An ecosystematic analysis of Carolina bays in the coastal plain of the Carolinas.

摘要

Carolina bays are elliptic, directionally aligned depressions occurring on the Atlantic Coastal Plain from New Jersey to northeast Florida. Eighty percent of those depressions are estimated to occur on the coastal plain of the Carolinas. Once only the subject of scientific study and debate in relation to their geologic origin, Carolina bays have increasingly drawn attention because of the exceptional biotic diversity of the lentic ecosystems they contain. This study sought to document the vegetational diversity that occurs within this seemingly uniform depressional environment, and to determine the environmental factors responsible for that variation.; Detailed examinations of community vegetational composition and environmental relationships in 482 intensively sampled, permanent plots located in 57 Carolina bay depressions are presented in this study. Cluster analysis of vegetation data grouped stands into 9 vegetation classes and 63 community types. Vegetation classes and subclasses represent a broad spectrum of southeastern coastal plain wetlands types, including, brackish marsh, freshwater pond, freshwater marsh, freshwater prairie, pocosin, bay forest, bog, swamp forest, depression meadow, cypress savanna, and longleaf pine savanna communities. Detailed, structured descriptions of the characteristics of each identified vegetation group type are presented and discussed in relation to the existing literature.; Nonmetric multidimensional scaling was used to examine community compositional gradients in relation to 69 environmental variables. Overall, vegetation was consistently correlated with "landscape hydrology", soil type and percent soil organic matter, and site disturbance regime. Specific vegetation groups exhibited distinctive, within group variation in response to soil nutrient and texture status, hydrologic regime, and site disturbance history.; Vegetation-environment relationships were also examined over five landscape surfaces representing different regimes of regional hydrology, geology, and soils. Environmental gradients within landscapes were generally consistent with overall study area gradients. Additionally, the distribution of major vegetation groups was examined in relation to site hydrologic regime, fire frequency, soil type, and characteristic plant life forms and growth forms.; Carolina bay depressions, once thought to number in the hundreds of thousands, are substantially rarer than previously believed. I estimate that fewer than 900 bay depressions with relatively unaltered site hydrologies remain within the study area. Those that do remain continue to disappear at an alarming rate. North and South Carolina bay depressions are important refugia for wildlife and for plant populations, including more than 65 "special status" plant species. Field observations and pertinent literature indicate that bay vegetation at relatively intact sites is highly dynamic, and that depression vegetation responds dramatically to differences in site disturbance regimes. Development of surrounding upland areas has resulted in increased isolation of Carolina bay depressions from the once pervasive role of fire as a landscape disturbance factor, and in the lowering of regional water tables. Consequently, bay vegetation has undergone an apparent "homogenization", with concomitant decreases in species richness and community diversity. If Carolina bay biodiversity is to be conserved and protected, increased and immediate attention must be given to prioritization, acquisition, and restoration of bay systems.