Effects of grazing on a salt marsh

Changes in the quantity of plant material in three salt marsh systems: (1) a pristine unaltered marsh, (2) a marsh grazed by ungulates, and (3) a marsh formerly grazed by ungulates, were measured periodically over two years. All three had a mixture of Spartina alterniflora and Salicornia virginica while the latter two also contained Distichlis spicata. The annual production, potential detritus contribution percent dry weight, mineral concentration, plant species composition, and fiddler crab populations were examined for comparative purposes. In addition, the effects of simulated grazing were evaluated at three times of year in a pure stand of S. alterniflora. Finally, an economic assessment and comparison of the three systems was also considered.Living S. alterniflora attained the greatest quantity of standing material in late summer and dead plant material in late winter. Live D. spicata was most plentiful in August and less abundant during February; S. virginica displayed no apparent annual variation in production. Average yearly standing crop increments indicated that the aerial plant production for the ungrazed system (583·4 g/m²/yr) exceeded the production of the formerly grazed marsh (322·3 g/m²/yr). The production of the formerly grazed system exceeded that of the grazed marsh which had an annual production of 221·9 g/m²/yr. Significantly more fiddler crabs were found in the ungrazed area than in the grazed marsh system.