Modeling landscape net ecosystem productivity (LandNEP) under alternative management regimes

Forests have been considered as a major carbon sink within the global carbon budget. However, a fragmented forest landscape varies significantly in its composition and age structure, and the amount of carbon sequestered at this level remains generally unknown to the scientific community. More precisely, the temporal dynamics and spatial distribution of net ecosystem productivity (NEP) in a mosaic are dependent on ecosystem type and the chronosequence of the ecosystem in the landscape. In this study, we developed a model, LandNEP, to follow the change in NEP by ecosystem and chronosequence. The model creates user-defined hypothetical landscape mosaics of ecosystem and age over a given number of simulation years. It then calculates NEP and biomass for each ecosystem and over the entire landscape based on a distribution function, and any disturbances that have occurred within a landscape at a given year. We simulated three different scenarios and a sensitivity analysis within a hypothetical landscape. Based on these scenarios, we were able to show that theoretically, timber harvest strategies requiring rotations that go beyond the time of an ecosystem's maximum NEP will ultimately yield the greatest cumulative NEP value. Furthermore, the sensitivity analysis demonstrated that increasing the disturbance interval could switch an ecosystem from acting as a net carbon source to acting as a net carbon sink. These results suggest that carbon losses within a managed forested landscape could be mitigated by permitting the ecosystem to reach its maximum as a net carbon sink before harvesting timber. Therefore, alternative management regimes play a leading role in determining to what extent a landscape sequesters carbon. (C) 2002 Elsevier Science B.V. All rights reserved.