麻豆影院

CU 麻豆影院 scientist鈥檚 40-year census research finds that climate change has tripled tree mortality and forestalled regeneration

Criticizing the Biden administration鈥檚 $3.5 trillion Inflation Reduction Act, a U.S. Senate candidate in Georgia singled out funding to plant and protect trees.

鈥淭hey continue to try to fool you that they are helping you out. But they鈥檙e not. Because a lot of money, it鈥檚 going to trees,鈥� GOP candidate Herschel Walker听said听while stumping at a fundraiser. 鈥淲e got enough trees鈥攄on鈥檛 we have enough trees around here?鈥�

A 2015听study听in听Nature听estimated there are 3 trillion trees on the planet. Whether or not that鈥檚 鈥渆nough,鈥� the survey also found that 鈥渢he global number of trees has fallen by approximately 46% since the start of human civilization.鈥�

And according to a 麻豆影院 scientist who has been monitoring the health and number of trees in the Colorado high country for more than four decades, climate-driven changes in temperature and drought have not only tripled tree mortality rates in the past two decades, but also significantly undermined tree regeneration rates.听

And that matters.

鈥淚f we are losing forest cover, we are going to lose a variety of ecosystem services,鈥� says Tom Veblen, Distinguished Professor emeritus of geography, who has been tracking changes in thousands of trees on Niwot Ridge west of 麻豆影院 since 1982.听

Declining tree cover results in damage to watersheds as debris flow and flooding increase, and in the loss of habitat for certain species. Perhaps most destructive, the loss of 鈥渁bove-ground biomass鈥� removes a vital source of carbon storage, which further fuels climate change.听

鈥淚n most simulation models of ecosystem impacts of climate change . . . the trees grow back after fire. But we鈥檙e not seeing that as documented for montane forests in Colorado,鈥� Veblen says. That results in 鈥渙ne of those nasty, somewhat unexpected positive-feedback loops that speeds up climate change because there is more carbon dioxide in the atmosphere. Even a politician in Georgia will potentially be affected by that.鈥�

Veblen came to CU 麻豆影院 in 1981 after six years of research in Chile and New Zealand, which taught him the value of establishing plots where trees could be observed long-term.听

鈥淚 knew from my research experience in the Southern Hemisphere that I wanted to put in permanent forest plots, which are essential for understanding long-term changes in tree populations,鈥� he says. 鈥淭here is no substitute for that.鈥�

With money from a short-lived program funded by the state of Colorado, he and his students established 40 鈥渓ong-term monitoring plots,鈥� marked 8,000 trees on Niwot Ridge and have been monitoring them ever since.听

鈥淭he proposal . . . was to assess the influence of climate variability on tree demography and population changes, mortality, and the establishment of new seedling recruitment (new trees),鈥� Veblen says. A second goal was to study the effects of 19th-century fires on lower elevation ponderosa pine and Douglas fir forests.

One of the key findings from Veblen鈥檚 research: While tree mortality rates remained low and stable until 1994, they have tripled since then, even in higher elevation Englemann spruce and lodgepole pine forests.听

鈥淭hat鈥檚 not at all surprising . . . given increasing temperatures and increasing drought,鈥� Veblen says, noting that researchers have reached the same conclusions at locations across the western United States.

Meanwhile, new trees are not filling in the gaps.

Former CU 麻豆影院 graduate student听Robert Andrus, now a postdoctoral researcher at Washington State University, harvested about 1,000 juvenile trees to determine their establishment dates and found that new trees grew in 鈥減ulses of single years, cooler, moister years, based on late spring and summer weather conditions,鈥� Veblen says.听

But the occurrence of such years has plummeted by two-thirds in the latter half of the seven-decade record Andrus examined.听

鈥淲ithout cool, moist years, we鈥檙e not getting establishment鈥� of new seedlings, including after fires, Veblen says. 鈥淭hat鈥檚 an indicator of what is likely to continue with warming temperatures.鈥�

Even lodgepole pines, famous for colonizing burned areas鈥攖he tree鈥檚 cones open after exposure to fire鈥攁re failing to regenerate in some places. In areas torched by severe fires in 2002 in the Routt and White River national forests that have been repeatedly sampled over a 15-year period, there are only sparse and patchy seedlings of this fire-adapted species, which usually take root within a year or two.听

Those trends have convinced Veblen and other researchers and forest managers that Western forests need a helping hand from humanity, particularly after destructive wildfires.听

鈥淚f we want to have forests after fires, we need to not rely on natural regeneration. We need to invest heavily in artificial regeneration,鈥� the cultivation and planting of seedlings in strategic areas, Veblen says.

Andrus agrees. 鈥淲e have bark beetle outbreaks and wildfires that cause very obvious mortality of trees in Colorado. But we鈥檙e showing that even in the areas that people go hiking in and where the forest looks healthy, mortality is increasing due to heat and dry conditions alone,鈥� adding:

鈥淚t鈥檚 an early warning sign of climate change.鈥�

Veblen and the fire management community broadly agree that 鈥渓iving with fire鈥� is increasingly challenging, as shown by modeling projections that say, 鈥淓xceptional fire seasons like 2020 will become more likely, and wildfire activity under future extremes is predicted to exceed anything yet witnessed.鈥澨�听

In Wildland Urban Interface areas, so-called 鈥渞ed zones鈥� that are abundant throughout the West, Veblen has recommendations: Property owners must still establish 鈥渄efensible spaces.鈥� Building codes should be used to require less-flammable building materials. 鈥淔uels reduction鈥� through a combination of tree cutting and prescribed fires should be prioritized near settled areas to give firefighters a foothold.听

However, Veblen says, in more remote areas, mechanical thinning alone is not effective and not practical. Instead, he says, managers are increasingly emphasizing the value of letting wildfires do the work of reducing fuels and buffering against future fire potential.听听

鈥淎gencies previously tended to strongly emphasize mechanical thinning to reduce fuels, but under the kind of extreme weather conditions that promoted the 2020 East Troublesome fire, no practical amount of fuel management can fully protect homes and communities,鈥� he says.

Instead, he鈥檇 like to see resources currently dedicated to remote-area fuels reduction be redirected into seedling cultivation and planting in selected, suitable areas.

鈥淲e are not going to be able to prevent large, severe fires, so we need to be much more strategic in investing our resources to avoid or delay some of the worst outcomes of climate change,鈥� he says.听

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