Regeneration in fringe mangrove forests damaged by Hurricane Andrew
Mangrove forests along many tropical coastlines are frequently and severely damaged by hurricanes. The ability of mangrove forests to regenerate following hurricanes has been noted, but changes that occur in vegetation following disturbance by hurricane winds and storm tides have not been studied. We measured changes in plant community structure and environmental variables in two fringe mangrove forests in south Florida, USA that experienced high wind velocities and storm tides associated with Hurricane Andrew (August 1992). Loss of the forest canopy stimulated regeneration via seedling growth and recruitment, as well as resprouting of some trees that survived the hurricane. Initial regeneration differed among species in both forests: Rhizophora mangle L. regenerated primarily via growth of seedlings present at the time of the hurricane (i.e., release of advance recruits), but many trees of Avicennia germinans (L.) Stearn and Laguncularia racemosa Gaertn.f. resprouted profusely from dormant epicormic buds. In one forest, which was formerly dominated by Laguncularia, high densities of Rhizophora seedlings survived the hurricane and grew to form dense stands of saplings and small trees of Rhizophora. In the other forest, there were lower densities of surviving Rhizophora seedlings (possibly due to higher storm tide), and extensive bare areas that were colonized by Avicennia, Laguncularia, and herbaceous species. This forest, predominantly Rhizophora at the time of the hurricane, now contains stands of saplings and small trees of all three species, interspersed with patches dominated by herbaceous plants. These findings indicate that moderately damaged fringe forests may regenerate primarily via release of Rhizophora advance recruits, leading to single-species stands. In severely damaged forests, seedling recruitment may be more important and lead to mixed-species stands. Regeneration of mangrove forests following hurricanes can involve different pathways produced by complex interactions between resprouting capability, seedling survival, post-hurricane seedling recruitment, and colonization by herbaceous vegetation. These differences in relative importance of regeneration pathways, which may result in post-hurricane forests different from their pre-hurricane structure, suggest that models for regeneration of mangrove forests will be more complex than "direct regeneration" models proposed for other tropical forests where regeneration after hurricanes is dominated by resprouting.