Extreme heat represents a new threat to trees and plants in the Pacific Northwest

PORTLAND: From June 25 to July 2, 2021, the Pacific Northwest experienced a record-breaking heat wave that sent the normally temperate region into Death Valley-like extremes that took a heavy toll on trees as well as people.

Seattle and Portland, Ore., recorded their hottest-ever temperatures, reaching 108 degrees Fahrenheit (42.2 Celsius) and 116 Fahrenheit (46.6 Celsius), respectively. In British Columbia, the small town of Lytton reached 121 degrees Fahrenheit (49.6 Celsius).

What become known as the “heat dome” is estimated to have killed hundreds of people in Oregon, Washington and British Columbia.


As this human tragedy unfolded, a lesser-known ecological tragedy was happening, one that scientists warn has grim repercussions for the world’s plants and the many animal species that depend on them.

In a matter of a few days, the 2021 heat dome turned many of the green leaves and needles on the region’s trees to orange, red and brown.

But, as recent research suggests, tree foliage didn’t simply dry out in the heat. Instead, it underwent “widespread scorching.”

“A lot of this reddening and browning of leaves was just that the leaves cooked. It really wasn’t a drought story,” said Chris Still, professor at Oregon State University’s College of Forestry and a leading researcher on the effects of heat on trees.

Still is part of a growing number of scientists investigating what they say is a new, woefully underestimated threat to the world’s plants: climate change-driven extreme heat.