Drought, beetles and tree disease still biggest threats to Oregon’s forests, latest aerial survey finds
SALEM, Ore. (KTVZ) – A new report on the state of health of Oregon’s forests shows that drought, insect pests and tree diseases continue to be the biggest threats to the state’s trees.
The report is based on an extensive aerial survey of Oregon’s forests completed last year by the Oregon Department of Forestry and the USDA Forest Service. It's available at https://www.oregon.gov/odf/forestbenefits/documents/forest-health-highlights.pdf
“A large part of this report is devoted to looking at the impact from climate change, specifically drought," said ODF Forest Entomologist Christine Buhl, who helped produce the report.
"Drought is often paired with rising temperatures, and together these are often the underlying causes for tree mortality across our landscape," Buhl said. "Drought reduces tree growth and increases susceptibility to insect pests and some diseases, which healthy trees may otherwise resist or tolerate.”
Buhl said the report also measures other causes of trees being injured or killed, such as insect pests, diseases, storms and wildfires.
Last year, a record 1.9 million acres were affected by wildfire. However, some of those acres contained sections that were not damaged, not all of the burned areas were forested, and not all forests burned with the same intensity, officials said. Some areas that experienced low-intensity wildfires, in many places because of fuel-reduction work, may see a majority of their larger-diameter trees survive.
Areas hardest hit by drought, such as the eastern foothills of the Cascades and some parts of northeastern Oregon, saw the largest amount of non-wildfire tree damage — some 2.26 million acres.
Within those 2.26 million acres is a mosaic of unaffected and current-year affected acres of forest. In 2024, 580,000 affected acres of damage from these agents were recorded. Damage consisted of 496,000 affected acres of tree injury, most of which (463,000 acres) was caused by Swiss needle cast, a foliar disease from which trees may recover. But 84,000 acres showed tree deaths.
“We may be under-reporting the impact of many tree-killing diseases, because the signs can often be missed from the air," Buhl said. "For example, root diseases require ground-based assessment, such as excavating roots, to verify the presence of disease. This is labor-intensive, so is not done routinely across all forestlands.”
Buhl emphasized the importance of on-the-ground collaborators to help round out the full picture of forest health in Oregon.
“In addition to information ODF and the USDA Forest Service gather, we rely on Oregon State University Forestry Extension staff from across the state, and collaborate with other natural resource agencies, universities, public and private forest landowners, and members of the public to gather information,” she said.
In the aerial survey, trained observers fly over all forested lands in the Pacific Northwest in fixed-wing aircraft and record damage to trees from all sources. Flights are staffed with one observer on each side of the aircraft. Survey flights typically fly between 1,500 to 2,500 feet above ground level, following a systematic grid four miles apart and traveling at 90 to 140 miles an hour.
The Pacific Northwest Aerial Detection Survey is the longest continuous survey of its kind in the United States, having been established in 1947 and flown every year since, except 2020, when it was halted due to the COVID-19 pandemic.
