Annual Summary of Insect and Disease Activity in Washington Released

By Glenn Kohler, Forest Entomologist, Washington State Department of Natural Resources,

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.

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

Healthy Habitat Piles — Or, Being Down With Downed Wood

Ken Bevis, Wildlife Biologist, Washington State Department of Natural Resources,

Providing habitat complexity is the best way to ensure diverse and rich wildlife populations on our forest lands. Dead and down wood, including small pieces, are key elements, and through active management we can provide much of this habitat.

Many species of wildlife utilize dense collections of woody material in shrub patches or down wood concentrations. Birds, such as song sparrows and juncos, mammals, including snowshoe hares and chipmunks, reptiles like garter snakes, or amphibians like salamanders or toads will rest and breed in the relative safety of the complex network of twigs, logs and leaves in these habitat features.

Forestry offers numerous opportunities to maintain and even enhance this habitat.

Thinning and harvest activities always generate considerable quantities of woody and green material that must be dealt with in some manner. Choices for slash management include leaving it where it falls, burning (piles or broadcast), lop and scatter, chipping, or constructing and retaining habitat piles.

There is incredible habitat value with piled material. In fact, creating a loose pile of slash, using logs and branches, may be the fastest known way to create beneficial habitat structure.

The insect fauna of our forest ecosystems is varied and complex.

The vast majority of insects do not pose problems for forestry, and often perform useful ecosystem roles such as nutrient cycling or preying on populations of other insects. “Bad bugs” are generally considered those that defoliate trees to an excessive degree or consume cambium, which can cause tree death.

Despite the understood value of piles for habitat, there is discussion, even debate, over the risk of increased populations of “bad bugs” in these piles.

The good news is that the risks are largely restricted to management of pines in drier forests of Eastern Washington. Rob Lionberger, the DNR Stewardship Forester for the region, cautions leaving any pine slash less than six months old on the ground between April and September. This quote form Melissa Fischer, DNR’s forest pathologist for Eastern Washington explains why:

“We have been seeing a change in the pine engraver’s life cycle the past several years.  Historically, the pine engraver had 2.5 generations per year (i.e. from egg to larvae to adult laying eggs). Recently, there has been a full third generation. This elongates the time period where you would not want to leave pine slash/ logs on the ground. I consider October-December as the low-risk time period, July-September as medium-risk and January-June as the highest-risk time periods.”

Basically, if small-diameter material is created during that late summer to early winter period, the cambium will have time to dry out and no longer host the beetle for extra life cycles. However, a large-diameter tree (think more than 8 inches) with intact bark harvested during that time will not be able to dry out before the beetles fly in the spring.

In other words, play it safe by building your habitat piles with small-diameter materials harvested between October and December. Also, materials from other species that do not harbor “bad bugs” (willow, for instance) can be used in piles any time of the year.

Western Washington’s wet forests also have a variety of insects hoping to feed on the cambium of live trees.

However, in this region they require large amounts of recently dead, large-diameter wood (think of a big windstorm) to build populations that can significantly impact a stand of healthy trees nearby. As a result, insects are rarely a major forest health issue on the west side and are generally considered “secondary” pests.

In Western Washington cutting small-diameter materials (8 inches or less) for habitat piles will usually not result in increased insect populations, regardless of timing.

ken bevis does matisse impression
Side view of a habitat pile with larger materials on bottom and fine materials layered on top, including a perch for birds. (Illustration by Ken Bevis, DNR)

I recommend having at least two habitat piles per acre, especially in areas of active management. This provides adequate wildlife habitat but does not amount to enough woody debris to be a serious wildfire hazard.

The habitat piles can be constructed by hand, placing larger materials on the bottom several layers deep and covering with finer materials on top. These should be at least 10 feet in diameter and 5 feet high, to provide some interstitial space for small animals to get inside.

Be creative and consider what might be able to live there. Make an entrance big enough for a bobcat or coyote. Layer small logs and branches into a roof on the third or fourth layer to provide dry cover in wet winters. Build the pile around an existing shrub. Old slash piles often have shrubs growing out of them and provide excellent habitat. You will be amazed how much use they get, especially from smaller wildlife.

Send me pictures of your best habitat piles! But don’t feed those bad bugs …

Announcements, Events, and Other News

2019 Forest Owner Field Days

The annual Family Forest Field Day attracts hundreds of landowners from all around the region to learn about a variety of forestry topics in a hands-on setting, including forest health, wildlife habitat and management, thinning and pruning, chainsaw safety, noxious weed management, and more.

Deary, ID – Saturday, June 22 (registration open)

Arlington, WA – Saturday, August 10 (details coming)

McCleary, WA – Saturday, August 24 (registration open)

Forest Health and Wildfire Seminars

Learn what makes forests healthy or unhealthy and how to recognize when there’s a problem on your property. Topics include insects, diseases, and drought, including their environmental roles and the important interactions between them. Learn about what property owners should do (and not do) to increase tree resilience and mitigate impacts.

Forest Stewardship Coached Planning

If you own wooded property, our flagship course will teach you how to assess your trees, avoid insect and disease problems, and attract wildlife. State experts will help you develop your own Forest Stewardship Plan to keep your woods on track to provide enjoyment and income for years to come.

  • Preston – Tuesdays starting September 10
  • Vashon – Mondays starting September 23
  • Cowlitz County – Location and details TBD

Other Events

Hands-On Chainsaw Safety and Maintenance Workshop – Okanogan, June 21-22

Can’t find the event you were looking for? Visit or contact

A Rotten Story: Forest Decomposition

The woods can be pretty messy, with all of those leaves, branches, twigs and logs falling over and cluttering up the forest floor, making it hard to walk around.

What is Mother Nature thinking? Oh wait, now where does soil come from? Do these organic inputs actually help fuel the amazing and rich forest ecosystems we nurture, exploit, and enjoy?

Douglas-fir log subject to fungal work in Eastern Washington (Photo: Ken Bevis)

According to U.S. Forest Service research, one acre of managed conifer forest in Washington averages around 107 tons of above-ground organic material at any given time (Campbell et al. 2010).  In the lush, west-side timberlands Douglas-fir and hemlock/spruce forests often contain 300-450 tons per acre, and this doesn’t even count what is below ground!

Photosynthesis and growth are continuously adding material to this system by pulling carbon dioxide out of the atmosphere and creating tissue through this amazing, miraculous process. This material continuously builds up, and we might wonder, why aren’t we simply overwhelmed with old tree and plant parts? A complex ecosystem under our feet breaks all of this material down and turns it back into basic components that recycle and feed the system.

Most of the essential break-down work is done by fungus. Yep, good old fungus.

In fact, the moist forests of the Pacific Northwest are a great kingdom of fungus, with enormous biomass of fungal life all around us. Kneel down and pull apart some of the forest duff and rotting wood. See the white threads of fungal mycelium down there? These tender “roots” are the main body of fungus, and move through the downed material, breaking it down to basic components using enzymes and other chemicals. The fungus uses some as food and nutrients, processes it again, and releases further broken-down material that is picked up by the next organism in the soil ecosystem.

There is a zone called the “rhizosphere,” which refers to the immediate area around roots and root tips, where a high degree of the biological activity in the soil occurs. Here, fungus, bacteria, nematodes, springtails, worms and many other organisms interact with each other and the plants to support the forest (Molina & Amaranthus, 1990). Sometimes, nitrogen (a limiting nutrient in soil) is pulled from the atmosphere and “fixed” by nodules of bacteria attached to the roots of plants, including alder. The alder doesn’t do it, the bacteria do. An amazing example of symbiosis.

It gets even more complicated …

There are also mycorrhizal fungi. They form an essential symbiotic relationship with plants by attaching to root systems with fungal hyphae (threadlike fungal “roots”). These help the plant by absorbing moisture and nutrients. In return, the fungus gets sugar from the plant’s photosynthesis. This is an amazing relationship that is being rigorously studied, and is now known to be critical element of a healthy forest.

Mushrooms on the forest floor near Sequim, Washington. (Photo: Ken Bevis)

And don’t forget the mushrooms. Most of a fungus is in the form of hyphae, invisible above the ground, performing the quiet, unglamorous work of digesting organic material. But when conditions are right, the fungus needs to reproduce, mix genetics and spread their growth around, the mushrooms appear.

Mushrooms are the fruiting bodies of fungi. These can provide food for a variety of forest-dwelling animals, including the northern flying squirrel, which then spreads the spores through their droppings and help the fungus move about the forest.

Some of these above-ground fruiting bodies are tasty to us homo sapiens too, including chanterelles, matsutake, and morel mushrooms. Some fungi have below-ground fruiting bodies, such as truffles, but the effect is the same. These “fruits” are often meant to be eaten by something to help spread the fungal wealth in the ecosystem.

Forest floor duff near Adna, Washington (Photo: Ken Bevis)

Fungi are the “engines of decay” in the forest ecosystem, beautifully described in David George Haskell’s excellent 2012 book, The Forest Unseen. Haskell looks closely at one square meter of a Tennessee forest over the course of a year, and shares observations of life, both large and small, that apply to forests everywhere.

Meanwhile, glamorous megafauna such as our banana slug, will eat fungal elements, including mushrooms, and can play their own role in breaking down organic material by shredding, eating, and defecating as they slide around the forest floor (see recent article in DNR’s Small Forest Landowner News).

There are a lot of other animal characters acting in the forest duff as well, including mites, millipedes, centipedes, springtails, protozoans, worms, spiders, snails and gophers. The food chain down there is stunningly elaborate, with fungus (and bacteria) in foundational roles, breaking leaves and wood down initially in a myriad of ways. Then small animals such as springtails, (some smaller than the period at the end of this sentence!) feed on the fungus and the released compounds. These critters are in turn fed upon by larger creatures such as millipedes, who are in turn fed upon by larger critters, such as shrews, who could be eaten by a small owl, who could be eaten by a larger owl or coyote, etc. It is boggling when the various energy pathways are identified.

Forest floor megafauna – Red-backed salamander. (Photo: Ken Bevis)

Salamanders live in the decaying duff and wood of the forest floor. These ancient life forms live slow and deliberate lives, mostly in the dark tunnels underground, making dramatic appearances on wet days in our forests. They eat small insects and worms, and are the apex of the rotting wood food pyramid.

How our forests are managed can greatly influence what happens in the soil. The soils we began managing in the late 19th and 20th centuries were the products of many thousands of years of development by way of fire, ice, geology, organisms and time. Human impacts in forestlands today are generally in the form of changing vegetative structure, removing organic material and soil compaction.

What can small woodland owners do to help promote and protect the precious habitats and soil ecosystem below our feet? A few suggestions:

  1. Retain organic material across the land, especially decaying logs
  2. Keep portions of the land shaded to lessen soil drying
  3. Minimize compaction from machinery
  4. Scatter large organic pieces after harvest
  5. Retain patches of natural forest at regular intervals on managed landscapes to enable soil flora and fauna to persist and return to managed areas
  6. Get down on your hands and knees with a hand lens and marvel at the life in a patch of duff, rotting wood, and forest soil


This is only the proverbial tip of the soil ecosystem. I hope you got down low on the forest floor, looking under some duff with dirty hands after reading this article. Send me your photos, ideas and experiences!

Ken Bevis, Wildlife Biologist, Washington State Department of Natural Resources,


Campbell, S.; Addell, K.W.; Gray, A.; (2010). Washington’s forest resources, 2002-2006: Forest inventory and analysis report.  Gen. Tech. Rep. PNW-GTR-800.  Portland, OR: U.S. Department of Agricultur, Forest Service, Pacific Northwest Research Station.

Molina, Randy & Amaranthus, Michael. (1990). Rhizosphere biology: ecological linkages between soil processes, plant growth, and community dynamics.

Helping Landowners Learn From Their Peers About Harvest Options

Northwest Natural Resource Group and Oregon State University are reaching out to forest owners for a voluntary study about timber harvesting methods to understand how they affect both financial and forest health outcomes.

The goal of this research project is to help landowners who are considering a timber harvest to learn from the experiences of others. There is limited information about the economics of commercial timber harvests that use thinning or uneven-aged management, and how those results compare with other harvest methods.

The researchers are looking to survey Oregon and Washington forest owners who harvested timber from their forest in the past five years (since 2014) and are willing to share information about the silvicultural methods and financial outcomes from these recent timber harvests. The survey asks detailed questions about the harvest techniques and equipment used, the volume of timber harvested, cost of the harvest work, and the harvest revenues.

The results of this study will be shared with forest owners through a variety of methods including articles, papers, and classes taught by NNRG, OSU, and partner organizations. Data in the study will remain confidential within the research team. Information will be aggregated so it cannot be traced to any individual ownership. Data will be collected from through June 2019.

If you are willing to share recent harvest information with NNRG and OSU, contact Lindsay Malone, one of the project researchers, at Lindsay can provide you with a copy of the survey.

Learn more about this research project at

Lindsay Malone, Director of Programs, Northwest Natural Resource Group,