Biophysical Regulation of Energy Budget in Disturbed Forest Ecosystems of a Northern Wisconsin Landscape

Energy balance and partitioning are critical for understanding other ecosystem processes such as net carbon exchange and evapotranspiration. As a research component of a large effort for exploring the cumulative exchanges of CO2, H2O, and energy at the landscape level (i.e., across multiple ecosystems), this study is designed to: (1) examine the energy balance of dominant ecosystems including net radiation (Rn), latent heat (LE), sensible heat (H), soil heat flux (G), and heat storage (M) within the canopy column; (2) explore the variations of each energy balance term among ecosystems and their dynamics from hourly to yearly time steps; and (3) explore the vegetation and microclimatic regulations of energy partitioning. Our field data were collected from 8 eddy-covariance flux towers, 14 microclimatic stations, 105 ground measurements of vegetation (LAI, age, DBH, density, height, and canopy roughness), and 21 soil temperature profiles across the landscape in the Chequamegon National Forest of northern Wisconsin. Regression and ANOVA analyses were used to explore the changes of energy budget and its components with vegetation and climatic variations. Overall, we found 65-85% energy enclosure for all 8 ecosystems. Significant variation in partitioning energy budget existed among ecosystems and, more importantly, partitioning of energy budget depended on vegetation characteristics such as LAI, age, canopy openness, and tree height. Energy enclosure decreased linearly with vegetation height. Across temporal scale, changes in each energy term and energy balance closure depended on weather conditions (e.g. cloudiness) and vegetation characteristics.