The Ecological Classification of Coastal Wet Longleaf Pine (Pinus palustris) of Florida from Reference Conditions

Abstract

Tropical storms, fire, and urbanization have produced a heavily fragmented forested landscape along Florida’’s Gulf coast. The longleaf pine forest, one of the most threatened ecosystems in the US, makes up a major part of this frag- mented landscape. These three disturbance regimes have produced a mosaic of differently-aged pine patches of single or two cohort structures along this coastline. The major focus of our study was to determine reference ecosystem condi- tions by assessing the soil biochemical properties, overstory stand structure, and understory plant species richness along a patch-derived 110-year chronosequence in order to accurately evaluate on-going longleaf pine restoration projects. This ecological dataset was also used to classify each reference patch as mesic flatwoods, wet flatwoods, or wet sa- vanna. All of the reference locations were found to have similar soil types with no significant differences in their soil biogeochemistry. Mean diameter-at-breast height (DBH), tree height, and patch basal area increased as mean patch age increased. Stand growth reached a plateau around 80 - 90 years. Shrub cover was significantly higher in the mature- aged patches (86 - 110 years) than in the young (6 - 10 years) or mid-aged (17 - 52 years) patches, despite prescribed fire. Plant species diversity as indicated by the Shannon-Wiener index decreased with patch age. Soil biogeochemical properties, forest structure, and understory species composition were effective for ecologically classifying our pine patches as 55 % mesic flatwoods, 20% wet flatwoods, and 25% wet savanna. Florida’’s Gulf coastal wet longleaf pine flatwoods attain a structural and plant species equilibrium between 80 - 90 years.