Scientists studying forest density in the Sierra Nevada have found that trees there were scarcer but physically larger in 1911 than in 2011, meaning “resilient” forests might be remarkably thin by today’s standards.
“Our findings suggest forests need to be treated more intensively than is often done when just reducing fuels, particularly greater reductions in density,” Malcolm North, a professor at the University of California–Davis, and lead author of the study, told The Epoch Times in an email. He said the findings could be applicable to many forests across the Western United States.
The study, published in the journal Forest Ecology and Management, comes at a time when environmental “resilience” has become a hot topic, including among lawmakers.
The bipartisan infrastructure bill passed in November 2021 allocated billions of taxpayer dollars to various forms of “resilience” and “resiliency” efforts, including a reported $50 billion for climate resilience and weatherization, according to CNBC.
Forest resiliency has started to attract attention and capital as well. In October 2021, the nonprofit World Resources Institute, the U.S. Forest Service, and several other organizations launched one of the first Forest Resilience Bonds as a means of funding the protection and post-fire restoration of California’s Tahoe National Forest.
Recent devastating wildfires in California have also brought renewed attention to the complex relationship between forest fires and forest health.
The blame for those fires has been pinned on a variety of factors. California Gov. Gavin Newsom has attributed them to climate change as well as poor forest management practices.
North and his co-authors argue that frequent forest fires, common in the Sierra Nevada and other regions before people started suppressing them, helped to remove competition among trees, yielding more vigorous individual specimens and more resilient forests.
The researchers defined resilience in terms of a forest’s capacity to persist or thrive when under pressure from insects, fire, drought, or other characteristic stressors.
“The term resilience is useful for communicating across disciplines and developing shared goals, but in that usage isn’t concrete enough to have scientific rigor or to be operationalized. The paper develops a definition that is specific to dry western frequent-fire forests, and once grounded in that context, becomes more concrete and can be assessed using stand density index,” North wrote.
Stand density index (SDI) allows foresters to assess how well-stocked a forest is; forests with higher SDIs are denser.
The scientists calculated the SDIs of forests from 1911 using data gathered through a pair of timber inventories taken that year. Their 2011 data came from a dataset known as F3, which relies on U.S. Forest Service forest inventory and analysis (FIA) data and satellite data, along with the forest vegetation simulator.
The scientists emphasize that their investigation was correlational and observational, not a controlled experiment.
Many commercial foresters have come to similar conclusions about forest density and the role of fire.
“Healthy, wildfire-resilient, and late-successional forests have adequate space between trees. When forests are overly dense—that is, ‘overstocked’ and filled with too many trees in a given area—the trees in that forest have to compete for more limited resources,” a spokesperson for the National Association of State Foresters told The Epoch Times in an email.
“Prescribed fire is an invaluable tool for forest and habitat management.”
A spokesperson for the Federal Forest Resource Coalition wrote as part of a statement on the Forest Service’s new 10-Year Strategy on Wildfires: “We cannot reverse the current pattern of loss and devastation solely with drip torches or by clearing brush near homes. We must manage forested watersheds to restore them to health.”
In their paper, North and his co-authors wrote that their findings suggest much lower SDIs than even many foresters advocate: “Instead of 35 percent representing a minimum stocking level, our analysis suggests that it may more appropriately represent a maximum stocking level.”
North told The Epoch Times that small, commercially nonviable trees could be removed through a mechanical thinning process involving chainsaws.
“The small trees could go to biomass facilities that generate electricity and/or heat, but there aren’t many of those plants in the western U.S., and the economics limit the haul radius to no more than about 50 meters (54.7 yards) from a facility. This would also be accomplished with both prescribed and managed wildfire.”
Not all scientists agree with North on the danger of overstocking forests.
Ecologist George Wuerthner has written about tree density before, arguing that foresters’ concerns about it have more to do with the economics of the wood and paper sector than with ecosystem health.
“Many fire researchers believe that many forest stands were always dense,” Wuerthner told The Epoch Times in an email. He referred to a 2014 study based on Forest Inventory and Analysis data from the U.S. Forest Service as well as other data; the authors concluded that unlogged mixed-conifer and ponderosa pine forests in the American West were very dense a century or more ago.
He also cited the work of Robert W. Cermak, who has turned to 19th-century diaries from California to argue that forests in the area were quite dense rather than open.
“Forest health has been defined by the timber industry and their allies in forestry schools. These entities prefer ‘green forest’ because that makes the best trees for logging,” Wuerthner wrote.
According to North, Wuerthner’s view is a fringe position.
“About 98 percent of fire and forest scientists do not share this point of view and feel it is agenda-driven since it does not square with almost all of the data that has been collected over the last 100+ years,” he wrote.