Simulation of transpiration sensitivity to environmental changes for shrub (Myrica cerifera) thickets on a Virginia barrier island

Shrub (Myrica cerifera) thickets are a major vegetation type on barrier islands. To evaluate the effects of moisture stress on shrub thicket distribution, a water relation model, MCHOG, was developed for Hog Island, a barrier island along the eastern shore of Virginia, USA. The model consists of three submodels: a transpiration submodel based on the Penman-Monteith equation, a rooting-zone water-balance submodel, and water-table dynamics submodel using Darcyʹs law. Precipitation, relative humidity, wind speed, solar radiation, and air temperature data collected on Hog Island in 1991 were used with an hourly time step to simulate transpiration patterns for shrub thickets along a cross-island transect. Transpiration under sufficient soil moisture was defined as potential transpiration. Comparisons were made between the potential transpiration pattern and the transpiration patterns under various environmental change scenarios. Simulation results suggest that the shrub thicket transpiration pattern is sensitive to climate change, landscape change, and sea-level rise. Soil water limits transpiration of all shrub thickets on barrier islands. Elevationally related capillary rise from groundwater also plays an important role in determining shrub distribution patterns. Competition may exist for groundwater resources among individuals of shrub thickets and between shrubs and associated grasses.