Forests Struggle on New Planet

March 15, 2021

A boardwalk in the Mariposa Grove in Yosemite damaged by a fallen ponderosa pine during the Mono wind event on 19 January.
A boardwalk in the Mariposa Grove in Yosemite damaged by a fallen ponderosa pine during the Mono wind event on 19 January.Photograph: AP

In geological time, we’ve changed the climate in the blink of an eye – pulling the biological rug out from under forests around the planet.

Guardian:

Camille Stevens-Rumann never used to worry about seeing dead trees. As a wildland firefighter in the American west, she encountered untold numbers killed in blazes she helped to extinguish. She knew fires are integral to forests in this part of the world; they prune out smaller trees, giving room to the rest and even help the seeds of some species to germinate.

“We have largely operated under the assumption that forests are going to come back after fires,” Stevens-Rumann said.

But starting in about 2013, she noticed something unsettling. In certain places, the trees were not returning. For an analysis she led of sites across the Rocky Mountains, she found that almost one-third of places that had burned since 2000 had no trees regrowing whatsoever. Instead of tree seedlings, there were shrubs and flowers.

This shift – echoed across a warming world – is a distinct phenomenon from trees dying because of direct human intervention such as logging. These trees are dying without humans laying a hand on them, at least physically, and they are not resprouting. Forests cover 30% of the planet’s land surface, and yet, as humans heat the atmosphere, some locations where they would have grown now appear too dry or hot to support them.

In western North America, huge swaths of forested areas may become unsuitable for trees owing to climate change, say researchers. In the Rocky Mountains, estimates hold that by 2050, about 15% of the forests would not grow back if felled by fire because the climate would no longer suit them. In Alberta, Canada, about half of existing forests could vanish by 2100. In the south-western US, which is experiencing a “megadrought”, as much as 30% of forests are at risk of converting to shrubland or another kind of ecosystem.

“Now’s a good time to go visit national parks with big trees,” said Nate McDowell, an earth scientist at the Pacific Northwest National Laboratory and the lead author of a paper forecasting that in southwestern US forests more than half of conifers, the dominant type of trees, could be killed by 2050. “It’s like Glacier national park – now’s a good time to see a glacier before they’re gone.”

The change isn’t unique to the US and Canada. In the Amazon, some experts warn that a forest mortality tipping point is looming. The boreal forests of Siberia are under attack from higher temperatures. Temperate European forests thought to be less vulnerable to climate change are showing worrying symptoms.

Forest mortality researchers say while this does not mark the end of the forests, it may well be the end of many forests as we’ve known them.Iconic species such as giant sequoias and Joshua trees are succumbing in remarkable numbers. The landscapes of beloved wild places and national parks are, in turn, being transformed. And the changes being observed today – in which slow-growing trees that have survived for hundreds of years are dying in a drought or wildfire – cannot be undone in our lifetimes.

he possibility of worldwide mass forest mortality linked to climate change was flagged in the first Intergovernmental Panel on Climate Change assessments in 1990. But today, many researchers are expressing particular concern about the tree mortality crisis building in California and other parts of the west.

Since 2010, 129m trees are estimated to have died in California’s national forests, as a result of a hotter climate, insects and other factors. Astonishingly, 48.9% of all trees in a comprehensive study of the southern Sierra Nevada mountain range were killed.

The effects of a warming planet on trees were already obvious in summer 2016, as California was emerging from its driest four-year period since scientific record-keeping began. In August that year, I drove from San Francisco to the foothills of the Sierra Nevada to visit Steven Ostoja, the director of the US agriculture department’s California Climate Hub. At his house on the rural outskirts of a community called Oakhurst, Ostoja led me into his yard.

“I watched that tree die,” he said, gesturing toward a 40ft-tall ponderosa pine. We crunched across yellowed grass and leaves to examine it. The ponderosa was wizened and bleached by the elements. Up close, Ostoja was able to pull off a chunk of bark as easily as peeling a tangerine. He pointed out dozens of small holes along the bark made by burrowing beetles. Small, hard blobs of pitch, resembling honey, indicated where the tree had tried to push them out, but lacking water, it had not been able to produce enough.

Dehydration is not always the culprit when trees die in droughts. Droughts often create such hostile conditions that trees with decades or centuries of life ahead of them are suddenly vulnerable to insects or disease, or to wildfires that can rampage when the environment dries out.

The distant whine of a chainsaw taking down a dead tree served as a reminder of the extent of the problem. “That’s a sound you hear all the time,” Ostoja said. “You’ll hear it on a Monday, on a Tuesday, all day long.”

Ostoja had an unruffled scientific manner, but even so he was perturbed by the speed of the change he had witnessed. “It wasn’t within a career,” he said. “It was within three years.” He wondered aloud whether this was one of the most pronounced ecological shifts in the western US “in such a short period of time in the last 10,000 years”.

Researchers acknowledge that there is considerable ambiguity in their predictions about tree mortality. For one thing, it is unclear how many of the trees now dying essentially weren’t meant to be there in the first place. Western forests are denser than they were historically because of human influence: the practice of tamping out wildfires, beginning in the early 20th century, has interfered with a natural process in which blazes weed out younger trees and undergrowth.

Even so, the tree mortality problem spanning the western part of the continent is prompting a broad and looming sense of disquiet. Take New Mexico, which has just experienced one of its driest two-decade periods in 1,200 years. At Bandelier national monument, recent wildfires have left bare landscapes. “Why aren’t we getting pine regeneration?” the monument’s chief resource manager said to the Durango Herald in 2017. “We may have to redefine recovery, because we’re not sure some of these forest types will ever return.”

Not far away, ecologist Craig Allen just marked his 40th year studying forests and landscapes in the Jemez mountains. When he arrived from the cooler climes of north-east Wisconsin, moist weather patterns made the region “a great place to be a tree in the south-west US”. That natural variability has now, thanks to climate change, flipped to megadrought conditions. By mid-century, Allen suspects, trees will barely cling to existence in the mountains of the south-west.

“I have to be a little careful about not sounding like some Cassandra saying the sky is falling and forests are going to die and burn – but I have seen what that looks like,” said Allen, who founded the US Geological Survey’s New Mexico Landscapes Field Station.Advertisement

On a personal level, he added, “it’s actually disorienting to me to be out in the landscapes in some ways because they’re so different from how I first knew them. Now you see a vista literally for 100 miles – you see the next mountain range 100 miles away. And [previously] you couldn’t see more than 20 meters. The canopies are thin, the whole productivity and vigor of the system is suppressed.”

A series of photographs taken in 2011, 2013 and 2014 by researcher Craig Allen in the footprint of the Las Conchas fire, a 2011 ‘megafire’ in the eastern Jemez mountains. The images show little tree regrowth.

A series of photographs taken in 2011, 2013 and 2014 by researcher Craig Allen in the footprint of the Las Conchas fire, a 2011 ‘megafire’ in the eastern Jemez mountains. The images show little tree regrowth. Composite: Craig Allen

5 Responses to “Forests Struggle on New Planet”

  1. pendantry Says:

    “I have to be a little careful about not sounding like some Cassandra saying the sky is falling and forests are going to die and burn – but I have seen what that looks like,” said Allen

    Interesting point of view; he’s more concerned about how his message is perceived than the truth of the message itself. Isn’t that the very attitude that has brought us to this point?

    I’m reminded of a conversation with a statistician on Greg Craven’s ‘Manpollo Project’ forum (which has long since bitten the dust). When discussing the idea of initiatives to promote massive tree-planting programmes, this statistician (his name escapes me) insisted that before considering any such venture, it would be necessary to first conduct a full environmental impact assessment. /eyeroll

  2. Frank Price Says:

    “One of the penalties of an ecological education is that one lives alone in a world of wounds. Much of the damage inflicted on land is quite invisible to laymen. An ecologist must either harden his shell and make believe that the consequences of science are none of his business, or he must be the doctor who sees the marks of death in a community that believes itself well and does not want to be told otherwise.” — Aldo Leopold

  3. doldrom Says:

    I would be curious to know if there is also a trend in how hot these fires are burning compared to the natural fires of ages past, and what the effect of this could be for regeneration.

  4. rhymeswithgoalie Says:

    For an analysis she led of sites across the Rocky Mountains, she found that almost one-third of places that had burned since 2000 had no trees regrowing whatsoever. Instead of tree seedlings, there were shrubs and flowers.

    I don’t know if it applies in these areas, but in some places tree saplings are vulnerable to an excess* of deer. I’m an advocate of not only releasing wolves into the wild, but releasing them into the upscale developments where the residents whine about the deer eating everything. 😉

    ________
    *Don’t let deer hunters who only go after bucks tell you about the importance of hunting for culling. You cull by reducing the number of reproducing does available; surviving bucks can cover a lot of does.


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