70 years of tracking bugs and crud from the air

Forest insects are causing significant damage, and current forest conditions are vulnerable to spread even more. Photo by: DNR

Every year since 1947, forest health surveyors have reported the location and intensity of damage to our forests by insects, diseases and other disturbances across all ownership of forestland in Washington. The survey is completed by plane, of course, which is called an aerial survey.

Without these aerial surveys, it would be impossible to track disturbance conditions over such a large area using strictly ground-based methods. Aerial survey is also an important tool used to detect and map new outbreaks of native and exotic insects and diseases.

DNR and the U.S. Forest Service work together to conduct an aerial survey each year. They cover the majority of forest lands in Washington, which is 22.4 million acres. The total area mapped that has some type of damage varies each year from a few hundred thousand to nearly two million acres.

Using data from the aerial survey, Washington’s annual Forest Health Highlights report summarizes the major insect and disease activity across the state. August is the best time to fly aerial survey in eastern Washington because damage signatures are well developed. But, heavy smoke and temporary flight restrictions due to 2015 wildfires prevented the survey from happening until late September. See what information was gathered for our Forest Health Highlights of 2015.

Aerial Surveys Then and Now 
The methods of the survey affectionately known as the “bugs and crud” survey have come a long way since the early days of open cockpits and paper maps used to navigate the flight and pencil in damaged areas. Today, aerial observers use digital ‘sketchmappers’ that have a moving map display, GPS and a touch screen to help pinpoint the aircraft’s location and map damage more accurately. In the days of paper maps, it took weeks to transfer data by hand to generate map products. Today, observers are able to share digital draft data and draft maps with land managers a few days after the flights are complete; allowing more time for ground verification.

In the Pacific Northwest, the aerial survey is flown on a grid pattern with a pilot and two observers looking over a two-mile swath on either side of the plane while it travels at 90 miles per hour or more. Observers outline areas of damaged trees, input the likely cause of damage and estimate its intensity. Observers are trained to look for ‘signatures’ of specific damage, such as tree species, color of tree crowns and patterns on the landscape. Only current-year damage is recorded. Observers assign each damage area (polygon) one or more unique codes for each agent (insect, disease or weather) involved which are followed by a modifier indicating number of trees affected, number of trees per acre affected, or intensity of damage (light, moderate or heavy). All codes and modifiers are defined in the map legend. When interpreting data and maps, be careful not to assume the mortality agent polygons indicate every tree is dead within the area. Checking the agent code modifier may help you to see if only a small proportion of trees in the polygon may have been recently killed, for example.

Washington insect and disease aerial survey flight lines for 2015. Map by Aleksandar Dozic, DNR
Washington insect and disease aerial survey flight lines for 2015. Map by Aleksandar Dozic, DNR

When things get busy or signatures are not clear, observers can ask the pilot to circle back for a better look. Observers do take photos of damage when there are opportunities, but photos are primarily used for reporting and training, not for analysis. It can be challenging to accurately identify and record damage over such a large scale. Sometimes the wrong pest is identified, the location is off target or damage is missed. The goal is to correctly identify and accurately map within one-quarter mile of the actual location at least 70 percent of the time. Land managers often use this data to point them toward areas in need of on-the-ground assessment when they need more precise information.

For such a large area, the aerial survey remains the most efficient and cost-effective method to track pest and damage trends over time. The annually produced maps and data are indispensable tools used by federal, state, tribal and private land managers to focus forest health improvement efforts on higher risk areas. And these products are freely available to the public.

See this 3-minute video that shows exactly how DNR and the USFS conduct the aerial surveys using a digital aerial sketchmapper.

DNR and the USFS will have the Forest Health Highlights report for 2016 in February 2017.

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 forest_health@dnr.wa.gov.

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