Earth & Conservation

Millions of US Trees Are Dying

Across the United States, trees are dying by the millions -- and climate change is to blame.

Millions of trees are dying across the United States, from Alaska and Hawaii to California and Massachusetts; and while a variety of different causes are most immediately to blame, those causes are virtually all exacerbated by one overriding issue: climate change.

In an exhaustive article in The Guardian, Oliver Milman and Alan Yuhas report that more than 50,000 acres of native ohi'a trees (pictured above) on Hawaii's Big Island have fallen victim to what is known as rapid ohi'a death disease -- in which the evergreen trees' leaves turn yellow then brown over the period of just a few weeks -- since 2010.

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Milman and Yuhas write that warming temperatures "have helped spread four types of beetles that bore into ohi'a bark to feed ... (carrying) disease spore on their wings, in their guts and in the sawdust of burrows, spreading it from tree to tree." Elsewhere on the Big Island, the Pu'uhonua o Honaunau National Historical Park was briefly closed in July while scientists attempted to determine what was killing its coconut and palm trees, among other plants.

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It isn't just Hawaii. In South Miami-Dade county in Florida, "what used to be lush, green fields of majestic avocado trees ... are now acres of blighted groves occupied by withered, fungus-filled tree trunks," according to the Miami Herald. The cause: the redbay ambrosia beetle, which is spreading a fungal disease called laurel wilt; the first record of the beetle, a native of Asia, in the U.S. was in 2002 in Georgia, where it likely arrived in solid wood packing material.

In Harvard Forest, in the Great Smoky Mountains National Park and elsewhere in the eastern part of the country, another invasive insect -- the hemlock woolly adelgid -- is taking advantage of warming temperatures to spread among eastern hemlocks, which it kills by eating the trees' vital stored starches. A die-off of aspen in Colorado was due primarily to water stress as a result of drought; while in Washington State, "from mountain forests to city parks, trees that suffered terribly in (a 2015) drought are dying, and burgeoning pests are taking advantage of stressed trees struggling to hang on. Statewide, officials are seeing trees with red needles, dead tops, dying branches, dropped needles and other signs of stress."

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California has been heavily affected. Milman and Yuhas report that in the northern part of the state, an invasive pathogen called Sudden Oak Death is infecting hundreds of plants, "sapping the life" from oaks and other trees and turning them brown. In the Sierra Nevada, a "lethal combination of drought, heat and voracious bark beetles ... killed 26 million trees" between October 2015 and June this year; officials estimate that 66 million trees have died in the state since 2010.

Milman and Yumas note that such widespread tree deaths will likely have cascading impacts, from depriving birds and mammals of their food to undermining the fundamentally essential role that trees play: "providing clean water, locking up carbon and sheltering whole ecosystems."

In California, officials have a more immediate concern. Such a large number of dead and downed trees in effect provides vast amounts of kindling for drought-influenced forest fires: victims of climate change literally fueling one of global warming's most destructive impacts.

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As a recent article in the scientific journal Trends in Ecology & Evolution notes, the world's largest trees are among the longest-living organisms on Earth, and play important roles in ecosystems across the planet. But these majestic giants also face a range of serious threats, from deforestation, drought and invasive species to climate change. With a nod to Arbor Day, here 's a rundown of some of the Earth's biggest tree species -- and what ails them. The Giant Sequoia is found only in about 75 groves along the western slope of the Sierra Nevada mountains in California. The tallest specimen is around 274 feet in height. According to Yale's Environment 360 website, giant sequoias face a threat from climate change, because longer summers and insufficient snowpack from drought may make it difficult for young trees to survive.

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Named after its discoverer, 18th-Century Scottish biologist David Douglas, this species can grow to over 300 feet tall. It's found over a wide area ranging from British Columbia to Mexico. Once-vast forests of the trees have been decimated by logging.

This tree is also known as the English oak, though it's found across a wide area in Europe, northern Africa, and western Asia. It's also been imported to the northeastern and midwestern United States. One specimen in Poland grew to more than 140 feet tall. In Europe, this species and others are threatened by the prospect of increased forest fires and stronger winds, according to a 2008 European Union report.

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The Manna gum is found in cooler parts of Australia, where its leaves provide food for koalas. It can grow to nearly 300 feet in height.

This species is native to the central and northern California coast, and is closely related to trees that thrived during the Jurassic Era. Some specimens have lived for 2,000 years, and the tallest has grown to 367 feet. They're threatened by loss of habitat and possibly by climate change as well.

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This tree is found in the Australian states of Victoria and Tasmania, in areas with high rainfall and fertile soils. The tallest examples can stand nearly 300 feet tall. The're at risk from excessive logging. This image shows a clinometer used to measure the height of trees, in Mt. Field National Park, in Tasmania, Australia.

This tropical tree species is found in the southeastern Philippines. A massive specimen that is still growing near the outskirts of San Francisco in northeastern Mindanao reportedly is 288 feet tall. The species is threatened by logging and slash-and-burn deforestation for farming.

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