Empirical studies and model simulation of a bottomland hardwood forest dynamics in response to disturbance

Bottomland hardwood forest dynamics on the Patuxent Research Refuge (PRR), Maryland, were examined by (1) a vegetation analysis of forest structural and functional variation; (2) experimental studies of seedling demographic response to white-tailed deer (Odocoileus virginianus) browsing and microhabitat variation; and (3) a model simulation for prediction of deer browsing and flooding effects on succession.;Vertical structure, horizontal pattern, and size distributions of woody species were examined relative to life history strategies and disturbance in the PRR bottomland forest. Forest stands had high structural variation, indicating patchy historical disturbance. No horizontal variation in distribution was apparent, while vertical variation in species abundance, richness, shade tolerance was marked. Dominance of species only marginally adapted to flooding and high regeneration success of late-successional, shade tolerant species suggest the reduction of flooding effects and the importance of species-specific colonization and competition for community organization in the PRR forest.;Tree seedling demography reflected the effects of deer browsing and microhabitat variation in the PRR bottomland forest. Seedling distributions were strongly associated with soil moisture and leaf litter, and selective deer browsing resulted in distinct defoliation patterns and population densities among species. Seedling demography was more sensitive to intensive deer browsing than to microhabitat variation beneath the two dominant canopy tree species (Liriodendron tulipifera and Fagus grandifolia). Deer browsing significantly reduced seedling recruitment, basal diameter increment, rate of population increase, and survival rate at the community level. At the population level deer browsing effect was less apparent because of interaction with life history strategies of species and environmental variation.;Long-term deer browsing and flooding effects on forest succession were simulated with a forest gap model, ZELIG. The model was modified, based on empirical data from this and other published studies, to emphasize seedling dynamics. The model predicted significant effects of deer browsing and periodic flooding on population size distributions, relative species dominance, and biomass production. Impacts at the population, community, and ecosystem scales were sensitive to the frequency and intensity of disturbance and forest succession, suggesting that multiple levels of forest attributes may need to be evaluated simultaneously for prediction of bottomland forest dynamics.