Depending on the species composition of the forest and degree of damage, total dead biomass per hectare may exceed 150 metric tons, including 0.57 metric tons of nitrogen and 0.18 metric tons of phosphorus. The influence of the release of these nutrients on nearshore systems could be substantial. The material is in pools that decompose at vastly different rates, with leaves being fastest, large woody material slowest, and roots intermediate.

Immediately before Hurricane Andrew, we had discovered the remains of tree trunks that had been blown down by Hurricane Donna in 1960. This finding indicates that mangrove wood is extremely persistent. Robertson and Daniel (1989) reported that decomposing mangrove wood was a sink for nitrogen. Within the first few months after decomposition began, Rhizophora trunks increased their nitrogen concentration to approximately 2.5 times the level in live trunks, and they maintained high nitrogen concentrations for more than 15 years (the length of the study).

Understanding of phosphorus cycling in mangroves is much less complete than knowledge of nitrogen dynamics (Alongi et al. 1992). Given that in heavily affected areas no plants are left alive, no plants take up nutrients released by decomposing mangrove tissues. Immediately after the storm, an algal mat developed in areas of major canopy loss. By December 1993, even this algal mat had died. Phytoplankton blooms were reported in the second half of 1993 along the southwest Florida coastline and have been attributed to nutrients being released from the affected mangrove forests.²