The species is among some 100 American trees that are staring at the barrel of extinction, according to a sweeping new assessment published Tuesday in Plants People Planet magazine.
Amid an onslaught of invasive insects, a spate of deadly diseases and the pervasive danger of climate change, as many as 1 in 6 trees native to the Lower 48 states are in danger of being wiped out, the scientists say. The endangered list includes soaring coast redwoods, roomy American chestnuts, elegant black ash, and gnarled whitebark pine.
Yet only eight tree species are federally recognized as endangered or threatened. And 17 risk species are not kept in botanical gardens or scientific collections – including Quercus tardifolia. When they die in the wild, these trees are gone for good.
“It’s easy to feel that gloom and doom because … the scale of the crisis right now is really, really big,” said Murphy Westwood, vice president for science and conservation at the Morton Arboretum in Illinois and a researcher. lead author of the study. “We’re losing species before they’re even described.”
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The new study is the first to list and assess the health of all 881 tree species in the contiguous United States — an achievement in itself, Westwood said, because conservation research rarely focuses on plants.
She pointed to discrepancies in the International Union for the Conservation of Nature’s “Red List,” the leading global inventory of the conservation status of species. The list includes twice as many mammal species as members of the order Lamiales, which include ash, teak and jacaranda trees — though the latter group is nearly five times the size of the former.
“Plant blindness” – the human tendency to overlook the plants that surround us – means fewer resources are being spent on the organisms that oxygenate the Earth, feed its animals and store more carbon than humanity will in 10 years. expel. Until a few years ago, scientists didn’t even know how many tree species existed (the correct number is 58,497).
“It’s this big part of life that’s been totally unstudied or under-studied,” Westwood said.
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Now a coalition of scientists led by Botanic Gardens Conservation International is trying to determine how many of those species are at risk of extinction. Westwood helped lead the American effort.
In the United States, she found that more than two-thirds of species had never been assessed for their extinction risk. Others had gone unexplored for decades, even as new diseases and rising temperatures worldwide put their populations at risk.
After five years of scouring scientific journals, searching scientific databases and interviewing experts, the researchers found that parts of America’s forests have been quietly slipping into obscurity.
In the rosaceae family — a diverse group that includes hawthorns and apple trees — more than a quarter of the species are considered endangered, threatened or critically endangered. Half of all ash species are threatened by the invasive emerald ash borer, a jewel-green insect whose larvae feed on living tissue just beneath the bark of a tree. An emerging disease known as “laurel wilt” attacks all three native members of the genus persea, endangering the small, fragrant evergreen trees.
Invasive insects or pathogens are the leading causes of extinction risk, the scientists found. Although trees have highly developed immune systems – a necessity for any creature that survives for centuries – they are easily overwhelmed by diseases they have never encountered before.
And climate change seems to make these threats even worse, said Stephanie Adams, who oversees plant health care at the Morton Arboretum. Trees stressed by extreme weather are easily picked for marauding insects and fungi. Prolonged drought robs trees of the water they need to produce resin, the sticky substance they use to seal wounds and trap potential invaders.
“There are trees that have been living in locations for hundreds and hundreds of years and suddenly they are now dying,” Adams said.
Not all threats come from abroad. In some cases, changing environmental conditions can turn previously benign organisms into killers.
Adams pointed to an outbreak of fire blight under the oak trees in the Midwest. Although the trees have long lived with the fungus that causes the disease, they only started dying in recent years. Researchers think that escalating severe storms and severe flooding — trademarks of rising global temperatures — promote the growth of the fungus at the expense of its tree hosts.
Bur oaks have not yet fallen into the IUCN’s “vulnerable” category, Adams said. But it’s not hard to imagine that the rapid changes in temperature and weather patterns could suddenly send a once-healthy species into a precipitous decline.
“Oh dear.” Adams took a deep breath. “That’s a terrible thought.”
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The decline of American trees is just one part of a wider crisis plaguing the planet. A 2019 report from the United Nations Panel on Biodiversity and Ecosystem Services estimated that 1 million species are at risk of extinction. The global extinction rate is at least tens of hundreds of times faster than normal and still increasing, threatening to eclipse some of the largest mass die-offs in Earth’s history.
The threats to trees are especially concerning, Westwood said, because of the obvious role they play in nature. Trees are the largest and longest-living organisms on Earth. They frame ecosystems, provide habitat for other creatures, and even create their own weather.
And trees play a vital role in humanity’s efforts to avert catastrophic climate change. The United States’ plan to halve emissions by the end of the decade relies on forests to offset about 12 percent of the pollution that is warming the planet. Disease outbreaks, wildfires, drought, logging and pollution can jeopardize that plan.
“We have a narrow and fast-closing window to take action,” Westwood said, but there’s still plenty the world can do.
Governments can curb the pollution from greenhouse gases – mainly from the burning of fossil fuels – that threatens to warm the planet by 2.5 degrees Celsius (4.5 degrees Fahrenheit) by the end of the century. Communities can adopt stronger policies to protect existing forests and ensure that reforestation projects provide a diverse mix of plant species that are more resilient to emerging threats. Researchers can collect endangered species to ensure they are preserved in botanical gardens, and study those garden specimens to develop strategies to protect their cousins in the wild.
“And then there are things we can all do as individuals,” Westwood said: Plant native species in our gardens. Volunteer in the local forests. Avoid transporting firewood or other material that may contain dangerous vermin.
Human lives depend on the shadow trees cast on the burning city streets, the way their roots and leaves filter the water and air. A healthy forest can slow a wildfire, absorb a storm surge from a hurricane, and comfort a heart in turmoil.
“It’s not altruistic,” Westwood said. “We’re not doing this because we’re tree-hugging nature lovers.”
People need trees just as much as trees depend on us now, Westwood continued. “All of these actions are critical to our very survival as a species and our future on this planet.”
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