Northern red oak: a contender or a member?
Northern red oak in the Appalachians
Grows to be stately at high elevations
But is there regen? And what makes it thrive?
Harvest makes light to keep it alive
But fire suppression helps mesophytes reign
A little control may help red oak sustain
Site treatment with fire and some herbicide
May help each species to its place abide
Or perhaps success is an evolving bar
Functional diversity may now be the star.
The lack of oak regeneration in the eastern United States is not a new concern. USDA Forest Service scientist Tara Keyser recently published results of a legacy study initiated by her predecessor David Loftis (retired). The study provides new insight into the understudied high elevation northern red oak (Quercus rubra) forest community and the factors that affect regeneration success.
Regeneration is the process of the smallest trees of the forest – seedlings and saplings – being released and growing into the canopy to become the dominant species in a forest community.
Northern red oak ranges from Mississippi to Maine and is valued for timber, as wildlife food source, and for its beauty. These high elevation northern red oak stands in the southern Appalachian Mountains of western North Carolina make up the transition zone between the low elevation temperate mixed oak forest and the high elevation spruce-fir (Picea-Abies) forests.
Few studies have looked at the impact of disturbance, including timber harvest, in high elevation northern red oak stands. In the mid-1990s Loftis implemented a study with four harvest types: a group selection gap which left no trees, a shelterwood that left few trees, a shelterwood that left a lot of trees, and a control which left all the trees.
Plots were measured before treatment, and 4 and 22 years after treatment. The good news is the number of regenerating northern red oaks increased in all harvested treatments, except control plots where sapling-sized northern red oak declined from 22% to 0% after 22 years. Clearly northern red oak benefited from the increased light from harvest treatments.
The increased light, however, also encouraged the growth of other species, especially mesophytic, shade-tolerant and intolerant ones. “It was interesting that this study occurred at an elevation where tulip poplar is not abundant or competitive. However, species like red maple were strong competitors,” noted Keyser.
There are many tools in the toolbox to regenerate oak. Using prescribed fire well in advance of harvest treatment may give oaks an advantage. After harvest, herbicides can slow the growth of red maple and other competitors to give oak a stem up.
“This study confirms what we know about oak silviculture,” says Keyser. “For oak to be successful it must be present in stands. And it must be of substantial size to compete with mesic species.”
In the last two decades the focus of silviculture has changed from efficiently growing a single species for timber output to one that looks at systems more holistically.
“If we look at the current overstory composition as our metric for success we will always fail,” says Keyser. “The disturbance regimes that created this forest are so complex and we have altered the frequency and severity of the various elements of the disturbance regime.” For example, the removal of American chestnut from the overstory is a huge composition change.
“We are now trying to restore species composition in terms of their functional role. We are thinking about ecological memory, heterogeneity versus homogeneity. We are looking at disturbance as an integral part of ecosystems and restoring ecosystem processes instead of just focusing on individual species,” says Keyser.
Read the full text of the article.
For more information, email Tara Keyser at tara.keyser@usda.gov.