© 2000 Heron Publishing—Victoria, Canada
Regional assessment of boreal forest productivity using an ecological process model and remote sensing parameter maps
J. S. Kimball (1, 3), A. R. Keyser (1), S. W. Running (1) and S. S. Saatchi (2)
1. Numerical Terradynamic Simulation Group, School of Forestry, University of Montana, Missoula, MT 59812, USA / 2. NASA Jet Propulsion Laboratory, Pasadena, CA 91109, USA / 3. Flathead Lake Biological Station, University of Montana, 311 Bio Station Lane, Polson, MT 59860-9659, USA / Received June 3, 1999
Summary
An ecological process model (BIOME-BGC) was used to assess boreal forest regional net primary production (NPP) and response
to short-term, year-to-year weather fluctuations based on spatially explicit, land cover and biomass maps derived by radar
remote sensing, as well as soil, terrain and daily weather information. Simulations were conducted at a 30-m spatial resolution,
over a 1205 km2 portion of the BOREAS Southern Study Area of central Saskatchewan, Canada, over a 3-year period (1994–1996). Simulations
of NPP for 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 area, whereas biophysical differences between broadleaf deciduous and evergreen coniferous
vegetation were of secondary importance. Simulations of NPP were strongly sensitive to year-to-year variations in seasonal
weather patterns, which influenced the timing of spring thaw and deciduous bud-burst. Reductions in annual NPP of approximately
17 and 22% for 1995 and 1996, respectively, 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 the importance of sub-grid
scale land cover complexity in controlling boreal forest regional productivity, the dynamic response of the biome to short-term
interannual climate variations, and the potential implications of climate change and other large-scale disturbances.
Keywords:
BIOME-BGC, BOREAS, carbon cycle, ecosystem modeling, net primary production, NPP, radar, SAR.
