After a series of record-breaking forest megafires in the western U.S., Penn State geographers, like Jamie Peeler, worked to develop guidelines to help forest managers determine where to replant trees and expect natural regrowth.
Peeler, a recent Penn State doctoral graduate, NatureNet science fellow for The Nature Conservancy and co-author of the paper that includes the guidelines, said, “We are seeing more and more forest fire activity, and forests are having a much harder time recovering.”
“In 2020, California faced six of its 10 largest fires on record, while Colorado fought its largest, second-largest and third-largest fires in modern history,” the researchers reported in their paper. “Oregon watched 900,000 acres burn in 72 hours — nearly double the acreage that burns in a typical year.”
Forest recovery is complex because individual forest fires don’t burn uniformly across a forest environment, according to the paper.
Additionally, the researchers said tree regeneration is governed by landscape factors like seed sources and terrain — as well as local factors like water availability and soil nutrients, which make tree replacement difficult, the paper said.
The researchers sampled landscape and local variables on 71 plots near Jackson, Wyoming. Using computer analysis, they examined which landscape and local variables impacted post-fire recovery.
Across post-fire plots, they found landscape factors like seed source area — the percentage of live trees within a 100 meter radius — will allow managers to determine the existence and density of tree species. However, thresholds for achieving tree existence and tree density differed.
Tree density “is an important metric for predicting wildlife habitat,” Peeler said.
Along with seed sources, the researchers found terrain influenced critical landscape processes associated with tree regrowth after a fire.
“Your position in the terrain is really important,” Peeler said. “You could have a suitable amount of living seed sources around you, but if you’re high up on a ridge — so above all of the surviving surrounding trees — your potential to recover is lower than if you were in the valley and likely below those surviving trees.”
Erica Smithwick, distinguished Penn State professor of geography, associate director of Penn State’s Institute of Energy and the Environment and co-author of the paper, said forest management agencies are thinking about proactive restocking tools because “we may not have time to wait for the system to naturally recover.”
“Managers have this need to maintain a certain stocking density in their forest,” Smithwick said, “and the question is — where?”
Smithwick said forest managers have “limited resources,” which makes prioritizing where to implement forest restoration practices difficult.
“And not all landscapes are the same,” Smithwick said. “These landscapes are very complex, very heterogeneous.”
Diane Abendroth, an interagency fire ecologist for the Bridger-Teton National Forest and Grand Teton National Park, helped Peeler and Smithwick design the study.
“From a fire manager’s side,” Abendroth said, “we need to know, ‘How long does it take for the different kinds of trees to [grow] back [after a fire], and what spatial patterns they [grow] back in?’”
Fire managers need to better understand how fires impact landscape ecology — including “plants, habitats and sometimes soils,” Abendroth said, and where to plant seedlings when “more and larger fires occur in the future.”
Abendroth also said there’s a great need for managers to develop a better understanding of where to concentrate regeneration efforts — especially in response to climate change, which she considers to be “the most challenging aspect of her work.”
“All of the assumptions we made about fires’ role on the landscape are changing,” Abendroth said, “and we need to be adaptable to that.”
Smithwick said the “weather conditions” that created the Yellowstone megafires of 1988, which “consumed up to 40% of the national park,” are likely to become “much more common in the future.”
Her prior work showed these “[mega]fires are much more probable,” she said.
“We’re likely to have fire return intervals that are maybe on the order of every 30 years or so,” Smithwick said.
Forest regeneration is critical because forests supply important societal services, such as the capturing and storing of carbon dioxide, as well as maintaining wildlife habitats, water quality and recreational activities, according to the researchers.
Smithwick said people need to start thinking differently about how to “support nature's own ability to recover.”
“I care about this because I want to be able to bring my children to these landscapes and show them the kinds of landscapes I first fell in love with,” Smithwick said, “and those landscapes aren’t going to be there much longer at this rate.”