About half of southern forests are a mix of oaks and pines growing side by side. In the past, getting rid of either the oaks or the pines had been a common management goal.
“Pine plantations – stands with no oaks – have become one of the most recognizable symbols of forest management,” says John Willis, a USDA Forest Service researcher.
Managing oaks and pines together is re-emerging as a goal for many landowners. In some areas, pine plantations are not profitable. And some landowners may want the ecosystem services of a mixed stand.
In a recent study published in the journal Forests, Willis and his colleagues discuss mixed stands as a reasonable alternative to pine plantations or exclusively managing for hardwoods.
Mixed stands are less susceptible to pests such as the southern pine beetle. They may be able to withstand high winds better – loblolly pine has shallow roots and is prone to toppling. And they could be more productive.
“On some sites, you can grow pine-hardwood mixes at comparable rates to pine monocultures,” says Willis. “Cherrybark oak-loblolly pine mixtures and sweetgum-loblolly mixtures can grow together, with only slightly lower productivity than a loblolly plantation. Shortleaf pine is not quite as productive as loblolly pine but may be a better pine option in mixed stands.”
Over the decades, more and more acres have been planted with pine. But in general, pine prices have fallen over the last decade. However, hardwood sawtimber prices have gone up. “Having a mixed stand can give landowners more flexibility,” says Willis.
“There’s not one type of mixed stand,” says Willis. “There are lots of types, and they can vary depending on the legacy of past land use, species composition, seedbank, and other factors.”
In upland hardwoods some landowners want to add an oak component to a pine plantation. But oak regeneration – especially on fertile sites – has been faltering for decades. Thinning and prescribed fire will likely be necessary to restore oak. Researchers with the Upland Hardwood Ecology and Management group have developed a huge body of knowledge about oak regeneration, and research on novel management strategies such as femelschlag, as well as other silvicultural methods, continues.
In many forests, faster growing trees such as red maple overtake the oaks. After a red maple tree is cut down, the stump also sprouts prolifically, as Tara Keyser and others showed in a study of 19 upland hardwood species and their ability to stump sprout.
“Sprouting is going to be very important in terms of mixed-stand management,” says Willis. “It will either be your friend or your enemy.”
On dry and sandy sites, the presence of oak trees can help longleaf pine seedlings survive.
In a separate study, Willis and colleagues monitored longleaf pine seedlings for two years. “Seedling growth was not significantly impacted by the presence of a midstory,” says Willis. “Collectively, this research suggests that a hardwood midstory can help longleaf seedlings survive – especially on dry sites.” Willis shared the findings at the 20th Biennial Southern Silvicultural Research Conference.
Mixed-stand management is not a new idea. Researchers from the University of Tennessee, Virginia Polytechnic Institute and State University, and many other organizations have contributed to the field.
In 1989, more than 200 land managers and researchers gathered for a symposium on the management and ecology of pine-hardwood forests. The proceedings from this symposium, which included 34 papers in four categories, are available as a General Technical Report.
More recently, mixed stand management was discussed during the Southern Pine Module, which brought experts from across the Forest Service together with experts from the University of Arkansas and the Shortleaf Pine Initiative. Recordings from this workshop are available [internal link].
At the Upland Hardwood Silviculture Workshop, mixed-stand management was also a topic – possibly for the first time since the workshops began in 1992, as research forester Stacy Clark pointed out. All the presentations from this workshop are available on the Bent Creek Experimental Forest website.
“Mixed-stand management will not be the optimal strategy in all scenarios,” says Willis. “But is an alternative strategy for land managers to consider.”
For more information, email John Willis at email@example.com.