Ditching and Ditch-Plugging in New England Salt Marshes: Effects on Plant Communities and Self-Maintenance

Salt marsh plant communities are regulated by feedback processes involving hydrologic regimes, disturbance, and marsh physical characteristics, and as expected differ among habitat types. Using three barrier beach salt marshes along the Gulf of Maine, we examined the effects of ditching and ditch-plugging on plant characteristics by means of comparisons to natural creek and pool habitats. Results indicated that ditch and creek habitats were similar in terms of species richness and diversity of emergent vascular plants, but cover and biomass were significantly higher in habitat adjacent to creeks. Plant composition in ditch habitat was distinguished by the higher percentage of forb species (associated with poor drainage), while the proportion of tall-form Spartina alterniflora was much higher in creek habitat (associated with sloping banks of creeks). These results are indicative of differences in hydrologic and disturbance regimes that can influence competitive and facilitative interactions, habitat structure, and heterogeneity. Results for pool comparisons indicated that plant characteristics were significantly different between ditch-plug and natural pools. Species richness, diversity, and biomass were significantly lower in ditch-plug habitat compared with all other habitats, and plant cover averaged only 30 % in habitat adjacent to ditch-plugs, which was significantly lower than all other habitats. These differences have ecological implications in terms of habitat structure and function of ditch-plug habitat. In addition, increased stress leading to plant dieback due to ditch-plugging has resulted in subsidence that can decrease the stability of ditch-plug habitat and expedite the loss of salt marsh habitat, especially with rising sea levels.