What is the most sustainable way to harvest a forest? A team led by USDA Forest Service scientists Katherine Elliott and Chelcy Miniat, along with Forest Service intern Andrea Medenblik, tries to answer this question. Data were analyzed from a long-term study looking at the biomass effects of partial-cutting versus clear-cutting in different watersheds in the southeastern US. Their results were published in the journal New Forests.
The study took place on two experimental watersheds in the Coweeta Hydrologic Laboratory in North Carolina, each harvested through partial-cutting or clear-cutting before 1978. In the study area, the forest was partially-cut – a practice also known as selective harvest – between 1900 and the 1950s. Clear-cutting, a complete harvest of all trees in an area, was popular from the 1960s to the 1980s.
The researchers compared biomass changes, the abundance of particular tree species, and overall tree diversity to determine which of the two harvesting methods resulted in a rebound closest to an unharvested watershed forest within the same region.
Their results showed that partial-cutting was a more sustainable harvesting method than clear-cutting in the Southern Appalachians. Over six decades, the partial-cutting watershed rebounded to close to the reference watershed in terms of all three metrics. In three decades, the clear-cut watershed recovered almost as much biomass but had lower diversity.
“These results were really rather surprising to us,” says Miniat, because of the outdated methodology used to harvest the watershed’s trees. In the mid-1940s, extensive soil disruption was among the long-lasting damages, as evidenced by physical disturbances of specific soil layers, root systems, and connections between fungi and plants. Light transmission onto the forest floor was also altered by this harvesting method, with a 30 percent decrease in tree cover.
Today, harvesting practices involve a specific type of partial-cutting, with the removal of trees similar to clear-cutting (60–80 percent of tree cover removed) but with minimal soil disruption.
The researchers suggest that changes in light exposure could be the dominant factor in determining a forest’s ability to return to ‘normal’ conditions, rather than soil disturbance in these forests.
These analyzed forests, however, are not stagnant environments that return to one resting equilibrium. While oaks and hickories previously dominated the landscape, different species are beginning to dominate modern forests, such as red maple and tulip poplar. These latter species are especially concerning as they use more water than oaks, and put increased strain on water supplies from these forests. While gradual, these changes can be significantly accelerated by clear-cutting rather than partial-cutting, as observed in these watersheds.
With multiple ecological and economic resources dependent on these forests’ state, it is integral to implement the best harvesting techniques. Although there isn’t one perfect method, it is clear that past partial-cutting treatments resulted in better biomass conditions and diversity than past clear-cutting. “With long-term studies like this, we all have an opportunity to learn from past management practices to guide future practices,” says Miniat.
This publication was one of lead author Dr. Katherine Elliott’s many on Southern Appalachian forest dynamics. She retired on June 30 from an almost thirty-year career with the USDA Forest Service. Elliott worked at the Coweeta Hydrologic Laboratory, where this study took place, for her entire tenure as a Forest Service research ecologist.
“She’s an inspiration to many different people, especially women in science,” says Miniat. “She was an early mentor to Medenblik, who was a summer intern on this project. She has gone on to obtain her master’s and become a research scientist with the U.S. Geological Survey.”
With the help of this study and future studies by scientists inspired by Elliott’s career work, the most sustainable practices will hopefully guide future policy and harvests in the Southern Appalachians.
For more information, email Chelcy Miniat at firstname.lastname@example.org.