Monitoring Recruitment of Native Species, Exotic Plant Occurence, and Erosion in the Big Lagoon Burn Area, Horn Island, Mississippi, Gulf Islands National Seashore

Brewer, J.

On April 22, 2001, an arson fire was ignited around the Big Lagoon area of Hom Island and burned 108 acres before it was contained three days later. The effects of the Big Lagoon Arson (BLA) fire on native and invasive plant species were monitored between June 1 and November 23 of 2002. The populations of three native plant species, Florida Rosemary, Ceratiola ericoides, Woody Goldenrod (Chrysoma pauciflosculosa), and Slash Pine (Pinus elliotti) were severely and adversely affected by the fire. All three were woody perennials with little or no capacity for resprouting following damage by fire. Within the area of containment, between 48 and 51% of all Rosemary shrubs and between 27 and 35% of goldenrod shrubs present (including seedlings, juveniles, and reproductively mature adults) were killed by the fire. Approximately 54% of all slash pines within the burned area were killed by the fire, including over 40% of the large reproductively mature trees. There was no evidence of recruitment of Florida Rosemary and very little recruitment of Woody Goldenrod or Slash Pine in the burned area in 2002. Age distributions of all three species in adjacent unburned areas, along with the lack of significant recruitment in burned areas since the fire, strongly suggest that recruitment of these species typically occurs more or less continuously on Hom Island and does not require frequent fires. Rather, the BLA fire most likely reduced recruitment of all three species by killing existing recruits and reproductive adults. Model projections suggestthat repeated fires with effects similar to those of the BLA fire will likely drive rosemarypopulations to extinction. More data on recruitment and mortality are needed, however,to evaluate these predictions with an acceptable degree of confidence. In contrast to the three native species mentioned above, most native perennial grasses, forbs, and shrubs resprouted and survived the fire (although none showed increased flowering), as did all three non-native invasive species, Torpedo Grass (Panicum repens), Chinese Tallow Tree or Popcorn Tree (Sapium sepiferum), and Cogongrass (Imperata cylindrica). Some native relic dune species (i.e., Balduina angustifolia, Cnidoscolus stimulosus) showed increased recruitment following the fire, apparently benefiting from the increased mortality of Florida Rosemary. Results of this study suggest that a change in fire management policy on Hom Island is warranted, whereby active suppression of all fires is abandoned in favor of suppressing only those fires that were most likely started by humans. In addition, a program of regular prescribed burning throughout the island is argued to be unnecessary and ill-advised, given the sensitivity of the dominant relic dune plant populations to fire and the absence of plant species that depend on frequent fires to persist. Horn Island remains a relatively pristine island preserve that lacks many of the pressures to implement programs of active fire suppression or regular prescribed burning on the mainland. Wildfire hazard reduction in the urban-wildland interface and protection of commercially valuable timber resources are not concerns on Horn Island. Furthermore, Hom Island lacks many of the unnatural "fire breaks" that characterize the mainland. Accordingly, Horn Island has unparalleled potential to serve as a valuable ecologicalreference point for monitoring natural fire regimes. A policy of permitting lightningstartedfires to burn naturally on Horn Island may come as close to mimicking a natural fire regime in a relatively pristine ecosystem as is possible in the southeastern United States.