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Forests of the Southeast are diverse and among the most productive in North America. They form the basis for a large timber and wood-products industry. However, minor to profound impacts could be in store for this region's forests if climate change results in: shorter winters; longer, drier summers; increased frequency of flooding; and summer droughts.
This region's forests are important resources for residents of the Southeast and for the global community. In addition to the inherent value of the forests and the ecosystem services such as flood control that they provide, forests in the region provide habitats for wildlife, recreation and hunting venues for humans, and wood and fiber for a variety of uses. Loblolly-shortleaf pine forests of this region's south-central states are the most prevalent eastern pine ecosystem and one of the most productive. The shortleaf pine is found outside the range of the loblolly and mostly in Arkansas, Texas, Mississippi, and Alabama. The longleaf-slash pine forests are found mostly in Florida and southeastern Georgia. The southern bottomland hardwood forests of Louisiana, Mississippi, and Alabama cover 5.2-million acres along waterways and wetland areas.
The ability of trees to store carbon is essential to the productivity of forests. To the extent that forests store carbon for the long-term, by withdrawing carbon from the atmosphere, forests help to offset carbon dioxide emissions. The Southeast region's loblolly pine forests sequester about 75 tons of carbon per acre per year, while forests in the south-central states store approximately 60 tons of carbon per acre per year. Plantations that harvest their forests every 50, 75, and 100 years tie-up 38, 44, and 51%, respectively, of the carbon that an old growth forest stores, which is over 240 tons per acre. Forest soils store the largest portion of carbon in forest ecosystems -- totaling 29 billion tons of carbon in the US.
The productivity of southeastern forests will depend on the changes in temperature and precipitation. If the warm, moist conditions projected by one of the models prevail, there will be virtually no water stress through the 21st century, and the productivity of this region's forests will increase. Forest models project that the productivity of the southern loblolly pine plantations would increase approximately 11% by 2040 and 8% by 2100 under such conditions, and the productivity of hardwood and mixed pine hardwood forests is projected to increase 22% by 2040 and 25% by 2100 compared to 1990 levels.
The model studies indicate that the greatest increases in productivity of both pines and hardwoods would occur in the northern half of the region. However, if the hot, dry conditions projected by the other model prevail, decreases in productivity are projected in parts of the Southeast. These results also suggest the possibility of a breakup of the pine-dominated forests in parts of the Southeast by the end of the 21st century. The breakup of the forest would lead to some forested areas being replaced by savannas and grasslands as a result of decreased soil moisture and fire.
Whether the warm, moist or the hot, dry conditions occur, additional factors are likely to contribute to disruptive influences on the forests. For example, the southern pine beetle reproduces more rapidly in prolonged hot and dry weather, a time that is also well-suited for forest fires. Other potential disturbances to forests include damaging fungus thriving in warm, moist weather, and storm damage to coastal forests that could increase in the event of higher incidences or more severe coastal storms. In addition, fluctuations in fresh water level could hinder the ability of southern bottomland hardwoods, which play a vital role in erosion control, to handle high peak flood and large storm events.
Climate change in the Southeast could also affect growth rates of individual trees as a result of warming, changes in regional moisture balance, or extreme events. Altered river flows, flooding, and hurricanes, can also result in increases in tree mortality and invasion of exotic (non-native) species. For example, a 1986 hurricane resulted in a small rise in the mortality of forest canopy trees, which then promoted the growth of native and non-native woody species, typified by small trees and shrubs. As canopy trees perish, the long-term result is often a decline of the carbon-storage capacity of southern upland forests due to their replacement by small trees and shrubs.
Rising sea levels are already causing loss of coastal forests. Throughout coastal areas in Louisiana and South Carolina, bald cypress forests are being lost to increased flooding and saltwater intrusion. Moreover, non-native species, such as the Chinese tallowtree, are taking over available habitat in these seasonally flooded coastal areas. Although these species are more salt-tolerant, they are less able to survive hurricane-force winds, possibly increasing the vulnerability to potential flooding and erosion. Like the bald cypress forests, hundreds of thousands of sabal palms are also dying along the low-lying coastal areas of Florida, a loss scientists' attribute to saltwater intrusion.
The eastern softwood forests are important for commercial purposes, recreation, wildlife, and hunting. The southern bottomland hardwood forests of the Mississippi Delta serve a critical role in erosion control, flood prevention, and as flyways and habitats for millions of migratory birds. The underbrush of the southern bottomland hardwood forests provides habitat for waterfowl, migratory songbirds, squirrels, white-tailed deer, and wild turkey, which all support an active hunting community and economy.
Eighty percent of this once vast system of hardwood forests has already been lost to clearing, draining, leveling, and agriculture projects that began in the mid-1930s. Further changes to these forests could have significant effects on species, hydrologic regimes, soil erosion, and water quality. Agricultural conversion of this critical forested region has been stopped in an effort to re-establish the southern bottomland forests.
Just as these forests are important in flood control, the bald cypress forests serve as a vital buffer from hurricane winds. Researchers are working to find more salt-tolerant strains of bald cypress to restore the aesthetic beauty of these forests and to provide a natural buffer to protect life in coastal areas.
Softwoods are the East Coast's most important commercial timber forests, and the loblolly pine is the basis for a large and expanding lumber and wood-fiber industry. Should the future losses in pine productivity across the region occur, this could be economically significant because they presently cover nearly two-thirds of the region's forest industry land and account for about one-half of the Nation's softwood inventory. Because of this they are more commercially valuable (pulp and paper) than the region's hardwoods. The slash pine is a commercially valuable species that is found on wetter sites that are protected from fires. Southern bottomland hardwood forests support a variety of tree species of high-quality wood and economic value, including cottonwood, cypress, tupelo, sycamore, red oak, green ash, sugarberry, and sweetgum. Coastal forests, such as bald cypress, produce valuable timber that is important because of its rot resistance. In Louisiana in 1948, bald cypress provided 49 million board feet but only four million board feet in 1977. Most of this reduction was the result of logging, but of greater concern today is that many cypress swamps logged 30 to 100 years ago have not regenerated.
Increases in temperature, changes in precipitation, and altered hydrology (water cycle) could change the economics of production and lead to disturbances and changes in forest composition. These effects are likely to result from salinity, submergence, pests, droughts, and fires. In commercially managed forests, if disturbance rates are increased, this could result in even higher timber losses. However, managed ecosystems, such as pine plantations have the potential to be more resilient to climate changes; if they flourish, this could ensure economic success for the region.
Strategies to cope with potential climate-change effects on forests of the Southeast could include any of the following options:
Other strategies could create incentives to maintain and protect private forestland. This could include efforts to:
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