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Trapped forests lose their strength


1875 City of Boulder Reservoir, illustrated by J.B. Sturtevant (“Rocky Mountain Joe”). Credit: Carnegie Library of Local History, Boulder Public Library

The US Senate candidate in Georgia has slammed the Biden administration’s $3.5 trillion inflation-reducing law, which earmarks funding for planting and protecting trees.

“They keep trying to trick you that they’re helping you. But they’re not. Because a lot of the money goes into the trees,” said GOP candidate Herschel Walker as he stumbled into a fundraiser. “We have enough trees – don’t we have enough trees here?”

2015 study in nature It is estimated that there are 3 trillion trees on the planet. And whether that was “enough” or not, the survey also found that “the global number of trees has declined by about 46% since the beginning of human civilization.”

And according to a University of Colorado Boulder scientist who has been monitoring the health and population of trees in upland Colorado for more than four decades, climate changes in temperature and drought have only tripled tree mortality rates in the past two decades. , but also greatly undermined tree renewal rates.

And this is important.

“If we lose forest cover, we lose a variety of ecosystem services,” says Tom Veblen, Distinguished Professor Emeritus of Geography, who has been tracking changes in thousands of trees in Newt Ridge west of Boulder since 1982.

Trapped forests lose their strength

Tom Veblen, Distinguished Professor Emeritus of Geography, is in roughly the same spot as the 1875 photograph above. Credit: Glenn Asakawa.

Decreased tree cover leads to watershed damage with increased debris flow and flooding, and habitat loss for some species. Perhaps most devastating is the loss of “above-ground biomass” which removes a vital source of carbon storage, adding to climate change.

“In most models of simulations of ecosystem impacts of climate change… trees grow back after fires. But we don’t see that as documented for mountain forests in Colorado,” says Veblen. This results in “one of those rather unpredictable and nasty positive feedback loops that accelerate climate change because there is more carbon dioxide in the atmosphere. Even a politician in Georgia could potentially be affected.”

Veblen came to CU Boulder in 1981 after six years of research in Chile and New Zealand, which taught him the value of creating plots where trees could be viewed long-term.

“I knew from my research experience in the Southern Hemisphere that I wanted to establish permanent forest plots, which are essential to understanding long-term changes in tree populations,” he says. There is no substitute for that.”

With money from a short-term program funded by the State of Colorado, he and his students created 40 “long-term monitoring plots,” identified 8,000 trees in Newt Ridge and have been monitoring them ever since.

“The proposal…was to assess the impact of climate variability on tree demographics and population changes, mortality, and establish new (new tree) seedling recruitment,” says Veblen. The second objective was to study the effects of 19th-century fires on lower elevations of Ponderosa pine and Douglas-fir forests.

One of the key findings of Veblen’s research: While tree mortality rates remained low and stable until 1994, they have tripled since then, even in high elevations of English spruce and pine forests.

“This is not at all surprising… given the warmer temperatures and the greater the aridity,” says Veblen, noting that researchers reached the same conclusions in locations across the western United States.

Meanwhile, new trees don’t fill in the gaps.

Robert Andrews, a former graduate student at CU Boulder and now a postdoctoral researcher at Washington State University, harvested about 1,000 juvenile trees to determine their establishment dates and found that the new trees grew in “pulses of odd years, cooler and wetter years,” based on Late spring and summer weather conditions, Veblen says.

But the incidence of such years has fallen by two-thirds in the last half of the seven decades recorded by Andrus.

Without cold, wet years, we wouldn’t establish new seedlings, including after fires, says Veblen. “This is an indication of what is likely to continue as temperatures rise.”

Even pine trees, which are notorious for colonizing burned areas—the tree’s cones open after exposure to fire—fail to regenerate in places. In areas severely burned in 2002 in the Root and White River National Forests that were sampled repeatedly over a 15-year period, there are only sparse, incomplete seedlings of this fire-adapted species, which usually root within a year. or two.

These trends have convinced Veblen and other researchers and forest managers that western forests need a helping hand from humanity, especially after devastating wildfires.

“If we want to have forests after fires, we need to not rely on natural regeneration. We need to invest heavily in artificial regeneration,” Veblen says, planting seedlings and planting them in strategic areas.

Andros agrees. “We have bark beetle outbreaks and wildfires causing apparent tree death in Colorado. But we are showing that even in areas where people are hiking and where the forest appears healthy, the mortality rate is increasing due to heat and drought alone,” he added:

“It is an early warning sign of climate change.”

Veblen and the broader fire management community agree that “living with fire” is an increasing challenge, as evidenced by modeling projections that say, “Exceptional fire seasons such as 2020 will become more likely, and wildfire activity under future extreme conditions is projected to exceed any Something that hasn’t been seen yet.”

In the Wildland Urban Interface areas, called “red zones” that are so abundant in the West, Veblen has recommendations: Property owners should still create “defensible spaces.” Building codes should be used to require less flammable building materials. Priority should be given to “reducing fuel” by combining logging with specific fires near populated areas to give firefighters a foothold.

However, Veblen says, in remote areas, mechanical mitigation alone is not effective and impractical. Instead, he says, managers are increasingly focusing on the value of allowing wildfires to do the work of reducing fuel and mitigating the potential for future fires.

“Previously, agencies tended to stress too much mechanical mitigation to reduce fuel, but with the kind of extreme weather conditions that encouraged the 2020 Eastern Troublesome Fire, no practical amount of fuel management can fully protect homes and communities,” he says.

Instead, he would like to see resources currently devoted to reducing fuel in remote areas redirected into growing seedlings and transplanting them to suitable, selected areas.

“We will not be able to prevent large and dangerous fires, so we need to be more strategic in investing our resources to avoid or delay some of the worst consequences of climate change,” he says.

Provided by the University of Colorado at Boulder

the quote: Beleaguered Forests Are Declining (2023, March 29) Retrieved March 29, 2023 from https://phys.org/news/2023-03-beleaguered-forests-ground.html

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