by Glenn Kohler, Entomologist and Aerial Observer, Washington DNR
Every year since 1947, aerial surveyors 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 Washington Department of Natural Resources and the USDA Forest Service cooperate to conduct the annual aerial detection survey (ADS) and typically cover the majority of Washington’s 22.4 million acres of forested lands. The total area mapped with some type of damage varies each year from a few hundred thousand to nearly two million acres.
2015 Aerial Survey Highlights
A very active wildfire season in 2015 posed major challenges for the aerial survey, but crews were still able to complete the survey in all areas unaffected by fire. Approximately one million acres that would have normally been surveyed were not flown in 2015 due to numerous large fires of 2014 and 2015. Because it is difficult to distinguish mortality caused by fire from mortality caused by insects or disease, areas burned by wildfire are not mapped until the second year following the fire. Normally August is the best time to fly aerial survey in eastern Washington because damage signatures are well developed. But heavy smoke, temporary flight restriction areas, and crew and aircraft commitments to fire duty prevented any survey flights the entire month of August. An additional aircraft and crew were used to complete the survey by late September.
In 2015, some level of tree mortality, tree defoliation, or foliar diseases was recorded on approximately 338,000 acres. This is well below the 543,000 acres reported in 2014. Some part of this decrease is due to reduced acres flown in areas of eastern Washington that typically have higher levels of damage. However, downward trends in insect and disease damage were also evident in areas unaffected by wildfires.
Tree mortality was recorded on approximately 241,000 acres, of this 116,000 acres were attributed to bark beetles and 108,000 acres to bear damage or root disease. Relative to 2014, tree mortality decreased for all major bark beetles including mountain pine beetle (58,700 acres), western pine beetle (5,900 acres), Douglas-fir beetle (18,500 acres), fir engraver (11,700 acres), and spruce beetle (16,000 acres). Mountain pine beetle was at the lowest level in the last ten years. The area with conifer defoliation decreased to approximately 99,000 acres, down from 159,000 acres reported in 2014. Almost all defoliation recorded was caused by western spruce budworm (79,000 acres) and balsam woolly adelgid (19,600 acres). Western spruce budworm defoliation was at the lowest level in the last ten years, but similar to 2014. Approximately 9,800 acres had some level of disease damage, primarily bigleaf maple decline (2,700 acres) and needle casts in pines (3,200 acres) and western larch (2,900 acres).
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 completed; allowing more time for ground verification.
In the Pacific Northwest, the ADS 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 is moving along 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 agents, 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 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 legends of map products. When interpreting data and maps, be careful not to assume the mortality agent polygons indicate every tree is dead within the area. Depending on the agent code modifier, only a small proportion of trees in the polygon may actually be recently killed.
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% of the time.
For such a large area, the aerial survey is 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. Washington’s annual Forest Health Highlights report summarizes the major insect and disease activity across the state. For information on how to access these reports, maps, and other aerial survey products, please see the list at the end of this article.
Aerial Survey in the Future
The Forest Service is advocating a national standardization of aerial survey data and its collection methods. The Pacific Northwest Region aerial survey program is testing new tablet-based sketchmappers that are less expensive, lightweight, produce less heat, and can take photos linked to the data by GPS location. Data collected on these tablets will automatically be uploaded to a central server as soon as it’s collected. The lower cost of the new tablets will mean more units can be available for ground-verification work. This new technology may also mean a transition to a new national standard of recording mortality as a percentage of the stand rather than the current trees-per-acre method. Aerial surveyors are evaluating how a change to percent mortality might impact long-term analysis and ways the data is reported.
Aerial observers are often asked why we don’t use unmanned aerial vehicles (UAVs) or drones to accomplish the survey. The answer, for now at least, is that the limitations of the technology, sensors, and regulations can’t compete with the well-trained observers and pilots we use today for a cost-effective and efficient aerial survey.
Maps and Other Aerial Survey Products
Whether you are a regular user of aerial survey maps and data or just learning about what’s available, please celebrate the survey’s 70th year by checking out some of the ADS products now available.
- Downloadable PDF aerial survey quad maps from 2003 to the most recent year are available from the Us Forest Service, Pacific Northwest Region
- Interactive, web-based aerial survey maps and the 15-year cumulative mortality data product are available to explore: Look in the Forest Health folder on DNR’s mapping site.
- Historical aerial survey spatial data are available on the DNR website as downloadable GIS datasets (also known as “Bugs n Crud”) under Forest Disturbance
- 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 US 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: firstname.lastname@example.org.