By Glenn Kohler, Forest Entomologist, Washington State Department of Natural Resources, firstname.lastname@example.org
Each spring, the Washington State Department of Natural Resources and U.S. Forest Service publish a Forest Health Highlights report that summarizes forest health conditions and trends across Washington from the previous year. The 2018 report and previous year’s reports are available on DNR’s Forest Health website.
Information for the report is gathered through annual monitoring projects and special surveys in response to recent forest damage events that are conducted by DNR and the Forest Service. Examples include an annual aerial survey, insect trapping, baiting streams for the pathogen that causes sudden oak death and installing ground plots to monitor emerging forest health issues, such as bigleaf maple decline.
The report also summarizes recent wildfire activity, weather events and drought conditions that may affect forest health, and forest health initiatives such as the Forest Health 20-Year Strategic Plan for Eastern Washington. Maps, charts, photos, and brief descriptions make much of the information in the report accessible at a glance.
For those who want more detail, it includes links to other resources like maps and data and the contact information of forest health specialists.
Annual Insect and Disease Aerial Survey
An annual insect and disease aerial survey that covers the majority of Washington’s 22.4 million acres of forested lands provides much of the trend information in the report.
Every year since 1947, aerial observers have reported the location and intensity of damage by forest insects, diseases, and other disturbances across all ownerships of forestland in Washington.
Without aerial surveys, it would be impossible to track disturbance conditions over such a large area using ground-based methods. Aerial survey is also an important tool used to detect and map new outbreaks of native and exotic insects and diseases.
The total area mapped with some type of damage varies each year from a few hundred thousand to nearly 2 million acres.
Last year was the first time aerial observers in Washington adopted new federal data collection standards and used new software on digital mobile sketch mapping tablets.
When observers record a small area with tree mortality (fewer than 2 acres), they assign an estimate of number of trees affected. For larger areas with tree mortality, observers no longer estimate trees per acre as a measure of damage intensity. Instead, they now choose a “percent-class” value that estimates the percent of treed area affected.
2018 Aerial Survey Highlights
Smoky conditions and temporary flight restrictions around active wildfires in 2018 prevented observers from conducting any flights from early August to early September.
Fortunately, due to earlier-than-normal onset of damage signatures, observers were able to cover most of the survey area prior to poor visibility setting in across Eastern Washington. Improved visibility, favorable weather, and fewer flight restrictions allowed observers to complete the survey by the end of September.
In 2018, the aerial survey recorded some level of tree mortality, tree defoliation, or foliar diseases on 469,000 acres, similar to the 512,000 acres with damage in 2017.
The area with mortality from bark beetles was 235,000 acres. Mortality due to bear damage or root disease was mapped on 115,000 acres. Relative to 2017, tree mortality decreased for all major bark beetle species except fir engraver.
The area with conifer defoliation was 28,200 acres, primarily caused by balsam woolly adelgid and western spruce budworm. Approximately 16,300 acres had some level of disease damage, primarily larch needle cast and bigleaf maple decline.
It should be noted that disease damage is significantly underrepresented in aerial survey because symptoms are often undetectable from the air.
At 120,000 acres with damage, pine bark beetles made up the majority of bark beetle activity, but well below a recent peak of over 400,000 acres in 2009. The most significant damage occurred in northern Ferry County, eastern Okanogan County, and Chelan County.
Fir engraver caused mortality in true firs (Abies species) was recorded on 71,200 acres in 2018, the highest level since 2009. Recent drought conditions and effects of past defoliation by western spruce budworm are likely drivers of the increase.
An outbreak of Douglas-fir tussock moth has caused severe defoliation on approximately 1,900 acres in Kittitas and Chelan counties. This is the first observation of tussuck moth defoliation in Washington since 2012 and the first in Kittitas County since aerial surveys began in 1947.
Western spruce budworm defoliation, primarily in northeast Washington counties, decreased significantly to approximately 7,500 acres, the lowest level observed in the state since 1970.
A new outbreak of western hemlock looper has caused light to moderate intensity defoliation on approximately 870 acres in south Whatcom and north Skagit counties. This area experienced a similar sized outbreak in 2011-2012.
Larch needle cast damage in western larch was observed on approximately 4,900 acres, primarily in the central and south Cascade Mountains.
Crown discoloration and dieback in bigleaf maple was observed on approximately 6,100 acres, primarily in lowlands of southwest Washington and in the south Puget Sound area.
Maps and Other Aerial Survey Products available to the public:
Whether you are a regular user of aerial survey maps and data or just learning about what’s out there, check out some of the products now available.
- Downloadable PDF aerial survey quad maps from 2003 to the most recent year are available from the U.S. Forest Service, Pacific Northwest Region
- Interactive, web-based aerial survey maps are available to explore: Look in the Forest Health folder on DNR’s mapping site.
- Draft data can be reviewed by users during the survey season using the ADS Data Review Map
- Washington’s annual Forest Health Highlights report is available online (also viewable at on the U.S. Forest Service, Pacific Northwest Region website)
If you have any questions about these products or need information about forest insects and diseases, please contact the DNR Forest Health Program at 360-902-1300 or email email@example.com.