A simulation model of the impacts of green-tree reservoir management on bottomland hardwood seedling growth and survival

Abstract

Green-tree reservoirs are stands of bottomland hardwoods that are impounded with levees, equipped with water control structures, and flooded during the fall and winter to provide mast and invertebrates for waterfowl. We developed a model to evaluate the potential impacts of green-tree reservoir management on seedling growth and survival of three bottomland hardwood species (overcup oak, water elm, and willow oak). The model is a compartment model based on difference equations with a time step of 6 months and operates on a microcomputer. Each species is represented by two series of 10 state variables representing the number and height of seedlings, respectively, in age-classes from 1 to 10 yr. Seedling growth is a function of the length of flooding during the growing season and light availability; seedling survival is a function of these 2 parameters as well as the depth of flooding during the dormant-season. The model ordinates the relative growth rates of the three species accurately based upon flood tolerances described in the literature. Simulations indicate that changes in the length of flooding during the growing season, flood depth during the dormant season, and light availability influence both the composition and abundance of regeneration of bottomland hardwood species. Regeneration of all species was reduced as either the length of flooding during the growing season, light availability, or dormant season flood depth approached an extreme for that species, regardless of the values of the other environmental gradients. Our model, with slight modifications, could be incorporated into existing bottomland hardwood simulation models that do not specifically represent seedling growth and survival.