Published online by Cambridge University Press: 24 August 2009
Between late 1978 and mid-1979, two major coastal vegetation plantings were completed on dredge material in Tampa Bay, Florida. On the dredge material extension of Sunken Island, 1.64 ha of Smooth Cordgrass was planted via 12-cm ‘plugs’ on 1-m centres, in rows 2 m apart. After 14 months, this planting is showing 93.4% survival. On dredge-material island CDA-D, 0.52 ha of mangroves (63% Black and 37% White) was planted via 0.3–1.9 m transplants on 2-m centres. After 13 months, this planting is showing 73.3% survival.
The nature of these two plantings permits a comparison of their cost and man-power requirements. The labour requirements for Smooth Cordgrass were 995 man-hours/ha as opposed to 2,541 man-hours for mangrove transplanting. Smooth Cordgrass requires $4,566/ ha for plugs ($1.03/plug) while mangrove transplants cost $11,459/ha ($3.92/transplant). These costs are for comparison only, as they entail primarily labour and neglect most of the indirect costs that may be experienced.
An analysis of benefits for both salt-marsh and mangrove planting indicates that Smooth Cordgrass provides greater primary production on a g C/m2 basis than mangroves. Both plantings serve as colonial waterbird nesting habitat and source-areas for further planting, but Cordgrass does so in a shorter time-frame. When weighing the positive and negative aspects of both, Spartina alterniflora is preferred over mangroves where both are present.