Water-depth and salinity relationships to vegetation dynamics in a Texas coastal marsh: A simulation approach

Distribution of coastal marsh plants has been attributed to varying water depths and salinities. Relationships of water depth and salinity to live, above-ground biomass dynamics of Spartina alterniflora (smooth cordgrass), S. patens (marshhay cordgrass), and Distichlis spicata (saltgrass) were investigated using simulation modelling. Model construction and evaluation were based on published data. Water depth and salinity were responsible for affecting biomass when both values were within tolerance limits for each species. However, low biomass tended to be determined by a single limiting factor when it exceeded a species' tolerance limit. Model results also indicated each species' differential sensitivities to changes in water depth and salinity. Greater temporal variability of these factors may cause shifts of species distributions in Texas.;Field data were collected on San Bernard National Wildlife Refuge (SBNWR), Texas from 1991-1993 to investigate plant-community dynamics. Evaluations of point-intercept transect data revealed a significant (P ;Individual species models were coupled to address community-level dynamics observed at SBNWR. Water-depth and salinity data were incorporated into the model to assess their relative importance to compositional shifts in species. Lower salinities and/or deeper water depths across all zones during this period explained increases in S. alterniflora in the Saline Zone, and S. patens in Brackish and Intermediate Zones. However, observed decreases in D. spicata in the Brackish Zone were not accurately represented in simulations. Factors such as interspecific competition may affect productivity, although this biotic factor was not addressed in the simulation models. Simulations evaluating water depths and salinities representative of drought conditions along the Texas coast demonstrated shifts in species distribution and/or decreases in live, above-ground biomass. Further assessment of responses to Texas coastal marsh conditions will improve model utility in ecological research, management strategies, and restoration projects.