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The Current Condition of Native Plant Communities in the South

Ecosystems—In the Southeastern United States, interacting aggregations of plant and animal communities and the abiotic factors affecting them are as diverse as any in the World. No place in North America has more diverse forests in terms of plants or animals, or more different types of forests. One very important source of this diversity in plant communities in the Southeast is the exceptionally high degree of endemism (occurrence restricted to a particular region or area) in the regional flora, especially in Coastal Plain conifer forests and in Appalachian forests.

In contrast, the South has the greatest absolute number of introduced plant species in North America. Florida alone reports 800 introduced species existing outside of cultivation (FLEPPC 2001).

One of the most important tools in the study of any system, including plant communities, is a comprehensive means of classifying the observed diversity. Several large-scale vegetation classification methods are in current use; the most important are those described by Kuchler (1985), Bailey (1994, 1998), and The Nature Conservancy (TNC) (1999). Each of these systems divides the region on the basis of either general physiography or potential natural vegetation. Although many other methods exist, these methods illustrate the basic philosophies of large-scale vegetation classification. Although most vegetation classification systems are in agreement on the general distribution of regional plant communities, there is still much discussion and continuing research concerning how to define the transitions between vegetative communities.

Small-scale community classification can be generally useful in understanding the dynamics of local vegetation. Hierarchical and geographically comprehensive systems such as TNC’s National Vegetation Classification System (Anderson and others 1998, Grossman and others 1998) define literally thousands of plant associations based on the presence of dominant and associated species. The utility of this system (and similar systems) is its inherent flexibility.

One of the most useful qualities of TNC’s National Vegetation Classification System is the assignment of rarity ranks to plant communities (Association for Biodiversity Information 2001). A comprehensive system of rarity ranks across the Nation allows for an assessment of the geography of community diversity.

According to TNC figures, the Southeastern United States has the highest number of endangered ecosystems of any region of the country. More than 30 percent of all natural plant communities throughout the Southeast are critically endangered, and the Southeast has the highest proportion of imperiled plant communities in the United States, exclusive of Hawaii (Stein and others 2000). A great number of the rare plant communities in the Southeast are inherently rare, and their rarity is a function of the great plant diversity in the region. However, the majority of rare communities in the Southeast are rare because of habitat alteration or degradation.

The majority of inherently rare plant communities are relatively small patches of plants in unique combinations, often due to the presence of equally rare edaphic conditions. These patch communities can be seen as occurring within a matrix of more common, widespread community types. Most habitat conservation activities tend to focus on the patch habitats.

Because there has not been a single consistent convention for the identification of plant communities during the majority of the history of the Southeast, it is essentially impossible to discuss the specific changes to those plant communities over time. However, this is not to say that we cannot assess the overall trends in conditions of plant communities. On the basis of conversion, alteration, and impedance of function, more than 99 percent of all plant communities in the South are not in the condition they were in prior to European settlement. Some of these changes have been subtle, but most are readily distinguishable. It is impossible from the perspective of current times to know precisely what has been lost, but we can estimate the general loss sustained by southern native plant communities.

Among the communities to have seen the greatest change in historical times are the region’s forests. All of the forests of the South have been touched, directly or indirectly, at one time or another, by the hand of humanity. Sometimes that hand has been gentle, but in most cases it has not.

By some estimates, all of the upland hardwood forests of the Appalachians have been altered. The hardwood forests have suffered from chestnut blight, Dutch elm disease, and butternut canker. Even if the impact of disease is discounted, less than 10 percent of the original native forest area of the region has not been eliminated or altered. Most was cleared prior to the 1930s. Estimates vary from State to State, but, on average, approximately half of all presettlement hardwood forest has been eliminated (Walker and Oswald 1999), and the majority (essentially all) of what remains is compromised by fragmentation, exotic pest and disease organisms, and altered natural processes such as fire and livestock grazing (Mac and others 1998, Noss and others 1995).

Coastal Plains longleaf pine forests, renowned for their high levels of diversity, endemism, and species rarity, have been reduced by more than 98 percent, compared to presettlement conditions. Most have been converted to agriculture or pine plantations, two plant communities notable for their lack of diversity, endemism, and species rarity. Most of the longleaf pine forests were cut by the 1920s, but longleaf pine habitat was still being clearcut and converted into plantations in the 1980s (Noss and others 1995, Stein and others 2000). They were used as a source of timber since aboriginal times, but European settlers were clearcutting vast areas of longleaf pine by mid-18^th century. Longleaf that was not cut for lumber was commonly used as a source of naval stores beginning in the 17^th century, a practice that continued into the early 20^th century (Croker 1987). The remaining large blocks of longleaf exist almost exclusively in public forests (notable privately owned large tracts of longleaf include the Moody tract in southern Georgia and Green Swamp in North Carolina). Many areas of longleaf forests are being managed for the endangered red-cockaded woodpecker. Remaining blocks are, in some places, threatened by exotic plant species, such as Cogon grass (Imperata cylindrical), fire suppression, and some forestry (site preparation) practices that disturb the forest understory plants, in lieu of burning, to facilitate the growth of the trees. There is also much concern, but little that can actually be done, about the fragmentation of the original longleaf community (Croker 1987). Only minor fragmentation agents, such as roads, can be managed to increase longleaf habitat continuity, whereas the major fragmentation factors—conversion to agricultural and urban land uses—are essentially intractable. Many public land management agencies are currently practicing longleaf forest restoration activities, and others are encouraging restoration on private land. These efforts, while very important, vary greatly in their success. While it is relatively simple to successfully grow longleaf pine, the reconstitution of the original plant community is very difficult.

Fewer than 50 percent of the presettlement spruce-fir forests still exist in the Appalachians (Noss and others 1995). Of that quantity, more than 98 percent either have been altered or are under attack by introduced pests. Over 90 percent of the red spruce forests in central Appalachian forests have been lost (Noss and others 1995).

Approximately 90 percent of the forested habitats in Florida have been altered or eliminated, including 60 to 75 percent of the forested uplands of Lake Wales Ridge, an area of exceptionally high species rarity and endemism. Only on the Atlantic and Gulf coastal barrier islands does a majority of the natural forest cover remain. It has survived due to its isolation and unsuitability for agriculture or development (Noss and others 1995, Stein and others 2000).

More than 98 percent of the presettlement old-growth forests in the South have been altered or lost (Stein and others 2000). The vast majority of the remaining old-growth forests in the South are on Federal land in national forests and national parks. Of the original 60 to 90 million acres of Coastal Plain pinelands, only 3 percent survive today as old growth (Croker 1987, Noss and others 1995, Walker and Oswald 1999). Less than 2 percent of the forests in Kentucky have old-growth characteristics (Noss and others 1995). In Tennessee, only about 5 percent of the presettlement old-growth forest on the Cumberland Plateau remains, and no more than 20 percent of the forest of Tennessee’s Blue Ridge Province can be classified as old growth (Noss and others 1995). Those few tracts of old growth not on public land are mostly in fragments of 100 acres or less, which reduces their value (Stein and others 2000). Most of the forest types classified as old growth today are actually second- or third-growth forests that have or are developing the structural characteristics of old growth.

Open habitats in the South such as glades, barrens, and prairies were common at the time of European settlement, as noted by the earliest travelers to the region. There are, however, no good estimates of how much of the landscape was occupied by these open areas. The current best approximation suggests that as much as 10 percent of the plant communities of the South were historically open habitats (Mac and others 1998). Today, approximately 1 percent of the forested landscape of the South is occupied by openings such as barrens, prairies, and glades. In most cases these areas are very small, and they are not integrated across the landscape (Mac and others 1998, Stein and others 2000) as they once were.

Among open habitat types, prairies seem to have suffered the greatest losses. Settlers saw these relatively flat, treeless, and fertile areas as productive and easy to clear. In Kentucky, less than 200 acres of an original 3 million acres of native prairie remain (Noss and others 1995). In Texas, Louisiana, Florida, Mississippi, and Arkansas, nearly 99 percent of acres originally in prairie types have been lost (Noss and others 1995).

The majority of glades that survive today tend to occur in mountainous regions that were never converted to agriculture, and they typically have very stony soil. There is no information on the total area in glades throughout the region, but estimates are that less than half of the original glade habitat in the region survives intact, and the majority of that which remains is ecologically compromised due to either the presence of exotic species or the lack of fire. In Tennessee, approximately one-half of all the area in cedar glades has been converted (Noss and others 1995). Limestone glades throughout the region have been disturbed at higher rates (Noss and others 1995), probably because they are more commonly located at lower elevations and in areas of gentler topography.

High-elevation grassy balds are mountaintop treeless areas. Although the mountains on which these open areas occur are not high enough to have alpine plant communities, various edaphic and historical circumstances have conspired to keep these areas treeless. Grassy balds tend to support herb-rich communities that require frequent disturbance (Greller 1988). Their ecological origin is still a matter of debate. About 50 percent of the area that was occupied by grassy balds in 1900 remains today (Mac and others 1998).

Almost all of the wet hardwood forests, such as those that occur in bottomlands and hammocks on the tropical Coastal Plain, have declined to approximately 20 percent of their presettlement cover (Mac and others 1998, Noss and others 1995). A slightly larger percentage of the original floodplain forests has survived (Noss and others 1995), but most of it was cleared at some time in the past and has returned to forested cover in the last century. In the last 25 years, accelerated efforts have been made to restore floodplain forest, especially in the Mississippi Valley.

The Southeast comprises only 16 percent of the land area of the lower 48 United States, but it contains 36 percent of all wetlands and 65 percent of forested wetlands. About 78 percent of all wetlands in the Southeast has been altered to some degree (Noss and others 1995).

Unique or isolated wetlands have fared worst overall. Although the Southeastern United States has the highest diversity of carnivorous plants in the World, the habitat in which these plants occur has declined by approximately 97 percent. Reed wetlands, known as canebrakes, have been reduced by more than 98 percent (Mac and others 1998). Mountain bogs, especially those in the Southern Appalachians and Blue Ridge, are home to a great variety of unique native plant species. Although approximately 10 percent of these bogs remain, few are in fully functioning ecological condition (Mac and others 1998).

Pocosins, upland wetlands that occur on the Coastal Plain, have been reduced to about 20 percent of their original area (Mac and others 1998, Noss and others 1995). Similarly, only about 10 percent of the original Atlantic white-cedar forests, which require frequent, low-intensity fires and are typically only seasonally wet, are left (Noss and others 1995).

In the early 1600s, there were approximately 220 million acres of wetlands in the lower 48 States (Mitch and Gosselink 1993). Nationwide, over one-half of wetland acres have been converted to other uses. The degree of wetland loss has been less on the Coastal Plains, thanks in part to restoration and conservation activities that began in the 20^th century. Today, only 28 percent of Coastal Plain wetlands have been permanently converted (Noss and others 1995), but a significantly higher proportion have been impacted by human management and exotic plant species.

The degree of loss of wetlands varies widely among States within the South (table 2.1) and is complicated by the large-scale alterations of wetlands and hydrology conducted by humans. Countless acres of wetland have been drained either for agriculture, pasture, or urbanization, and countless other acres were lost during stream channelization, diking, or deforestation (Mac and others 1998, Mitch and Gosselink 1993, Noss and others 1995). The rate of wetland conversion was greatest (Mitch and Gosselink 1993) from the 1950s through the mid-1970s. Since the 1970s the States with the greatest rate of wetland loss nationwide are all in the South: Arkansas, Florida, Mississippi, North Carolina, and South Carolina (Mitch and Gosselink 1993).

The condition of the native plant communities discussed in this chapter is reflective of the condition of the majority of native plant communities in the South. In fact, it is exceptionally rare to find pristine plant communities. Even the most remote places have been affected by invasive exotic plants, introduced disease organisms, changes in community structure and function stemming from altered fire and hydrological regimes, and even changes in the local seed- and pollen-dispersing animals.