timeGiant sequoias are so huge that they were once considered indestructible. High in the Sierra Nevada Mountains of southern California, the oldest trees (known as monarchs) have stood for more than 2,000 years.
Today, however, in Sequoia National Park, giant tree trunks lie on the forest floor like the carcasses of blue whales stranded on the beach. Many trees have been cut down due to drought and fire. But one of the factors contributing to the rising death toll is a new tiny suspect: bark beetles.
In addition to wildfires and rising temperatures, scientists worry the insects could contribute to the collapse of the planet’s northern taiga, a forest that stretches across Canada, Scandinavia, Siberia and Alaska vast ecosystem.
Boreal forests cover 11.3 million square kilometers (2.8 billion acres) and store approximately 272 gigatons of carbon. Its possible collapse is considered a climate tipping point: the moment an ecosystem that previously served as a store of carbon switches to releasing large amounts of carbon through forest fires or gases released from rotting trees and eroding soil.
“This is a global phenomenon, but it’s also a complex story,” said Professor Diana Six, a forest entomologist at the University of Montana. “There are different beetles in different forests and they behave differently.
“The only common denominator, and the reason we see so many events at the same time, is human impact. Climate change is the main reason, but we have also changed the forests significantly.
Scientists are careful not to bring a stigma to the beetle. They are highly specialized – most of them have no impact on their tree hosts – but researchers are convinced their impact is growing.
In Canada, the mountain pine beetle alone affected an area of 200,000 square kilometers (almost the size of Uganda) between 2000 and 2020, with other species causing outbreaks elsewhere across the country.
Disturbance of forests by bark beetles has increased dramatically in Europe, particularly affecting monocultures of Norway spruce. In the Czech Republic, the epicenter of the continent’s latest outbreak, up to 5.4% of spruce trees were destroyed each year between 2017 and 2019, converting its land from a carbon sink to a carbon source, with catastrophic consequences for the region .
According to the U.S. Forest Service, bark beetles killed 163 million trees in California between 2010 and 2019. Outbreaks have been documented across large swathes of Siberian taiga, but their impact is largely unknown.
“In these cases, the beetles are far beyond normal,” Six said. “Couple that with climate change changing the ability of these trees to regenerate, and I think that’s the biggest problem we’re going to see.”
“If beetles kill a bunch of trees and then they grow back, it’s not a big deal,” she said. Wildlife on the verge of disappearing: A mass extinction.
The infestation was first discovered in giant sequoias in 2017. Park officials believe at least 21 large trees in the park infected by the western cedar bark beetle are unlikely to survive: they die from top to bottom, a pattern consistent with bark beetle damage.
More trees are at risk throughout the park, including the world’s largest General Sherman tree. They are part of a growing trend in the northern hemisphere’s taiga, which has led to the loss of tens of millions of trees.
SecondArk beetles are a highly diverse group of insects and a natural part of ecosystems, with hundreds of species found worldwide. But parts of this insect family have now cleared vast tracts of forests in Canada, Siberia, Scandinavia, the United States, Mongolia, China and Japan.
High in the canopy of the King Sequoia, a mirror hangs: part of an installation designed to observe the presence of beetles in the canopy. Nathaniel Foote, the Colorado researcher who led the work, explained that it’s part of an international effort to understand how fire, drought and insects interact to damage trees.
While the exact pattern of bark beetles killing trees is unique to each species, many bark beetles follow a similar pattern: conifers are overrun by the beetles, which lay eggs under the bark, and the resulting larvae chew through the trunk, Slowly stop the spread of nutrients through the plant. Their green spines turn a sickly orange and then die. The orange scars in the forest eventually turned gray.
In some areas this is a natural process, but the unpredictability of temperatures due to global warming has made bark beetle behavior even more unpredictable, sometimes exacerbated by high temperatures, weakened trees and large monoculture plantations.
Trees have natural defenses against insects, producing resins and other reactions to fight off insect attacks. But these defenses are not enough to prevent them from being overwhelmed amid growing pressure from drought and global warming. As trees struggle to get enough water, they can’t produce enough sap to fight back.
At what point, Foote asked, would beetles become involved in the death of a giant sequoia. “We’re not quite sure. But in a really extreme drought scenario, people would certainly be concerned. I think we’ve entered a series of unprecedented events.
The consequences of bark beetle outbreaks are complex. Although there will be fewer trees in the medium term, the consequences can sometimes boost biodiversity in the long term. Destroyed man-made forests and plantations can regenerate naturally, providing space for endangered species that have been squeezed out.
But in some areas, such as parts of the Rockies, scientists suspect that bark beetle outbreaks and other factors will permanently convert forests to prairie as the region becomes too warm for tree cover to recover.
The epidemic is spreading northward into parts of the world that were previously too cold for the insects. Normally, their larvae are killed by freezing conditions, but in some places rising temperatures mean this no longer happens.
Thomas Seth Davis, a bark beetle researcher at Colorado State University, said: “The combined pressures of climate change and bark beetles may lead to changes in carbon sequestration, accelerating the rate of climate change.
“You could have this feedback effect where if we lose the carbon sequestration potential of these boreal forests, warming becomes faster.”
This year, France is the latest country to struggle to control an outbreak of the beetle in the wake of drought and high temperatures. Scientists fear this may be just the beginning.
Thomasáš Hlásny, a professor at the Czech University of Life Sciences who has led research into the impact of bark beetles in Europe, said the biggest issue is stopping carbon emissions, not stopping the spread of the insects.
“These epidemics and wildfires are manifestations of climate change. People still believe that if they take steps, we can carry on as usual. That’s wrong,” he said.
“We’re basically losing the fight against climate change, not the bark beetle.”
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