In Washington’s nearly 22 million acres of forests, how in the world do you keep track of the culprits that kill trees? The culprits in this case are disease and insects. Dead trees can lower the value of timber products, affect important habitats and change the ecology of forests. When trees are dead or dying, they can be easy fuel for spreading wildfire and may increase potential for catastrophic wildfire impacts.
Forest health aerial survey and analysis
DNR and U.S. Forest Service scientists have just completed an aerial survey of the forests throughout Washington to find any new tree mortality that has occurred during the last year. The goal is to document annually the number and location of dead or defoliated trees and what caused their decline. Study of the survey, in turn, helps forest health scientists identify why problems are occurring. DNR’s Forest Health Program scientists look for patterns of damage in the crowns and roots of individual trees and across stands of several trees.
Each year, the data are compiled into summaries and mapped so those who don’t have access to a comprehensive birds’ eye view of the forest can see what the insect and disease specialists in the airplane observed. In 2009, almost 6.4 million trees were recorded as recently killed. The 2010 numbers currently are being compiled, but each year we use the data to complete a Forest Health Highlights report.
How the information can be used
Landowners can use the information to understand which insects or diseases are active in the vicinity of their property and manage their forests, using strategies that are needed to reduce vulnerability. This may include thinning the forest, removing the weakest trees so remaining trees have sufficient water, light and nutrients to vigorously resist new damage or recover if injuries occur.
What causes trees to be more susceptible to disease and bugkill? Often native insects and diseases thrive when trees are weak and crowded, so insects or fungi are able to move easily from susceptible tree to tree. Sometimes severe weather events injure or kill tress. These events include drought, wind, freezing, heat stress, flooding, landslides and hail.
Aerial surveying is just one method to gather information on the health of Washington’s forests. On the ground surveys in areas of particular interest then can examine and evaluate tree health close up. These surveys provide early warning of pest epidemics that can kill forests, raising wildfire risks. DNR’s Forest Biomass Initiative also seeks to reduce the loss of trees and other forest resources to pest and disease outbreaks.
Aerial insect and disease surveys show where trained DNR and Forest Service observers have noted newly killed or defoliated trees. Each spot noted on the maps is labeled with a damage code and a severity rating (High Moderate or Low) or the number of trees affected. Codes for the damage agents – insects, diseases, weather, etc. — are described in a legend at the bottom of each map.
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