|
|
|
|
|
|
|
(Ecological Modeling 101:61-78) |
|
||||
|
John D. Aber and Scott V. Ollinger Complex Systems Research Center, University of New Hampshire, Durham, NH 03824
Charles T. Driscoll
|
|||||
A generalized, lumped-parameter model of carbon (C), water, and Nitrogen (N) interactions in forest ecosystems (PnET-CN) is presented. The model operates at a monthly time step and at the stand-to-watershed scale, and is validated against data on annual net primary productivity, monthly carbon and water balances, annual net N mineralization, nitrification, foliar N concentration and annual and monthly N leaching losses for two sites: Hubbard Brook (West Thornton, NH) and Harvard Forest (Petersham, MA). It is then used to predict transient responses in function resulting from changes in land use and N deposition, as well as the maximum rate of N cycling which can be sustained for any given combination of site, climate and species. Model predictions suggest a very long legacy effect of land use history on N cycling. Even with only one "active" soil organic matter pool, complete recovery from three modest harvests at Hubbard Brook is predicted to require more than two centuries at current N deposition rates. Complete recovery is predicted to take even longer at the Harvard Forest where biomass removals have been more intense. PnET-CN is used to predict maximum sustainable rates of N cycling for 14 sites throughout the northeastern U.S. Predicted maximum values were higher, as expected, than measured N mineralization rates for all but one site. The measured fraction of N mineralization nitrified at these 14 sites showed a general relationship with the ratio of measured to maximum net N mineralization. This latter ratio is discussed as a potentially useful indicator of the degree of nitrogen saturation in forest ecosystems. A regional map of predicted maximum N cycling rates is presented based on regressions between model predictions and summary climatic variables. |
|||||
