Research shows that resilient, frequently burned forests have fewer trees
UNIVERSITY OF CALIFORNIA – DAVIS
CREDIT: PACIFIC FOREST SERVICES SOUTHWEST, USDA
What does the “resilient” forest in California’s Sierra Nevada look like? According to a study of frequently burned forests from the University of California, Davis, the number of trees is less than we are used to seeing.
More than a century ago, the Sierra Nevada forest faced almost no competition from neighboring trees for resources. The density of trees in the late 1800s would astound most Californians today. Due to fire suppression, trees in current forests live with six to seven times more trees than their ancestors did – competing for less water in drier and hotter conditions.
Research, published in a magazine Ecosystem and forest management, suggesting that low density stands that eliminate much of the tree competition are key to creating forests that are resistant to many of the stressors of severe wildfire, drought, beetles and climate change.
This approach would be a significant departure from current management strategies, which use competition between trees to direct forest development.
Define ‘resilience’
But first, research Ask: What does “resilient” mean? Increasingly appearing in management plans, the term is vague and difficult to quantify. The authors developed this operational definition: “Resilience is a measure of a forest’s ability to adapt to a range of stresses and reflects the functional integrity of an ecosystem.”
They also found that a popular forestry tool – the Standing Density Index, or SDI – is effective for assessing forest resilience.
“Forests,” said lead author Malcolm North, an associate professor of forest ecology in the UC Davis Department of Plant Science and a research ecologist with the US Forest Service, Southwest Pacific Research Station. restore responses to multiple types of stressors, not just one.” “’Resistance’ is about surviving a specific stress, such as fire – but there is much more going on in these forests, especially with the stress of climate change. .”
Competitive nature
For the fire-adapted forests of the Sierra, managing resilience requires drastic reductions in density – possibly up to 80% of the trees, in some cases.
“Treatments to restore resilience in today’s forests would need to be much more intensive, then focus on reducing it,” said Scott Stephens of UC Berkeley, a co-author of the paper. less fuel.
The study compared large-scale historical and contemporary data sets and forest conditions in the southern and central Sierra Nevada, from the Sequoia National Forest to the Stanislaus National Forest. It found that between 1911 and 2011, tree density increased six to seven times while the average tree size halved.
A century ago, stand density and competition were both low. More than three-quarters of the stands have little or no competition for stunted growth and reduced vigor. In contrast, nearly all – 82%-95% – of modern regularly burned forests are considered “fully competitive”.
Research shows that forests with very low tree density are better able to withstand the complex threats of fire, drought and other climate stressors while maintaining healthy water quality. health, wildlife habitat and other natural interests. Forests burned by severe fires or killed by drought will deprive those ecosystem services of services.
Wake up
The authors say the 2012-2016 drought, in which nearly 150 million trees died as a result of the drought, was a wake-up call to the forestry community that different approaches are needed to help forests cope with the drought. faces many threats, not just serious ones. Forest fires.
The shift away from competitive management of forests and towards de-competition could allow a small number of forests to grow and be more resilient.
“People are used to the type of high density forest we live in,” says North. “Most people would be surprised to see what these forests used to look like when frequent surface fires left them at very low densities. But removing the smaller trees and letting those that can weather fire and drought leave a pretty impressive forest. It means creating very open conditions with little competition between plants. But there is a lot of historical data to back this up.”
“We think highly resilient forests could be created, but it would require a drastic reduction in tree density until that is,” said Brandon Collins of UC Berkeley, another co-author of the paper. there is little or no competition”. “Doing this will allow these forests to adapt to future climates.”
Other co-authors include Ryan Tompkins of UC Cooperative Extension, and Alexis Bernal and Robert York of UC Berkeley.
The study was funded by the National Parks Administration for the Western Pacific, the US Forest Service’s Pacific Southwest Research Station, the US Joint Fire Science Program, and the Department of Agriculture and Natural Resources. UC industry.
JOURNEYS
Ecosystem and forest management
DOI
10.1016 / j.foreco.2021.120004
RESEARCH METHODS
Image analysis
ARTICLE TITLE
Operational resilience in the frequently burned forests of the western US
ARTICLE PUBLICATION DATE
18-Jan-2022
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