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Forest Ecology and Services

The diversity of forest settings in the South supports a diverse biota and contains 1,027 native terrestrial vertebrates (fig. 14): 178 amphibians, 504 birds, 158 mammals, and 187 reptiles. Species richness is highest in the Mid-South (815) and Coastal Plain (691), reflecting both the large area of these subregions and the diversity of habitats within them (chapter 14). The geography of this diversity varies by taxa. Amphibians flourish in portions of the Piedmont and Appalachian-Cumberland highlands and across the Coastal Plain. Bird diversity is highest in the coastal and wetlands forests along the Atlantic Ocean and Gulf of Mexico, mammal diversity is highest in the Mid- South and Appalachian-Cumberland highlands, and reptile diversity is highest in forests farthest south.

Figure 14—County-level counts of native terrestrial vertebrate species in the Southern United States. Source: NatureServe 2011.

The long history of intensive land use has changed the habitat structure of many southern forests. The near elimination of once-dominant longleaf pine ecosystems was perhaps the greatest ecosystem alteration resulting from intensive forest management and land use conversion in the South. Because of losses in this and several other upland and wetland forest ecosystems, southern species considered to be of conservation concern now include 152 terrestrial vertebrates, 81 of which are federally listed; and more than 900 plants, 141 of which are federally listed (figs. 15 and 16). Species of conservation concern include those that have a Global Conservation Status Rank of “vulnerable (G3),” “imperiled (G2),” or “critically imperiled (G1)” as described in chapter 14. The proportion of these species at risk varies among taxonomic groups (fig. 16): 45 percent of imperiled vertebrate species are amphibians, followed by reptiles (24 percent), mammals (16 percent), and birds (15 percent). The Coastal Plain (64) and Mid-South (55) lead in the numbers of imperiled vertebrate species (fig. 15), followed by the Appalachian-Cumberland highlands (31), Piedmont (29), and Mississippi Alluvial Valley (9).

Figure 15—County-level counts for terrestrial vertebrate species of conservation concern in the Southern United States. Source: NatureServe 2011.

The recent influx of nonnative invasive plants, insects, and diseases has been an unwelcome addition to southern forests. Of the most important invasive insects and diseases affecting southern forests, several have been established in the last 10 years (chapter 16), e.g., emerald ash borer and laurel wilt have been introduced only recently and are spreading rapidly throughout the range of their host species.

Of the 380-plus recognized nonnative plants in southern forests and grasslands, 53 are rated high-to-medium risk for natural communities (chapter 15). These plants often out-compete native species and alter species composition of forests, resulting in impacts to forest productivity, diversity, and wildlife habitat that can be exceedingly difficult to manage, especially when multiple species are involved. As a group, their distribution is southwide, though occurrence and concentration of individual species within subregions is variable (fig. 17).

Strong population growth and associated urbanization has increased demand for water and challenged water availability in several areas, especially in the Piedmont, throughout Florida, and in much of Texas (fig. 18). Conversion of forests to urban and other land uses has resulted in a loss of natural buffering, increasing water pollution loads, elevating peak flows, and reducing base flows in affected watersheds. The consequences are more frequent and more severe flooding, lower stream flows during drought conditions, and water quality that is degraded— sometimes to the point of threatening public health. Although the degree of adverse hydrologic responses to urbanization differs across subregions, the link between conversion of forest land to urban uses and degraded water quality in affected watersheds is well documented (chapter 13).

Figure 16 – Number of species of conservation concern (the sum of vulnerable, imperiled, and critically imperiled species) in the Southern United States for (A) terrestrial vertebrates and (B) vascular plants. Source: NatureServe 2011.

Figure 17—Percentage of forested survey plots in which one to four nonnative invasive plant species were reported in the Mid-South, Mississippi Alluvial Valley, Coastal Plain, Appalachian-Cumberland highlands, and Piedmont. Source: USDA Forest Service, Forest Inventory and Analysis databases.

Figure 18—Water supply stress index (defined by the Water Supply Stress Index or WaSSI and calculated by dividing water supply into water demand) under baseline (1995–2005) conditions. Darker colors indicate higher levels of stress (see chapter 13 of the technical report of the Southern Forest Futures Project).

To recap, forests dominate much of the South’s landscape and play a critical role in the lives and livelihoods of the region’s populace. Forest types and the species they support are highly diverse, reflecting a range of biophysical conditions. The South leads the United States in timber production, and intensive management has expanded the productivity of its pine forests. Southern forests also provide a variety of ecosystem services including clean water, biodiversity, and carbon storage. Although timber inventory has increased over the past 2 decades as a result of management, there are indications that increases may have come at a cost to some ecosystem services. Diverse values and dynamic forest conditions combined with high uncertainty about the future give rise to the questions that have been the focus of the Southern Forest Futures Project.

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Key Findings

Forestry Sciences Laboratory

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