Global tree cover has increased 7% over the last 35 years — but there's a catch

May 13, 2019, 12:36 p.m.
An aerial view of trees in the Smoky Mountain National Forest.
Photo: Sean Pavone/Shutterstock

Despite the prevailing notion that Earth is losing all its trees, a study published in Nature found that the overall percentage of trees on the planet has actually increased over a 35-year period by 7 percent.

Researchers determined this by collecting and analyzed satellite images to monitor the changes in both tall vegetation, like trees, short vegetation and bare ground. Between 1982 and 2016, trees grew to cover more of the Earth than before 1982, some 864,869 square miles (2.24 million square kilometers), or about three times the size of Texas. Their work was published in August 2018.

While is this is good news on one level — more trees! — it's bad news in other ways. While the amount of tree cover may have increased, we have lost a significant amount of tropical tree cover over that same period. The overall growth offsets the loss, but it's still a loss from a key environmental area.

"It's important to understand that the trees we're gaining are not in rainforests" said Matt Hansen, a University of Maryland professor of geographical sciences and a co-author of the study, said in a statement. "While we saw an increase in tree cover in higher altitudes outside of the tropics, tropical deforestation continues and so do the harmful carbon emissions that result from it."

This is where climate change comes in

That tree cover in higher altitudes also indicates changes in Earth's temperatures because of climate change. Warming in areas around the Arctic, like northeastern Siberia, western Alaska and northern Quebec, allowed for wood vegetation to grow where it previously hadn't.

More recent science backs up this concept. In a May 2019 report, researchers studying the Dahurian larch, the northernmost tree species on Earth, found the hardy trees grew more in China's northern forests from 2005 to 2014 than in the preceding 40 years. They suspect warmer soil temperatures are fueling this tree boom, eating into the permafrost layer and allowing tree roots — especially the roots of trees that are hundreds of years old — more room to roam.

Meanwhile, the Maryland researchers, looking at high-resolution satellite images and using probability sampling, estimate that some 60 percent of land change over the 35-year period was connected directly to human activity while the remaining 40 percent was caused by indirect agents, like climate change.

"The results of this study reflect a human-dominated Earth system," Hansen said. "Direct human action on landscapes is found over large areas on every continent, from intensification and extensification of agriculture to increases in forestry and urban land uses, with implications for the maintenance of ecosystem services worldwide."

Editor's note: This story was originally published in August 2018 and has been updated with more recent information.