Long-Term Growth and Development of Transplants of the Salt-Marsh Grass Spartina alterniflora

The effect of transplant spacings (45, 60, and 90 cm) on establishment of Spartina alterniflora along an eroding shoreline in North Carolina was evaluated and annual biomass production of the planted marsh was compared to a natural marsh. The 45- and 60-cm spacings were more successful for establishment on marginal sites that were near the lower elevation limits of S. alterniflora. The 90-cm spacing was adequate where growing conditions were favorable. Measurements of aboveground growth indicated that there were no differences due to spacing by the end of the second growing season. Differences between spacing treatments in belowground dry weight persisted through three growing seasons. Annual aboveground and belowground standing crop of the transplanted marsh and a nearby natural marsh were compared over a ten-year period. During the early years of development, several characteristics of the transplanted vegetation differed from the natural marsh, but these differences diminished with time. Development of the aerial portion of the transplanted vegetation was rapid, with the most vigorous growth occurring in the second growing season. At that stage of development, the transplants were taller with more flowering stems and a greater standing crop. There were fewer but larger stems than in later years or in the natural marsh. Belowground standing crop increased over the first 3 growing seasons, reached an equilibrium level in 4 growing seasons, and remained constant during the remainder of the study. This indicated that annual production and decomposition of belowground material were about equal. Annual belowground production was estimated to be about 1.1 times the October standing crop of aboveground material. The results indicated that vegetation in a man-initiated S. alterniflora marsh was effective in reducing shoreline erosion and was comparable to a natural marsh growing under similar environmental conditions. The ten-year sampling period was adequate to document that the transplanted marsh was equal in primary productivity and that it was persistent and self-sustaining.