Contrary to common perception, much of the southeastern United States was covered by grassland vegetation of various types prior to EuroAmerican settlement. This was particularly true for the southeastern Coastal Plain, where pine savanna/woodland covered roughly two-thirds of the landscape. However, grasslands were also prominent in inland subregions of the Southeast and included communities such as tallgrass prairies; shortleaf pine-post oak savannas; limestone, dolomite, sandstone, and igneous glades; shale and serpentine barrens and woodlands; river-scour prairies; high-elevation Southern Appalachian balds; coastal grasslands; and marl prairies of the Everglades. We conducted a wide-ranging literature review to determine the factors responsible for creating and maintaining grasslands across the unglaciated southeastern United States. This region receives far too much precipitation to meet the conventional explanation for a grassland biome as a region intermediate in rainfall between forest and desert. We were also interested in determining the factors responsible for the globally significant levels of species richness and endemism in these communities.
Results/Conclusions
Fires set by lightning and Native Americans were most important for maintaining grassland vegetation across the region, with frequent fire promoting high species richness by preventing competitive exclusion. Other factors, including geology, soils, wind disturbance, flood scour, hydroperiod, and large herbivores also helped maintain southeastern grasslands. Especially on a fine spatial scale, species richness in the Southeast peaks in pine savannas and related grasslands. More broadly, the primary centers of endemism in the Southeast are in the Coastal Plain, with approximately 85% of plants endemic to this subregion associated with pine savannas/woodlands or embedded communities. Besides site-level factors, the high species richness and endemism of southeastern grasslands can be explained by antiquity; historic biogeographic and evolutionary phenomena, including immigration of species from many different regions; allopatric speciation favored by sea-level fluctuations and isolation by rivers; and relative climatic stability over long periods. Grasslands in the Southeast have declined more than other vegetation types due to agriculture, fire exclusion and subsequent transition to forest, urban development, and other factors. We propose a comprehensive conservation strategy for southeastern grasslands focused on increased field and remote sensing inventories, ecosystem representation (through protection and restoration), and protection of endemism hotspots on multiple spatial scales.