Ecophysiology of northern forests: scaling physiological processes and states in space and time

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Small-scale ecophysiological processes can have large-scale impacts on terrestrial carbon cycling. As a complement to my participation and leadership in the Fluxnet-Canada and Canadian Carbon Program Research Networks, I propose research focused on improving our ability to use measurements of physiological processes and states at the leaf and canopy level to evaluate these processes at larger spatial scales. I propose three complementary areas of study that address some key knowledge gaps in carbon cycle science. (1) We will examine how we might link the dynamic spectral characteristics of boreal forest vegetation to its photosynthetic light use efficiency (LUE). We will add measurements of spectral reflectance and foliar pigments at our Quebec flux sites so as to better understand the contributions of sunlit and shadow canopy fractions to LUE under different levels of stress and stages of phenological development. This could lead to a robust methodology for scaling LUE. (2) We will test different approaches for evaluating forest biomass at large spatial scales using an airborne and a satellite-based lidar and thereby obtain more reliable estimates of aboveground autotrophic respiration for northern ecosystems. We will assess the extent to which different aspects of the sampling (e.g., cover type, slope) drive the variability. We will then use this information to scale the satellite measurements to provincial, national, and circumpolar scales. (3) We will use our flux tower data to evaluate methods for scaling freeze-thaw events and their physiological implications at local to regional scales. We will do this by linking physiological processes and environmental conditions at our flux sites to freeze-thaw data products obtained from a satellite-based microwave sensor. This will allow us to examine how the severity, duration, and distribution of freezing and thawing across a landscape relates to the photosynthetic and respiratory fluxes at our flux sites. It will also allow us to determine how these freeze-thaw dynamics relate to the several thousand square km footprints sampled by the high-precision carbon dioxide concentration measurements we are making as part of the Canadian Carbon Program.