White oak (Quercus alba) is an incredibly important species, anchoring ecosystems and economies. Current demand for white oak is surging due to its use in making barrels to support a growing spirits industry. Thus, there’s a real need understand the best tools to promote and sustain white oak in forests to support both economic and ecosystem benefits that the species provides.
USDA Forest Service research forester Callie Schweitzer has spent her career studying upland hardwood forests. “Oak regeneration in the East has been an issue for at least 60 years,” says Schweitzer. “We have plenty of white oak and plenty of acorns. The problem is recruiting younger oaks into more competitive positions to ensure oak dominated stands in the future.”
Why is there a lack of younger oak? One answer is the absence of prescribed fire over the years leading to changes in site conditions like moisture and shade. The changes favor species that compete with oak, like red maple (Acer rubrum). In these conditions, fewer young oak grow into large trees.
Oaks have adaptations that allow them to respond to fire, such as storing carbohydrates in their roots that allows for re-sprouting if top-killed by fire. So forest managers frequently include prescribed fire in oak forest restoration plans. Thinning to improve understory light conditions is another tool that managers use.
“A big question is how to disturb in a way that stimulates oak into competitive positions, without stimulating the growth of competitors,” says Schweitzer.
Schweitzer collaborated with fellow research forester Daniel Dey of the Northern Research Station and colleague Yong Wang from Alabama A&M University to see how different combinations of thinning and fire affected white oak. The study was published in the journal Forest Science.
The study was set up on the William B. Bankhead National Forest in northcentral Alabama. They applied thinning treatments — heavy, light, and a no thin control – in combination with prescribed fire treatments – dormant season burns of none, one, or three fires. The researchers identified, counted, and measured seedlings, sprouts, saplings, and mature trees pre-treatment and again after the final burn (seven growing seasons later). They also assessed indicators of tree injury from fire.
Three fires increased the density of white oak seedlings, regardless of thinning treatment. Thinning with one fire resulted in the highest densities of white oak saplings. Thinned and burned stands had larger white oak seedling sprouts than those thinned with no burns. Results also suggested that risks to tree value from fire damage may be offset by gains in oak regeneration success.
But fire benefited red maple too. It is the dominant competitor in all treatments and is currently positioned to dominate if not controlled.
These results suggest that fire may not be the answer at this site. “Repeated prescribed burning is keeping the oaks and their most prolific competitor in a reproductive fire trap,” says Schweitzer.
Results also suggest that more intense thinning may be needed to enhance the understory light environment enough to promote oak. “Thinning to 75 percent was not heavy enough,” adds Schweitzer.
Listen to a brief audio clip by author Callie Schweitzer describing this publication. • Text Transcript
A similar study by Schweitzer and colleagues shows promise for oak under herbicide and heavier thinning treatments, but challenges remained with hardwood competitors.
Schweitzer emphasizes the importance of keeping studies like this going and adapting them as needed. “If we don’t do applied management we are not going to have stands that provide us with the benefits we want. If you don’t manage them, they are going to go in a direction that doesn’t meet societal goals.”
Continued research on oak regeneration will provide managers with tools to maintain this vital component of U.S. forests.
Read the full text of the article.
For more information, email Callie Schweitzer at callie.schweitzer@usda.gov.