The influence of duration-of-inundation on development of a man-initiated Spartina alterniflora Loisel. Marsh in north carolina

The relative growth responses of a man-initiated Spartina altemiflora Loisel. marsh were monitored annually in four duration-of-inundation zones (4, 7, 9, and 11 h daily) during a 4-yr period following the 17-month establishment period, with another sampling 10 yr later. There was a general trend of maximum values for height, number of flowers · m −2, basal area, and aboveground standing crop to occur in the 7-h inundation zone and for these values to decrease in the 9- and 11-h zones at the end of the second growing season (17 months after planting). This trend was reversed from the third through the fifth growing seasons with height, number of flowers · m −2, and aboveground standing crop significantly higher in the longest (11-h) inundation zone. Although other angiosperms began invading the upper elevation, lesser inundated zones during the second growing season, populations were too small to sample until the following growing season (29 months after planting), when they constituted ≈40% of the aboveground standing crop in the uppermost (4-h) zone. The aboveground standing crop of the S. alterniflora-dommated 11-h inundation zone became stabilized by the third growing season, but the belowground material dry weight continued to increase in all zones through the fifth season when its rate of accumulation began to stabilize in the lowermost zones. Although the uppermost zone was dominated by Phragmites communis Trin. by the twelfth season, Spartina alterniflora dominated the other zones where it constituted more than three-fourths of the aboveground standing crop and had spread ≈ 30 m beyond the planting toward the open water of the estuary. The number of invading species present in the fifth season decreased by > 65% in the twelfth season, but the remaining invaders generally constituted relatively more of the aboveground standing crop by the twelfth season. Over the 12 seasons the experimental S. alterniflora planting developed into a marsh with the species composition dictated by the availability of disseminules of other angiosperms under the prevailing environmental conditions of duration-of-inundation and salinity.