Vegetation dynamics, landscape change, and land use history in northern Florida

In the Southeastern Coastal Plain, land use practices since European settlement have triggered broad changes in many forested ecosystems. The invasion of longleaf pine (Pinus palustris Mill.) forests by sand pine (Pinus clausa (Chapm. ex Engelm.) Vasey ex Sarg. var. immuginata Ward.) in the Florida Panhandle is one such change in the landscape. This dissertation examined the interaction of natural and anthropogenic disturbances and population dynamics that fostered this invasion. Aerial photographs (1949, 1994) and geographic information systems (GIS) analyses were used to determine the historical and current extent of sand pine, as well as the nature of sand pine expansion. I collected forest structural and compositional data to examine the processes underlying sand pine expansion.; GIS analyses confirmed sand pine expansion and also indicated increased canopy cover of sand pine over time. Transition probabilities showed the high rate of conversion of longleaf pine to sand pine from 1949 to 1994 and conversion of less dense sand pine stands to dense sand pine stands. Correlations between sand pine distribution and physical site characteristics showed the pattern of invasion as sand pine expanded inland and upland into longleaf pine forests. In 1949, sand pine was preferentially located on sites below 30 m in elevation; by 1994, sand pine stands were found on all elevation classes.; The stand level analysis confirmed that the oldest sand pine populations were located near the coast and along the riparian forests. Population establishment and growth in invasive stands has been rapid, with the establishment of many pioneer individuals followed by infilling as individuals reached reproductive maturity. Sand pine will likely persist in these communities due to the abundance of sand pine regeneration. Hemispherical canopy photographs and regeneration patterns illustrated the ability of sand pine to establish under a variety of light conditions. Radial growth analysis of incremental tree cores highlighted the importance of episodic local disturbances in maintaining these sand pine populations. Historical information indicated that grazing pressure, fire regimes, turpentining and logging activities, and climate interacted to affect the regeneration capabilities of longleaf pine and favor sand pine, which reproduces rapidly.