Oregon is known for its towering volcanic domes covered in evergreen cover that becomes sparse and patchy on the eastern side of the Cascade Mountains before steepening into the high desert.
The people who know trees best say there are many signs of trouble in Oregon.
“We see forms of stress in all of our tree species,” said Christine Buhl, a forest entomologist with the Oregon Department of Forestry. “We just need to change our expectations of what tree species we can expect to plant and where.”
Researchers have been surveying Pacific Northwest forests by air since 1947. Not much has changed during that time, according to Glenn Kohler, an entomologist with the Washington State Department of Natural Resources, which runs the program in the US. alongside the US Forest Service and the Oregon Department. of Forestry.
Every summer, small high-winged planes hover about 1,000 feet above the tree canopy at about 100 mph. Trained observers look outside both sides of the plane, looking for noticeable tree damage.
Dead trees – completely red or orange conifers – are the easiest to spot, but observers can also spot trees without needles in some areas.
Observers assess the intensity of the damage and map its location. Pilots fly in a grid pattern with flight lines approximately 4 miles apart to cover each strip of forest.
“It’s literally like mowing the lawn,” Kohler said of the flight path.
The paper charts of the past have now been replaced by Samsung Galaxy tablets that track aircraft progress and make mapping easier – and probably more accurate.
Observers need a training season, Kohler said. It can be a dizzying task.
“We’re analyzing 16 to 30 acres per second,” DePinte said, noting that smaller planes can provide a more turbulent ride. “You absolutely have to have a stomach of steel.”
This year, the aerial observation program flew over about 69 million acres of forest in Washington state and Oregon in about 246 hours.
“We are just painting the picture. It’s not a hard science. You are not counting individual trees or inspecting individual trees. The goal is to find out what the main trends are and detect outbreaks,” Kohler said.
The extent of the damage in Oregon, which was first reported by environmental journalism nonprofit Columbia Insightwas staggering to researchers and calls for further study.
“We had never seen anything at this level,” DePinte said. “It pulls you back and makes you pause. Your scientific mind begins to wonder why. We don’t always have the answers. »
Trees are susceptible to bark beetles, root diseases and defoliators such as caterpillars. Aerial surveys help researchers capture the ups and downs of these pathogens.
Healthy trees can generally defend themselves against these threats. When beetles enter the bark of a tree, for example, a healthy tree can repel the beetles by excreting pitch, a sticky substance, where they entered the tree, Kohler said.
But disturbances like drought, wildfires and windstorms can stress trees and weaken their defenses. A large number of dead or dying trees could allow bark beetles to lay eggs, feed their larvae and thrive.
Scientists still have only a crude understanding of the factors causing mass deaths in Oregon, but many see drought as the underlying culprit.
“There are several factors at play here. One of the things most of us agree on: the main factor we have here is hot drought,” Buhl said, meaning the state has been hampered by temperatures above normal and also light precipitation.
DePinte said damage was most pronounced in white, Shasta and red fir trees on the east side of the Cascade Range ridge, where the climate is drier.
Nearly half of Oregon is experiencing severe, extreme, or exceptional drought, according to the US Drought Monitor. The drought is worse in eastern Oregon.
Oregon’s average temperatures have risen about 2.2 degrees Fahrenheit since 1895, according to a 2021 state climate assessment turned over to the State Legislative Assembly. Drought severity has increased over the past two decades, in part due to human-induced climate change, the report says. Summers in Oregon are expected to get hotter and drier.
“We have been hearing about climate change for some time. Climate change is happening. We feel it now,” Buhl said. “These summers are getting hot and long. We see evidence on the landscape. We needed to pay more attention decades ago, but we didn’t.
Buhl said forest health impacts destroy about as many trees as wildfires, which are also now more likely and more intense due to climate change.
Heat waves are also a growing threat. On the west side of Oregon, trees were scorched by the June 2021 heat dome, which sent Portland’s temperature up to 116. Scientists said the intense heat wave was “virtually impossible” without climate change.
Last year, aerial assessments documented nearly 230,000 acres of heat burn in Oregon and Washington, DePinte said. Most of the damage occurred on south-facing hillsides that absorb more sunlight due to the sun’s angle in the sky.
“It was the combination of high afternoon temperatures and the setting sun,” said Chris Still, a professor at Oregon State University’s College of Forestry. “We think a lot of these sheets just baked on site.”
Always speculated that the heat dome may have contributed to the death of this year’s fir trees, but more research and evidence is needed to examine any possible connection.
DePinte said the 2021 burn was the largest on record, meaning the Pacific Northwest has now seen two record damage events to its forests in as many years.