Matt Provencher, Stewardship Forester, Washington State Department of Natural Resources, matthew.provencher@dnr.wa.gov
I’ve been fielding more and more calls related to wildfire risk in western Washington, and this only intensified after the past fire season.
In Washington, most wildfire efforts have focused on forests east of the Cascades. This makes sense, given the greater fire frequency and recent decades of catastrophic fires in that area. That said, western Washington forests are by no means immune to fire, and the hotter, drier summers occurring in the region means it will likely be something forest and woodland homeowners will need to consider more seriously.
With that in mind, let’s take a look at the ecology of wildfire in western Washington and discuss a few things you can do to prepare.
The 2020 wildfire season was indeed record-breaking in many aspects. The intensity of fire behavior observed, including extremely rapid rates of spread, is generally rare but something we know has repeated itself through history, and more frequently of late.
The fire ecology of wet, western forests differs greatly from that of drier forests in eastern Washington, but even westside forests have adapted to fire. One major difference between the two is the return interval, or the time period between fires in a given area.
Historically, in eastern Washington, this return interval may be on a scale of five to 30 years, depending on the location and some other factors; in western Washington, there is often 200 to 400 years between fires and can be up to 700 years for some habitat types, such as Pacific silver fir and mountain hemlock. This results in vastly different forest stand development. In eastern Washington, the frequent return interval leads to widely spaced trees and a relatively sparse understory. This sparse understory would burn frequently to perpetuate this condition, resulting in frequent low- to moderate-intensity fires that kill much of the understory, but most of the larger, fire-tolerant trees survive.
There are some places in western Washington where this may have also been the case – for instance, in rain shadow areas along south Puget Sound (like Joint Base Lewis-McCord). Indigenous peoples frequently burned these areas to maintain open conditions.
The vast majority of the forested area in western Washington, however, wouldn’t burn for centuries. This results in a biomass-rich and naturally heavy fuel load over time. Given the region’s significant precipitation levels and generally cool temperatures throughout the year, that fuel is generally not able to burn, or at least not capable of producing large fires.
However, every once in a while, conditions become ripe for rapid fire spread and we get what we call “stand-replacing fires,” or fires that burn so hot and intensely that they not only kill the understory, but also the majority of overstory trees as well.
Historically, intense fires like these in western Washington have required three conditions – an abnormally hot, dry summer, a dry east wind late in the season, and, of course, an ignition source.
This pattern has repeated itself throughout history and is responsible for some of the largest westside fires on record. Examples of this include the Yacolt Burn in 1902 or the Tillamook burns in Oregon in the 1930s. There is also evidence of massive fires (think millions of acres) in pre-recorded history. We experienced these conditions in 2020 but were fortunate to not have an accompanying catastrophic fire.
Though this is a natural pattern that would occur with or without climate change, most climate projections suggest summers will become warmer and drier with a possible lengthening of the summer season. These conditions alone are enough to conclude that the overall area burned in western Washington will likely increase. So, although we can expect more fire in the future, scientists do not yet know if the key ingredient for these terrible conflagrations, the east wind event, will become more or less frequent and intense. At best, scientists can say climate change “loads the dice” and increases the risk of these sorts of events. Examining future east winds under a changing climate is an active area of research in the scientific community.
So, what can we do about it?
In eastern Washington, thinning is the most important forest management tool for mitigating wildfire risk. Here in western Washington, there are numerous reasons to thin forests, aside from fire. Stand density management is critical to maintaining forest health in general. Given a changing climate, certain species will begin to struggle, especially on marginal sites (such as the Puget Lowlands, Olympic rain shadow and San Juan Islands), and forests in general will not be able to support the number of trees they have historically.
As these forests become overcrowded and, as a result, stressed, they are more susceptible to myriad threats, including drought, climate change, insects, diseases and, you guessed it, fire. Thinning can reduce the number of trees competing for the resources on the site – specifically light, water, and nutrients – and increase long-term tree vigor and resiliency to whatever threat they may face.
When thinking about thinning westside forests, I tend to focus on resiliency to forest health threats rather than preparing for, or mitigating the risk of, fire. Why? There are a few reasons.
First, western Washington forests are messy forests. Remember, there is a long return interval between fires relative to eastern Washington. Therefore, stands with a lot of brush, standing live and dead trees, and lots of downed wood becomes the norm for these forests over time. If you were to take a westside forest and thin, mulch, masticate, etc. to make it look like an eastside forest, you would be detrimentally altering the ecology.
Second, absent of frequent fires, it’s hard enough to maintain these open conditions in eastern Washington – could you imagine trying to maintain those conditions in western Washington, which has some of the most productive forests in the world and where some brush, especially our non-native and invasive species, can grow 6 feet or more in a growing season?
The third reason is that, given the best available science at the moment, thinning is unlikely to prevent or mitigate the kind of wildfire spread inherent to those large fires driven by east wind events, which spread far and fast through embers, creating complexes (not unlike the Camp Fire in California in 2019, or the Eagle Creek Fire in Oregon in 2017).
With regards to fire preparedness, forest management efforts are best focused in the areas described by Firewise USA® principles, primarily around homes and other structures. This is where we can have the greatest impact given the kind of wildfire we’ve been discussing.
The principles of defensible space can and should be used around structures or other high-value areas. This will help increase resiliency to fire without significantly altering forest ecology throughout your property, though it’ll still be a lot of work to maintain!
Shaded fuel breaks, where much of the brush and small trees have been cut and removed or chipped, can be used next to roads or trails where people or cars may start fires. Reducing the fuel in these areas not only prevents fires from starting, but also reduces fire intensity in case one does start. This may allow the road or trail to be used as an escape route or allow firefighters to use the area as a place to control the fire.
A final parting thought would be to pay attention to the weather forecasts. Wildfire scientists working in western Washington often refer to large fires here as “wind events with fire” because wind is such an important factor in determining fire behavior.
The east wind event in September 2020 was forecast well and a big red flag for wildfire agencies. One should take heed to do anything that can to reduce the risk of fire starts during these times. Reducing the use of power equipment, not mowing the lawn, keeping vehicles with hot exhaust off of fuels and other thoughtful measures can really go a long way toward reducing fire starts during these extreme weather events. Having an evacuation plan and emergency supplies ready at these times is also very important.
To learn more about western Washington wildfire ecology and the best areas to focus your efforts as a forest or woodland homeowner, watch this webinar from WSU Extension and DNR from June 2020. Fires have occurred in western Washington for thousands of years and will continue to occur into the future. Understanding the fire ecology, taking steps to reduce fuels in strategic areas of your property, and keeping an eye out for dangerous conditions can go a long way to reduce the risk to you and your property.
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