• What are the primary mechanisms controlling variability in water and carbon fluxes within each of the major boreal ecosystem types?
• What measured modeling parameters are most important in terms of scaling up the seasonal patterns of water and carbon cycling across diverse ecosystem types within the boreal forest region?

• Evaluate the performance of the NASA-CASA (Carnegie-Ames-Stanford Approach) simulation model against water and carbon fluxes measured independently at BOREAS field sites,
• Refine the concepts and algorithms upon which this generalized scheme for soil trace gas emissions can be built, and
• Evaluate requirements to scale-up model results and extrapolate interannual trace gas flux estimates over the entire North America boreal forest region, relying on satellite data to characterize properties of the land surface.

• Model-measurement and model-model discrepancies were observed among all the BOREAS carbon models (with respect to eddy covariance and/or other site measurements), although more detail (physiology, physics) in a subset of models did tend to improve accuracy, as evaluated by RMSE analysis with measured daily CO₂ and ET fluxes.
• The BOREAS carbon models generally predict a small annual net CO₂ sink for the site (1994-1996), whereas the tower data points to a small source (at least more often a small sink). This is explained in part because the models were parameterized for the most productive (well-drained, tall tree) areas around the tower, and consequently their results may have been biased to predict greater production fluxes than typically measured at the NSA-OBS tower (whose footprint also included less productive, wetter areas).
• Model sensitivity comparisons imply that past conditions of the ecosystem (e.g., historical climate patterns and time since last major disturbance), as represented in the models' initial standing wood and soil carbon pools, can be as important as potential future climate changes in predicting the annual model response for a net ecosystem carbon sink in the boreal spruce forest.
• The BOREAS carbon models were observed to have similar responses of higher plant respiration rates and higher ET fluxes in response to prescribed sensitivity increase in air temperature. The models showed different sensitivity responses in their predicted net primary production rates to increased atmospheric CO₂ levels, and in the responses of soil microbial respiration to precipitation inputs and soil wetness. These divergent responses represent some the the largest remaining uncertainties in prediction of future carbon cycling patterns from the boreal forest models.

Potter, C. S., J. Bubier, P. Crill, and P. LaFleur. 2001. Ecosystem modeling of methane and carbon dioxide fluxes for boreal forest sites. Can. J. For. Res. 31: 208-223.

Amthor, J. S., J. M. Chen, J. S. Clein, S. E. Frolking, M. L. Goulden, R. F. Grant, J. S. Kimball, A. W. King, A. D. McGuire, N. T. Nikolov, C. S. Potter, S. Wang, and S. C. Wofsy, Boreal forest CO₂ exchange and evapotranspiration predicted by nine ecosystem process models: Inter-model comparisons and relations to field measurements. J. Geophys. Res., (In Press).