Ecological dynamics

The Dry Sandy Backslope Woodland site is composed of woodland vegetation with a canopy dominated by longleaf pine found on deep sands of dry uplands in the Carolina and Georgia Sand Hills (MLRA 137). These sites are prone to wildland fire. The natural fire regime, ignited by lightning, was probably as frequent as every few years (fire return interval = 2-3 years). Other fires were ignited by humans. Prior to the construction of roads, wildland fires may have burned extensively (thousands of acres). While most lightning in this area is associated with rain, lightning combined with high winds can start wildland fires. Today, prescribed fire can be used by land management agencies to restore and/or maintain the site.

The ecological dynamics of the Dry Sandy Backslope Woodland are fire-dependent. There are two sources of fuel for the surface fires typical of the site. These are longleaf pine needles and the native herbaceous ground cover, especially native grasses such as wiregrass (Aristida stricta and A. beyrichiana). Naturally functioning sites need both fuel sources to adequately carry the frequent fires that are needed to maintain the site. The loss of either the longleaf pine trees or the native herbaceous ground cover can lead to less frequent surface fires, since fine fuels are reduced. Prolonged fire suppression alters the structure and composition of the site by driving succession toward hardwood dominated communities. Because of the steeper slopes associated with this ecological site, there may be instances of hardwood communities occurring on different aspects.

During the 19th century, longleaf pine declined as a result of turpentine extraction methods which damaged the trees and left them more susceptible to further damage from fire. Longleaf pine timber was coveted for its strength and durability, and many areas were nearly completely depleted of longleaf pine in the early 20th century (Frost and Langley, 2008). The timber industry moved on to other areas where large longleaf pine trees remained, continuing the cycle of tree loss. Longleaf pine is slower growing than loblolly and slash pine and will not regenerate as easily without fire. Many areas once native to longleaf pine became dominated by loblolly pine and hardwood trees as wildland fires were controlled in the middle of the 20th century. In recent decades land managers have become skilled at managing longleaf pine woodlands, and the value of longleaf pine forest products has gained more attention. The special qualities of longleaf pine woodlands are now recognized for their beauty and high biological diversity. Numerous rare plants and animals persist in the Dry Sandy Upland Woodland habitat, especially on the larger public lands, such as military installations and gamelands.

Restoration

Of the remaining areas of longleaf pine ecosystems, only about half are managed, leading to substantial alterations in ecosystem structure and composition (Outcalt, 2000). Pre-settlement fire regimes were typified by short fire-return intervals (FRI = 2–3 years), low-intensity surface fires ignited by lightning, and late Holocene Native Americans (Christensen, 1981). Fire suppression transforms these once open savanna–woodland ecosystems into closed canopy forests, with reduced floral and faunal species richness, as well as heavy accumulations of surface fuels. In some cases, changes from one state to another are reversible, but the return path is different from the path taken in the original change. Therefore, a thorough evaluation of reversibility is necessary before adopting a program of rehabilitation. For instance, a case study by Groffman and others (2006) revealed re-introduction of fire to areas that were suppressed was not effective in reversing the loss of longleaf pine because changes in the distribution of the vegetation lost the ability to transmit fire. Therefore more aggressive management of fire and competing vegetation may be required. General techniques and strategies for restoring upland ecosystems for longleaf pine related to this ecological site are discussed in the individual state and pathway narratives. On- site evaluations are required in order to develop specific recommendations and management prescriptions for desired states.

Prescribed fire is the most common management practice for restoring and maintaining longleaf pine ecosystems. The longleaf pine canopy and wiregrass in the understory function together as keystone species that facilitate but are resistant to fire (Platt et. al., 1988). Growing season burns, especially if frequent, can top kill and remove invading hardwoods effectively while winter fires are best suited for the reduction of hazardous fuels. Seasonality of fires will have varying results, depending on the desired outcome (i.e., vegetation control, seed bed preparation, wildlife forage, etc.) and the specific set of environmental conditions that govern the site.

Chemical control of vegetation, such as the selective application of herbicides, can accelerate the restoration process, especially where the ecosystem is degraded by oak invasion. For instance, low rates of hexazinone application have shown to be very effective in decreasing midstory hardwoods with little or no short-term reduction of understory grasses and forbs on sandhills sites (Brockway et. al., 1998). Other herbicides used in forest management include Velpar L and Pronone 10G. However, the rate of restoration can be significantly more rapid when chemical application is combined with prescribed burning (Boyer, 1991).

Mechanical drum shredders can control large mid-story vegetation. This is a recommended method to accomplish restoration of severely degraded longleaf pine forests. However, the use of mechanical control methods are often expensive, and their effectiveness can be short-lived because brush recovers rapidly in the region (Haywood et al., 2004). In addition, mechanical methods can destroy residual native ground cover propagules. If the management goal is to maintain intact native ground cover, other management options may be more suitable. In most instances, a combination of management practices is recommended in addition to the planting and monitoring of native vegetation.

State and Transition Model

A State and Transition Model for the Dry Sandy Upland Woodland Ecological Site (DSUW) follows this narrative. Thorough descriptions of each state, plant community phase, and transition and restoration pathways are found in the appropriate State narratives. This model is based on available experimental research, field observations, professional consensus, and interpretations. It is likely to change as knowledge increases.

Plant communities will differ across the MLRA because of the naturally occurring variability in weather, soils, and aspect. The reference plant community (state 1) is not necessarily the management goal. Because landowners have different management goals, the STM outlines methods used to transition to or restore a specific community. Biological processes on this site are complex. Therefore, representative values are presented in a land management context. The species lists are representative and are not complete botanical descriptions of all species occurring, or potentially occurring, on this site. The lists are not intended to cover the full range of botanical potential and site conditions or vegetative response to the conditions.

The following diagram suggests some pathways that the vegetation on this site might take. There may be other states not shown on the diagram. This information is intended to show what might happen in a given set of circumstances. It does not mean the pathway would proceed the same way in every instance. Local professional guidance should always be sought before pursuing a treatment scenario.