Non-Forested Wetlands

In general, fire-adapted systems that have a more open structure and composition are less prone to high-severity wildfire. Frequent low-severity fire has also been shown to promote many species projected to do well under future climate projections, such as shortleaf pine and many oak species. Fire-suppressed systems, on the other hand, tend to have heavy encroachment of woody species in the understory that reduce regeneration potential for these fire-adapted trees. In addition, fire-suppressed systems can be more vulnerable to insect attack.

Habitat fragmentation can hinder the ability of species to migrate to more suitable habitat on the landscape, especially if the surrounding area is nonforested. Modeling results in this assessment and elsewhere indicate that trees would need to migrate at rates of hundreds of feet to several miles per year to keep pace with the changes in climate that are projected to occur over the next century. Species in community types that tend to be more rare and fragmented may be at a particular disadvantage.

Species-rich communities have exhibited greater resilience to extreme environmental conditions and greater potential to recover from disturbance. Conversely, ecosystems that have low species diversity or low functional diversity (where multiple species occupy the same niche) may be less resilient to climate change, its associated stressors, or both. Genetic diversity within species is also critical for the ability of populations to adapt to climate change, because species with high genetic variation tend to have more individuals that can withstand a wide range of environmental stressors

Increases in drought, invasive plants, insects, disease, and wildfire are expected to negatively affect forest productivity in some parts of the region. Lags in migration of species to newly suitable habitat may also result in reduced productivity, at least in the short term. However, some of these declines may be offset by the positive effects increased carbon dioxide (CO2) has on photosynthetic rates and water use efficiency, and by a longer growing season.

Model results suggest an increase in suitable habitat for many species at or near the northern extent of their current range, including shortleaf pine, post oak, and blackjack oak. In addition, habitat may become favorable to species not currently found in the assessment area, such as loblolly pine. However, habitat fragmentation and the limited dispersal ability of seeds are expected to hinder the northward movement of the more southerly species despite the increase in habitat suitability. Most species can be expected to migrate more slowly than their habitats will shift.

Results from climate impact models suggest a decline in suitable habitat for northern species such as sugar maple, white ash, and American beech when compared with habitat suitability under current climates. These northern species may be able to persist in some southern portions of their range if potential new competitors from farther south are unable to colonize these areas, although they are expected to have reduced vigor and be under greater stress.

A warming climate is allowing some invasive plant species, insect pests, and pathogens to survive farther north than they had previously. One particular emerging threat to the region is the southern pine beetle, which attacks shortleaf and other pines. Oak decline, a disease complex brought about by droughtand other stressors, is expected to become a larger problem in the red oak group as droughts become longer and more widespread. Some drought- and fire-tolerant invasive plants, such as sericea lespedeza, may also benefit from projected climate changes.

At a global scale, the scientific consensus is that fire risk will increase by 10 to 30 percent due to higher summer temperatures and occasional increased periods of droughts. Projections for the central United States show low agreement among climate models on changes in fire probability in the near term, but the majority of models project an increase in wildfire probability by the end of the century . Fire seasons in the southeastern United States could nearly double in length and increase in severity.

Due to projected decreases in precipitation during summer or fall and increases in temperature throughout the year, some evidence suggests a slight decrease in surface soil moisture in the Central Hardwoods Region over the next century . In addition, total soil moisture is projected to increase during winter and spring and decrease in the late summer and autumn. Even if there are increases in precipitation in the summer, as a few models suggest, increases in evapotranspiration are projected to lead to lowersoil water availability .

Heavy precipitation events have already been increasing in number and severity in the area, and some models suggest an increase over the next century .