Climate change threatens world's oldest, tallest trees

Approximately one-third of the world's old growth forests were lost between 1900 and 2015.

Laurel Kornfeld | May 31, 2020

Climate change is killing the world's oldest and tallest trees and shortening both the lifespan and height of younger trees, according to a new study published in the journal Science.

Large and old trees are being lost to warmer temperatures, wildfires, development, logging, invasive insects, and deforestation, noted the study's lead author Nate McDowell of the Pacific Northwest National Laboratory in Richland, WA.

Old growth forests absorb and store large amounts of carbon dioxide. They are also home to many rare and endangered species and strongholds of biodiversity. Their loss will therefore accelerate global warming and ecological destruction.

"Perhaps more concerning is that the trajectory of all these disturbances are generally increasing over time and are expected to continue increasing in the future," McDowell said.

A tree physiologist who works with the US Department of Energy's Pacific Northwest National Laboratory, McDowell assembled a team of more than 20 scientists, who reviewed over 160 previous studies on the deaths of trees worldwide.

The team studied records of old growth forests between 1900 and 2015 and found that almost one-third of old growth forest was lost during this 115-year period.

They then combined these studies' findings with satellite data and computer models to produce what is likely the most detailed report of how forests on Earth are changing.

In North America and Europe, where more forest data is available than in other parts of the world, they found that the mortality of trees over the last 40 years has doubled.

The rates of old growth forest decline vary in different parts of the world; however, the researchers warned that the effects of the loss will be felt worldwide.

Disasters over this past year, such as wildfires in Siberia, the Amazon and Australia, decimated the world's old growth forests, as did deforestation and illegal logging in Brazil and Southeast Asia.

In addition to causing or aggravating many of these disasters, climate change is inhibiting forests' ability to recover from catastrophic events.

While increases in atmospheric carbon dioxide can spur tree growth in some locations, that growth is nowhere near enough to compensate for the losses caused by climate change, explained Kristina Anderson-Teixiera, an ecologist who heads the ForestGEO Ecosystems and Climate Program at the Smithsonian Conservation Biology Institute and took part in the study.

"We as a human society are hitting these forests so rapidly with so many different changes that they can't keep up," she said.