Effects of chronic human activities on invasion of longleaf pine forests by sand pine

Chronic human activities may result in new and permanent successional traje ctories in certain ecosystems. Tho invasion of longleaf pine ecosystems by sand pine in the Florida Panhandle is one such change in the landscape. Thi s study examined the spatial pattern of sand pine expansion and explored th e natural and anthropogenic disturbances that fostered this invasion. Aeria l photographs (1949, 1994) and Geographic Information Systems analyses conf irmed sand pine expansion at Eglin Air Force Base. In 1949, there were 8,98 2 ha of sand pine in the southern portion of the study area near riparian a nd coastal lowland forests. By 1994, sand pine had expanded further upland and inland, for a total of 17,147 ha in the study area. Sand pine age data showed that this expansion had started by 1920 but increased rapidly in the 1940s. Historical accounts and structural data from stands suggest that la nd-use activities associated with the extraction of turpentine promoted the invasion by sand pine. Fires were suppressed in longleaf pine forests to p rotect turpentine trees, resulting in increased vegetation cover and decrea sed regeneration of longleaf pine. In addition, stands were typically harve sted after turpentining, and there was little or no advanced regeneration o f longleaf pine. Sand pine age histograms showed that the onset of high est ablishment rates (1940s) coincided with changes in land ownership and wides pread fire suppression. Sand pine is likely to persist in these ecosystems due to its abundant regeneration.