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- Info
Southeast
| Author: |
White, Peter S.; Wilds, Stephanie P. |
| Date: |
1998 |
| Periodical: |
In: Mac, M.J.; Olper, P.A.; Haecker, C.E.P. [and others],eds. Status and trends of the Nation\\\'s biological resources. Washington, DC: U.S. Department of the Interior, Geological Survey |
| Abstract: |
The ecosystems of the Southeast range from the spruce-fir forests of the highest mountains east of the Mississippi River to the tropical hardwood hammocks of southernmost Florida. A tremendous diversity of ecosystems lies between these extremes: the sawgrass marshes, mangrove forests, and pine rockland of south Florida; the carnivorous plant wetlands, baldcypress swamps, live oak maritime forests, longleaf pine savannas, and duties of the Coastal Plain: the oak-hickory forests, bottomland forests, prairies, glades, and barrens of the Piedmont and continental interior: the springs and extensive cave systems of limestone areas; and the old-growth deciduous and hemlock forests, cliffs, rocky streams gorges, and grassy and heath balds of the southern Appalachian Mountains.
Althouah broad-scale climatic patterns explain much of this diversity, the Southeast\'s most distinctive characteristic is diversity at small scales. Variation in topography determines soil moisture and temperature regime, influences soil fertility, and produces change in ecosystem composition and structure over relatively short distances. The Southeast is also underlain by a wide variety of geological substrates and soils; thus, where ecosystem boundaries are abrupt, a mosaic of community types results. Usually, however, changes in community types are gradual, and classification of community types itself becomes arbitrary. Many animal species move among and depend on the diverse aquatic and terrestrial habitats of southeastern landscapes.
In addition to environmental variation, there are other explanations for the Southeast\'s biological diversity. Historically, the Southeast was not covered by continental glaciers, nor was much of the present land surface submerged by past rises in sea level. As a result, plants and animals have
evolved in the Southeast over long periods. This long evolution, combined with the isolation that characterizes some habitats has produced striking levels of endemism (species restricted to certain habitats) in many groups of plants and animals. Narrowly restricted endemism is most prominent in groups with limited dispersal ability and those found in isolated habitats. For example, narrow endemism is frequent in plants, amphibians, fishes, mollusks, and aquatic insects in the Southeast but is weak in birds and mammals.
Because of diverse environments and long evolutionary isolation, a number of groups reach continental high points of species richness in the Southeast, making the region one of the richest areas in the temperate zone, surpassed only by eastern Asia (Hackney et al. 1992; Martin et al. 1993a,b). Groups that have their highest North American diversities in the Southeast include amphibians, fishes, Mollusks, aquatic insects, and crayfishes throughout the region; salamanders, land snails, fungi, and plants in the Southern Appalachians; and carnivorous plants on the Coastal Plain.
This chapter describes the status and trends of the rich biological diversity of the Southeast. The very diversitv and local complexity of the region\'s ecosystems complicate our task. Long-term data are scarce and often are available for only a few study areas\'or taxonomic groups. The trends that are available are usually derived from expert opinion rather than extensive data sets and often concern loss of habitat area rather than change in populations or ecological processes (Noss et al. 1995). Our emphasis is on ecosystems because they are the best context for the consideration of biological diversity, but we also summarize status and trends for vertebrates and several other well- studied groups. |
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