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Abundant Forest Communities

Primary Question (chapter 17): How have biological agents, including insects and disease, influenced the overall health of the South’s forests, and how will they likely affect it in the future?

Related Questions (chapter 1): What are the history, status, and projected future of terrestrial wildlife habitat types and species in the South? (chapter 2): What are the history, status, and projected future of native plant communities in the South? (chapter 4): What are the historical and projected future impacts of forest management and access on terrestrial ecosystems in the South?

Analysis of changes in forest types indicates ongoing transformation of forest conditions. The area of upland hardwoods is forecast to decline somewhat between 1995 and 2040, but will remain the forest type with the greatest area. Pine plantation acreage is forecast to increase through planting of agricultural land and harvested natural pine and hardwood forests. Though these communities are considered abundant, they face continuing health challenges. Also, because of their extent, their structure and condition are especially important to the region’s wildlife. The value of these forest types as habitat for wildlife depends largely on how they are managed.

Pine types—Pine planting will continue to be focused in the Coastal Plain and parts of the Piedmont, but we expect planting rates to increase the most in the western half of the region. Forest structure in plantations differs from that found in naturally regenerated stands. Their management is designed to focus site potential to maximize the growth of trees of a single species, and trees are spaced to maximize fiber production over a 20- to 30-year period. Retaining a narrowly focused stand structure requires considerable management effort. This is evidenced by about 2.5 million acres of plantations transitioned to other forest types since the 1980s. Thus, over time and without intervention, plantations often become more diverse in terms of tree species composition. Their value as wildlife habitat will vary depending on the type and variety of vegetative species that diversify the stand. This increased diversity is greater in plantations established following harvest of natural pine or oak-pine forests, because they retain biological legacies from the preceding forest type, especially when plantations are mixed in with naturally regenerated forests and wetlands as in the Carolina Coastal Plain. Plantations established on converted agricultural sites can develop considerable grass and forb diversity in early stages, but because they lack the biological legacies of earlier forests, their vegetative diversity is limited for a longer period of time (chapter 4). Very dense stocking and use of herbicides can limit vegetative diversity throughout the entire rotation. The intensity of forest management has various effects on wildlife suitability. In addition to differences in forest structure, intensive pine management generally involves more frequent management activities. Depending on the circumstances (such as type of legacy, management strategy, density of stocking, use of herbicides, prescribed burning), these actions can disrupt, benefit, or have little effect on wildlife. Effects of management activities on wildlife are discussed in “Recreation.”

Another less commonly recognized phenomenon associated with intensively managed forests is their invasion by exotic plants; additionally, other land uses have contributed to the spread of exotics in the South. Privet, kudzu, and other exotic shrubs and vines displace native plant species and vary in their benefit to wildlife. Kudzu and Japanese honeysuckle alone now occupy more than 7 million acres of land each (chapter 3). In some areas, exotic vines can completely dominate the shrub and herb layer.

Expanded areas of pine forests in parts of the South have increased the availability and contiguity of host material for certain native pest insects and pathogens, especially southern pine beetle. However, short-rotation lengths and active management minimize what would otherwise be increased infestation risk. Damage from these pests is likely to be greatest in plantations that are not actively managed following establishment. These most commonly occur on nonindustrial private ownerships. Pest-appropriate management activities—which may include lower stocking rates, use of prescribed burning, active pest suppression, and sometimes reducing the frequency of stand-disturbing activities—may lower the risk of spreading infestations in these types of forests.

Overall mortality rates for softwoods have increased from about 0.6 percent of inventory per year in the 1960s to 1.0 percent per year in the 1990s. We expect pine mortality to remain high, especially at the periphery of the natural range of many pine species—for example, in Tennessee, Kentucky, and Virginia. In these areas especially, southern pine beetle will remain problematic for forest managers.

With respect to forest pests associated with pine types, we found that (chapter 17):

• Five native diseases in the South have substantial impact on forests and two—annosus root disease and fusiform rust—have substantial commercial impacts on pine species. Fusiform rust is in epidemic status along the Coastal Plain from Louisiana to South Carolina (fig. 41). It causes heavy mortality of slash and loblolly pines. Annosus is more localized and limited by site factors, but it can cause severe root disease in thinned stands if not treated. Littleleaf disease targets shortleaf pine and has encouraged the conversion of shortleaf sites to loblolly pine.

• Several native insects have substantial influence on forests. The insect with the most substantial economic impact and habitat impacts for the endangered red-cockaded woodpecker is the southern pine beetle, which reaches epidemic levels at irregular intervals and causes high rates of mortality over broad areas (fig. 11). It prefers shortleaf and loblolly pine forests, but also attacks other pine species. Longleaf pine, while susceptible, does not appear to be a preferred host species.

• Mature pine trees are more susceptible to damage from southern pine beetle than younger trees, so that public forests, with higher concentrations of older, more mature pine forests, are most likely to be attacked. Spillover of epidemics onto adjacent private land will continue to be a significant resource management issue for public forests in the South. Likewise, planted pine on nonindustrial private forest land with little management experiences higher mortality from southern pine beetle. The risk of damage can be reduced by utilizing management practices that reduce stocking.

Upland hardwoods—The upland hardwood type gradually expanded in the South between the 1950s and the 1990s but has been in a state of flux for more than a century. Many areas were permanently transformed by chestnut blight, which eliminated American chestnut from its dominant role in mountain forests in the eastern portion of the South beginning in the 1930s. Recent expansion of upland hardwood acreage has resulted from a combination of natural succession of pine forests and removal of the pine component from mixed pine-hardwood forests. Currently, the greatest expanses of the upland hardwood types (generally oak-hickory) are concentrated in the Piedmont, the Appalachian Mountains, the Ozarks, and the Cumberland Plateau. Urbanization, along with increased harvesting of hardwood timber, will continue to modify these forests in important ways, especially in the Piedmont. While the area of upland hardwoods is forecast to decline only slightly over the next few decades, it is likely that these forests will become more fragmented in some areas, and in these places, will provide less interior forest habitat. In addition, indirect human influences related to increased population density will also be felt in these areas.

As with softwood forests, pathogens and insects have had important effects in hardwood forests, and they continue to spread within the South. As was the case with chestnut blight, most of these organisms are nonnative, or exotic, and control options are either ineffective or limited in their potential application.

• Oak decline, a disease complex affecting oak species, could have long-term consequences for the species composition of hardwood forests in the South. It is prevalent in areas where oak species occupied the niche of American chestnut eliminated by the chestnut blight beginning in the 1930s. It is becoming especially widespread in the mountainous areas of the Southern Appalachians and the Ozark and Ouachita Highlands, on dry and infertile sites. Drought appears to worsen its effects.

• Four exotic diseases have had or will have substantial impact on southern forests (chapter 17). Each targets a single genus or species. Chestnut blight restructured Southern Appalachian forests, and the resulting trajectory of change has not completely played out. Based on current spread rates, beech bark disease is expected to cause substantial mortality to American beech and change its location in southern forests over the next 20 to 30 years. Butternut canker may completely eliminate butternut from southern forests. Dogwood anthracnose has already led to widespread decline of dogwoods with resulting aesthetic, economic, and wildlife implications (see fig. 42A, fig. 42B, fig. 42C and fig. 42D).

• The hemlock woolly adelgid kills both the eastern and the Carolina hemlock and is currently moving down the Blue Ridge from the Shenandoah Valley. It threatens both species’ occurrence in the wild. (chapter 3, chapter 17).

• The gypsy moth continues its steady march from the North and is currently moving from Virginia into North Carolina. Based on current spread rates, this insect is expected to progress across the South over the next 20 to 30 years. Epidemics can last several years in a particular location and lead to the defoliation of most species, but oaks are most susceptible. Considerable alteration to forested ecosystems, including loss of hard mast, is expected where gypsy moth damage coincides with oak decline (chapter 17).

Many of these forest health concerns can be complicated by the exclusion of fire. Absence of fire can alter species composition, but its reintroduction is difficult because much of the upland hardwood forest type occurs in or near heavily populated areas. Compounding the challenges of maintaining healthy hardwood forests is expected increased tree mortality that would increase fuel loadings and the risk of severe fires.