Throughout the U.S., trees are dying at an astonishing rate. The reasons for the die-off vary from location to location -- drought, disease, insects and wildfires -- but the root cause in many of these cases is the same: climate change.
The epidemic is even threatening the oldest white oak tree in America, a 600-year-old giant in New Jersey that predates Columbus' visit to the Americas.
The effect is particularly apparent in mountain states like California, where 66 million trees have simply disappeared from the Sierra Nevada range since 2010. The Forest Service blames the years-long drought in the area and the spread of pine beetles.
In northern California, the ominously named "Sudden Oak Death" is infecting hundreds of different plants, from massive redwoods to backyard oaks. The disease is transmitted through water, so it can easily be spread by wind and rain over long distances. In fact, the spread already spans more than half the length of the state.
The presence of so many dead trees would be a tragedy anywhere, but in the mountains of the West, it's particularly dangerous because the trees provide fuel for forest fires. It's impossible for forest workers to chop down and remove millions of trees, so the majority of them are still standing.
In some cases, death and disease have overtaken entire mountainsides. Some researchers estimate that we could lose all needle leaf evergreens in the Southwest U.S. within the next hundred years.
In Hawaii, the islands are losing their once-abundant ohi'a trees at an alarming rate. Over the past six years, the big island has lost nearly 50,000 acres to a previously unknown disease that causes rapid death over the course of just a few short weeks. Because it's unlike anything scientists have ever seen before, researchers are unsure how to treat it. While the plague is affecting only a limited area now, locals worry it will spread and collapse the entire native ecosystem.
The disease is caused by a fungus, which grows through the vascular system of the trees, preventing them from drawing water from the ground. Though researchers have examined other plant fungi in an attempt to trace the disease's origins, it appears to be an entirely new strain. There is still no cure for the fungus, so right now the priority is containing the spread of the disease rather than treating it.
In Seattle, tree deaths are even hitting city parks. Pine beetles, once confined to a small part of the country, have spread throughout the U.S., apparently beyond our forests. More than 500 trees have been lost this summer alone -- a normal year would see only about 130 trees culled.
While there's some controversy over whether pine beetles are destroying forests or simply culling unhealthy trees, the fact remains that these tree deaths are a major warning sign.
And it isn't just the Western U.S. that's been affected by the epidemic. In recent years, reports of dying forests have come in from every part of the country. Throughout New England, fro instance, hemlock trees have been slowly dying from invasive insect infestations, forever altering the composition of local forests. Again, climate change seems to be enabling the spread of the pests in a way ecologists have never seen before.
Forests are one of the Earth's most important protections again climate change. The trees themselves act as carbon sinks, sequestering nearly a quarter of carbon dioxide emissions from the air. When they die, that carbon is released back into the air.
In an interview last year with Rolling Stone, Richard Birdsey of the U.S. Forest Service explained, "if the carbon sink in forests fails, a simple speculation is that global temperatures would increase proportionally to the increase of CO2 concentration, so about 25 percent above current climate projections."