Vegetation response to disturbance in a coastal marsh in Texas

Disturbance is considered one of the main factors influencing plant species composition and diversity. We conducted a field study to address the plant community response in a coastal marsh to a major disturbance. In 1992, muskrats (Ondatra zibethicus L.) completely removed vegetation within a 450 ha area of intermediate coastal marsh in Texas, USA. We used vegetation data collected prior to the disturbance (1989-1991) as a baseline for comparison to that recorded annually for a decade (1992-2002) following the disturbance. We compared species diversity, richness, relative abundance, evenness, and species similarity between pre and postdisturbance periods to evaluate the temporal response of the disturbed plant community. Plant diversity in the study area returned to predisturbance levels after 10 years. Species diversity in the study area had two peaks following the main disturbance. These peaks are associated with fluctuations of the water levels in the area. Our results suggest that it is possible to control the sedge or grass dominance in a community by subjecting the area to a carefully timed willful disturbance (e.g., grazing or fluctuating water levels) to achieve management goals. However, vegetation composition in the area changed from a grass-dominated (predisturbance) to sedge-dominated (postdisturbance) community. At the conclusion of sampling in 2002, plant species abundance, evenness, dominance, and richness conditions reached levels similar to predisturbance. However, the species composition after a decade postdisturbance differed from that during the predisturbance period. Therefore, even though we are able to predict the return of species diversity, evenness, and richness of a community after a period following disturbance, the actual species composition of an intermediate marsh following recovery is difficult to determine accurately, as it is contingent on several biotic and abiotic conditions that prevail while the system recovers from disturbance.