A mathematical simulation model of ecosystem response to natural stresses

A mathematical model is presented which simulates structural and functional relationships in an annual herb ecosystem characteristic of the granitic outcrops of the Southeastern Piedmont. The model simulates ecological responses to environmental stresses, primarily in terms of demographic changes in dominant plant species and alterations in ecosystem processes such as nutrient cycling.

Previous experimental research on these ecosystems, and the ecological significance of environmental stress are reviewed in detail. Nutrient cycles are depicted deterministically, water cycles are stochastic, and simulated productivity is a product of the two.

The model itself is written in Fortran-10, and is easily adapted to most fortran utilities. Equations are written in linear difference as opposed to integrated differential form. For this reason, the model is constructed in an extended rather than subprogram form. All 2190 "day" steps of the model occur within a single, major loop. While only five years of daily estimated data are possible as output in the extended mode, the annual cycles of the biota are well represented in this time frame. Stress implementation is achieved through manipulation of simulated rainfall and soil depth constants.

Heuristic value of this model and others is developed, and further studies are suggested.