© 1991 Heron Publishing—Victoria, Canada
Considerations in modeling change in temperate forest nitrogen cycles
R. J. Raison (1) and R. Stottlemyer (2)
1. Division of Forestry, CSIRO, P.O. Box 4008, Canberra, ACT 2600, Australia / 2. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, 240 West Prospect Road, Fort Collins, CO 80526, USA /
Summary
The general features of nitrogen (N) cycles in temperate forests and the important processes to consider when modeling change
in these cycles include atmospheric inputs, N fixation, litter (root and aboveground) transfers and decomposition, soil processes,
N uptake and effects on productivity and litter quality, and N outputs. Nitrogen cycling is closely linked with the carbon
(C) and water cycles. Thus models of N cycling must include aspects of these other cycles. Although much is known about individual
processes, development of a generic model of forest N cycling is not possible at present because the links and interactions
among the individual processes are not well understood.
The weakest links with respect to the N cycle are: quantification of atmospheric (especially dry) deposition rates in polluted
environments, controls on C and N allocation in vegetation, controls on N turnover in fine roots, controls on decomposition
of the older components of soil organic matter, and feedbacks among N availability, litter “quality” and subsequent N mineralization
rates.
To examine possible effects of long-term change in climate or atmospheric chemistry on the storage of C and other elements
in forest ecosystems, we need to model in detail the effects of these factors on complex soil processes such as organic matter
decomposition. Some promising models have been developed, but they need to be validated across a range of forest types before
they can be used with confidence for long-term prediction. Mean annual leaf litter N concentration offers potential as a simple
index of annual N uptake in forests.
