Regional assessment of boreal forest productivity using an ecological process model and remote sensing parameter maps

An ecological process model (BIOME-BGC) was used to assess boreal forest re gional net primary production (NPP) and response to short-term, year-to-yea r weather fluctuations based on spatially explicit, land cover and biomass maps derived by radar remote sensing, as well as soil, terrain and daily we ather information. Simulations were conducted at a 30-m spatial resolution, over a 1205 km(2) portion of the BOREAS Southern Study Area of central Sas katchewan, Canada, over a 3-year period ( 1994-1996). Simulations of NPP fo r the study region were spatially and temporally complex, averaging 2.2 (+/ - 0.6), 1.8 (+/- 0.5) and 1.7 (+/- 0.5) Mg C ha(-1) year(-1) for 1994, 1995 and 1996, respectively. Spatial variability of NPP was strongly controlled by the amount of aboveground biomass, particularly photosynthetic leaf are a, whereas biophysical differences between broadleaf deciduous and evergree n coniferous vegetation were of secondary importance. Simulations of NPP we re strongly sensitive to year-to-year variations in seasonal weather patter ns, which influenced the timing of spring thaw and deciduous bud-burst. Red uctions in annual NPP of approximately 17 and 22% for 1995 and 1996, respec tively, were attributed to 3- and 5-week delays in spring thaw relative to 1994. Boreal forest stands with greater proportions of deciduous vegetation were more sensitive to the timing of spring thaw than evergreen coniferous stands. Similar relationships were found by comparing simulated snow depth records with 10-year records of aboveground NPP measurements obtained from biomass harvest plots within the BOREAS region. These results highlight th e importance of sub-grid scale land cover complexity in controlling boreal forest regional productivity, the dynamic response of the biome to short-te rm interannual climate variations, and the potential implications of climat e change and other large-scale disturbances.