processes and environmental forcings which drive the atmosphere ecosystem C exchange on time scales ranging from instantaneous, seasonal, annual through inter-annual. Detailed information on ecosystem physiological responses can further be used to modify and validate ecosystem models - becoming tools for studying responses to changing climate.