University of Vermont

Vermont Quarterly

Wisdom of Old Growth

Professor Bill Keeton in an old growth forest.

DEPARTMENTS/
NEW KNOWLEDGE

Wisdom of Old Growth

Study explores forest management and carbon storage

Photograph and story by Joshua Brown

Bill Keeton points ahead in the forest. “There’s one of the tip-up mounds we made,” he says, walking over to a ten-foot-high wall of torn tree roots that have yanked up soil and rocks, leaving a shallow hole behind. “Bears like to den under these in the winter,” he says, “and winter wrens make nests here.” Fourteen years ago, he directed a team of foresters to harvest some of the trees on this hillside at UVM’s 485-acre Jericho Research Forest, including hemlock, maple, and commercially valuable red oak. But some of the biggest trees were left uncut—and others, like this one, were simply pushed over with a skidder, and left on the ground. Now the decaying trunk stretches across a sunny patch in the middle of the cool woods. “We’re mimicking natural disturbance, like wind throw,” he says. “See that nice big tree up there? We’ve let in a lot of light, released its crown to really grow.” On top of the tip-up mound, Keeton points out four species of ferns, blackberry bushes, elderberry, and yellow birch saplings all reaching toward the sun. 

For nearly two decades, Keeton, a professor of forest ecology and forestry, has been running experiments here and on the side of Mount Mansfield. These studies show how imitating key characteristics of old-growth forests in managed timberland can increase biodiversity (including notable increases in mushrooms, herbaceous plants, and amphibians), enhance the ecosystem services that forests provide to people (like clean water), and, ultimately, restore old-growth forests—“a vastly underrepresented forest type in the Northern Forest,” Keeton says, due to the lingering effects of forest clearing in the eighteenth and nineteenth centuries.

Now his team’s newest results point to another benefit: imitating old-growth forests enhances carbon storage in managed forestland far better than conventional forestry techniques.

As the planet warms, carbon markets are getting hot, too. Forest landowners have been looking for ways to enter these markets, making money from their commercial timberland not just by selling logs—but also by demonstrating that their land is absorbing climate-warming carbon dioxide from the air. The more carbon an acre of trees holds, the more valuable it will be in these new carbon markets.

But there’s a vexing question: what forestry techniques do the best job of maximizing carbon storage in trees and soil—while still allowing landowners to provide habitat for wildlife and harvest timber for profitable sale?

NEW OLD GROWTH

Keeton calls his approach “structural complexity enhancement,” or SCE. It’s a suite of forestry techniques designed to imitate the ingenious complexity of old forests—with trees of many ages and heights, including old and very large ones, a rich layer of downed logs and woody debris on the forest floor, and a patchwork of small gaps that wind storms and other natural disturbances leave behind. 

Using this innovative style of forestry, Keeton and his students report that they can maintain high levels of carbon storage on managed timberland: A decade after harvesting, carbon storage in the experimental forestry plots was just fifteen percent less than what would accumulate over time in forests that were not logged at all. In contrast, their study shows that conventionally managed timberland holds about forty-five percent less carbon than uncut forests.

“This approach can let landowners restore old-growth forest habitats, fight climate change, and make a moderate amount of money—all at the same time,” says Keeton, who co-led the new study with former UVM student Sarah Ford ’03 G’15. Their results were published this spring in the journal Ecosphere.

“There are many goals and options that landowners have for their forests,” says Keeton. “This is a great new tool for foresters and landowners to have in their tool box.”

The scientists were very surprised the growth rates of trees in their experimental forests exceeded the areas managed with conventional techniques. “This overturns previous dogma that more heavily thinned areas would have faster growth that would sequester carbon more rapidly than old trees,” Keeton says. And in one key pool of stored carbon—coarse woody material lying on the ground—the new technique led to more carbon being captured than even the control plots where no forestry work was done.

CONSERVATION CONCERNS

In other words, for conservation-minded land owners, like land trusts or forest preserves, Keeton’s SCE approach could lead to more carbon storage, and faster creation of old-growth types of habitats, than doing nothing at all.

“It’s possible to accelerate the recovery of old growth in the Northern Forest,” says Keeton, who co-directs the Forestry Program in UVM’s Rubenstein School of Environment and Natural Resources and serves as a fellow in the university’s new Gund Institute for Environment.

As the climate warms, that goal becomes increasingly urgent—and the definition of old growth itself becomes increasingly complex. With warmer temperatures and many new invasive pests, “the baseline is shifting,” Keeton says. Restoring old growth to the Northern Forest “does not mean going back to the forests we had four hundred years ago,” he explains. Instead, he sees old growth restoration as a form of adaptation for the future. The characteristics of old forests—“like their structural complexity, closed canopies, high levels of biodiversity, mixed-age trees, and microclimates,” Keeton says—can give land resilience against drought, higher temperatures, diseases, storms, and rapid ecosystem changes.

“We’ll need more old growth in the future,” Bill Keeton says.

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