Volume of woody debris in forests provides an often overlooked, yet important, ecosystem service. The slow recovery, or decomposition, of woody debris following a major disturbance, such as a hurricane, has led to speculation that coarse woody debris serves to influence positively the long-term persistence and supply of nutrients in a forest ecosystem. Hence, immediately after a disturbance an acute flux of nutrients via litter and small woody debris fall occurs. This initial flux is followed by a gradual decrease in the supply of nutrients to some steady state whereby larger woody debris provides a source of nutrients during the ensuing forest recovery period when nutrients are most needed.

Woody debris is abundant in hurricane-prone forests. With a major hurricane impacting south Florida mangroves approximately every 20 years, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential.

Here, we report on line-intercept woody debris surveys conducted in mangrove wetlands of south Florida 9-10 years after the passage of Hurricane Andrew (1992). The volume of woody debris for all sites combined was estimated at 67 m3ha^-1, and varied from 13 - 181 m3ha^-1 depending upon differences in forest height, storm circulation quadrant, and maximum model-generated wind velocities. The greatest amount of woody debris was found in the eyewall region of the hurricane, with a projected necromass of about 36 t ha^-1. Approximately half of the woody debris biomass was associated as small twigs and branches (fine woody debris) since much of the coarse woody debris > 7.5 cm was fairly well decomposed. Regressions of woody debris relative to forest height and maximum Hurricane Andrew windspeeds were developed so that woody debris can be added to existing ecological simulation models for the region. Including woody debris in model simulations may be important in accounting for a substantial amount of additional carbon within the system.

Cases of Caribbean mangrove tree mortality have been reported but have not included estimates of downed wood. Downed woody debris as a component of mangrove forest structure has been explored in two investigations from the old world tropics but have less relevance to neotropical mangrove swamps. This research provides those data for hurricane-prone regions of south Florida and provides the associated link to ecological simulation models.

Contact: Ken W. Krauss, U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, LA, 70506, Phone: 337-266-8882, Fax: 337-266-8592, Email: kkrauss@usgs.gov, Poster, Ecology and Ecological Modeling

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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