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Modeling Studies for BOREAS
NASA-CASA Prediction for Northern Study Area Carbon Cycles
BOREAS Carbon Flux Plots
Top: Predicted net ecosystem exchange (NEP) of carbon (black line) and average daily NEP fluxes measured by TF-3 in 1994 (OBS; triangle) and by TGB-3 in 1996 (Fen; filled square-hollow, open square-hummock). The midnight to midnight average of NEP at the OBS site was computed for days during which no fewer than 44 half-hourly CO2 flux measurement data points (i.e., >90%) were recorded.
Bottom: Predicted net primary production (NPP) for the respective sites and years (black line-overstory, gray line-moss ground cover).
NASA-CASA Prediction for Annual NEP BOREAS Regional Area
BOREAS Regional Flux Conditions
Main Conclusions from BOREAS Follow-on Carbon Modeling Comparisons (NSA - Old Black Spruce Tower Site)
  • 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.
 

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