Modelling the response of net primary productivity (NPP) of boreal forest ecosystems to changes in climate and fire disturbance regimes

This study reports on the use of the process-based ecosystem model CENTURY 4.0 to investigate the patterns of net primary productivity (NPP) along a transect across the boreal forests of central Canada and the influence of climate change, CO2 fertilization and changing fire disturbance regimes on changes in NPP over time. Simulated NPP was tested against observed NPP data from northern sites near Thompson (Manitoba) and southern sites near Prince Albert (Saskatcheuan) and shown to be consistent with the data. The temporal dynamics of NPP were very different for the southern, central and northern sites, consistent with the hypothesis that different climate-driven processes regulate forest growth in the various regions of the boreal forest transect case study (BFTCS). The simulations suggest that climate change would result in increased NPP for most sites across the transect. According to the model results, increases in atmospheric CO2 also show increased NPP. The combined influence of climate change and elevated CO2 appear to interact in a positive, but non-linear manner. Statistical analysis of the simulation results indicate that changes in NPP are also positively correlated with changes in net N mineralization (R-2 = 0.89). This supports the conclusion that feedback via N cycling - a coupling of aboveground production with changes in belowground decomposition - is very important for understanding the NPP dynamics of the boreal forest under a changing climate. It was also found that NPP increases with greater fire frequency under current climate conditions, at least over the range of fire return intervals considered (50-200 years). The influence of other changes in disturbance regimes (e.g. altered fire severity and concurrent changes in climate or CO2 fertilization), however, were not considered. (C) 1999 Elsevier Science B.V. All rights reserved.