Understory Restoration in Longleaf Pine Ecosystems

Longleaf pine stand in the Croatan National Forest, North Carolina. Photo by David McAdoo, Creative Commons.
Longleaf pine stand in the Croatan National Forest, North Carolina. Photo by David McAdoo, Creative Commons.

Longleaf pine trees once rose to the sky on more than 90 million acres across the Southeast, towering over grasses and flowers and providing habitat for many animals that are now rare. Less than 3 million acres of these forests remain, but returning degraded ecosystems to longleaf pine forests is a priority for many managers and organizations.

U.S. Forest Service scientist Joan Walker and her colleagues developed a roadmap for restoring these forests, especially the understory plant communities. Walker, a plant ecologist at the Forest Service Southern Research Station Restoring Longleaf Pine Ecosystems unit, co-authored a study that quantified and evaluated a reference model for use in restoring southeastern U.S. longleaf pine woodland understory plant communities. The study was led by Lars Brudvig, a professor at Michigan State University, and published in an article in PLoS ONE.

Walker and her colleagues developed and quantified local and regional models of longleaf pine ecosystems. The models used information from 232 longleaf pine woodland sites in longleaf pine’s historical range. There were three study areas – Fort Bragg, North Carolina; Fort Stewart, Georgia; and the Savannah River Site, South Carolina. The models showed how previous land use, fire frequency, and canopy overstory affected grasses and flowers on the forest floor.  The scientists found that all the suspected degradation factors were important, but the effects varied among the study locations.

In the regional model, fire frequency and land use history were the most important factors affecting longleaf pine forests and their understory herbaceous communities. Like much of the longleaf pine region, the study locations were historically fragmented by agriculture. Areas with a history of agricultural use and low fire frequency were the most degraded, while historically forested sites were more similar to each other, and to the reference sites. The importance of land use legacies is becoming clear, and the study shows that multiple drivers of ecosystem degradation – including land use histories – can be quantitatively incorporated into ecological reference models.

The researchers also developed location-specific models for each study area, and found that there were many variations between regional and local models. For the Savannah River Site, the three main factors affecting understory communities were the same identified in the regional model – fire, land use history, and the size of trees – although the importance of each factor differed. The other two sites differed even more from the regional model. On Fort Bragg, land use history explained all the changes in understory plant communities, while on Fort Stewart, soil characteristics were the most important factor.

The remaining challenge is to determine how to best restore longleaf pine understory communities once patterns of degradation have been assessed. Based on the model, thinning overstory trees in some areas may promote understory diversity, while replanting native understory species may be more helpful in others. Wiregrass is one of the species that may need to be replanted in some areas, and Walker and her colleagues at Clemson University are currently growing wiregrass in common gardens. The grass will eventually be used in restoration efforts and future studies.

The model lets managers broadly infer the degradation status of longleaf pine understory communities in the study region. Additionally, since the information used to construct the models is often readily available, the framework can be used to develop local reference models for other areas. This flexibility means the approach can also be applicable to degraded ecosystems across the globe, since information about other suspected drivers of ecosystem degradation can be added to the model.

Read the full text of the article.                                                                                                                     

For more information, email Joan Walker at joanwalker@fs.fed.us

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