Washington State Department of Natural ResourcesEvery year since 1947, an insect and disease aerial detection survey is conducted across all forested lands in Washington state by the Washington Department of Natural Resources in cooperation with the USDA Forest Service. In practice, two aerial survey specialists positioned on either side of a high-wing aircraft sketch-map forest damage on tablet computers on a 4-mile grid 1000+ feet above the terrain. Recently killed and defoliated trees are recorded, building a historical record of forest health trends. Most of the mortality observed is caused by known insect and disease agents, although trees killed or damaged by abiotic events such as winter storms, wildfire, flooding, and landslides are also recorded. Defoliation damage presented in this dataset is active whereas mortality is passive as it typically takes a year or more for afflicted trees to exhibit the characteristic symptoms of decline (i.e., bright red, orange, or yellow foliage). Generally speaking, defoliation data is measured the year it occurs, and mortality data represents insect and disease activity that took place a year prior to the date it was recorded. Likewise, trees killed in a given year will not show in aerial survey data until the following year. Only trees displaying the distinctive colors and patterns of recent decline, otherwise known as "damage signatures," are documented. For example, when bark beetle damage is observed, a polygon is drawn on a digitized map denoting the location and range of the damage. Polygons are then given a shorthand code suggesting the most likely damage agent (e.g., code: 6L for mountain pine beetle in lodgepole pine) and a relative severity percentage of affected trees within. Trees that have been dead over a year appear white or grey and are excluded from these assessments. Surveyors choose from five damage severity categories when creating polygons: Very Light (1-3%), Light (4-10%), Moderate (11-29%), Severe (30-50%), and Very Severe (>50%). These five damage severity categories are then recalculated into "trees per acre" (TPA) estimates to remain consistent with historical WA DNR aerial detection survey datasets and reporting. Note: the causal agent of forest damage and mortality is an educated guess. Post-season ground surveys are implemented to validate observations made by aerial survey personnel and serve to reinforce accuracy as remote-sensing specialists. No vertical data is recorded.ArcGIS DynamicMapLayerhttps://hub.arcgis.com/datasets/73af448b66a04cafac99ed721c0116cf_2engState of Washington Geospatial Open Data PortalPublicAbiotic/Animal/Root Disease [Washington (State)]Web servicesWashington (State)Last Modified: 2025-08-25