A SPATIAL PATCH DYNAMIC MODELING APPROACH TO PATTERN AND PROCESS IN AN ANNUAL GRASSLAND

Landscapes are hierarchical mosaics of patches that differ in their ag e, size, shape, content, and other aspects. The Jasper Ridge serpentin e grassland exemplifies hierarchical patchiness and pattern-process in teractions that are common features of natural ecosystems. Gopher moun ds formed each year destroy all the plant individuals underneath and r esult in conspicuous spatial pattern in the landscape. A snapshot of t he system is, therefore, a reflection of the patch mosaic of gopher mo unds that are different in age and species composition and abundance. Based on a patch dynamics perspective, we have developed a spatially e xplicit patch-based modeling approach to studying landscape pattern an d process dynamics. The simulation model (PATCHMOD) has two major comp onents: a spatially explicit, age- and size-structured patch demograph ic model and a multiple-species plant population dynamic model. We use this simulation model to examine the spatiotemporal dynamics of the d isturbance patches and of populations of two species on the local and landscape scales. The spatial patch dynamic model can relate spatiotem poral dynamics of plant populations to the age- and size-structured di sturbance patch population, taking into account variability in microha bitats, complexity in patch overlap, and patch-based plant competition . The localized gopher disturbances can significantly structure the ve getation dynamics at the landscape level. Local populations at the pat ch level may go extinct frequently, though metapopulations may show li ttle fluctuation. Disturbance promotes coexistence of Bromus mollis an d Lasthenia californica by divorcing local competitive exclusion and g lobal extinction. The functional representation of an ecological relat ionship such as density-dependent fecundity at the local patch scale m ay be transmuted by patchiness at the landscape scale.