"It's Complex" Fire Ecology & Recovery 2015 Conservation Course - Class #3 Notes

Summary of Feb 10, 2015 class by volunteer Nick Thorp

Right not, as the Methow experiences abnormally warm temperatures and rain in the middle of winter and sees the rivers and creeks rise, the topic for the 3rd week of the Conservation Course coincided well with the weather as it explored the impacts of the fires on fish.  Fisheries biologist Jennifer Molesworth joined the group this week to present on the subject and provide insights on the potential effects the Carlton Complex fires may have on the various fish populations of the Valley.

The watershed of the Methow Valley is roughly one million acres in size, stretching from the Canadian border to the confluence of the Methow and Columbia Rivers in Pateros.  The rivers, creeks, and lakes that make up our watershed provide habitat for a variety of fish species, with the most well-known including: spring and summer Chinook salmon, steelhead and rainbow trout, westslope cutthroat trout, Pacific lamprey, sculpin, and whitefish.  Just like the plants and trees we learned about during the previous weeks, the ability of these fish to recover from disturbances like fire is based on various factors that allow them to be resilient.

From a historical perspective, fish have been bouncing back from disturbances like fires and landslides for thousands of years.  While the immediate effects of fire (and debris flow) can include high mortality rates on fish populations due to high water temperatures, turbid waters, and related conditions; in the longer term, the effects of fire and related landslides and debris flows generally include improvements to fish habitat, and fish populations often increase in size in the first few years following fire. Two of the main reasons for this response are habitat creation and nutrient loading.  

After the fire, many creeks and rivers flooded and eroded soil

As fires burn through an area, trees and woody debris make their way into the rivers and creeks both through dead trees falling over and landslides carrying them in.  These materials in the river, provide cool, shaded habitat for fish. With landslides and debris flows in the mix, new pools are created, rivers and creeks forge new channels, and the diversity of habitats for fish can expand.

The second impact of fire that can aid fish in a strong recovery is nutrient loading.  Just as trees and vegetative debris that enter the water create habitat, they also bring with them large amounts of nutrients. In the right amount and diversity, nutrients can help boost the growth of algae that serves as the basis for the food web and supports the ecosystem of rivers and streams.

The big question of course is: with the size and severity of the Carlton Complex fire, how quickly will the fish bounce back? According to Jennifer, as with all things related to the fire…it is complex.  The high intensity of the fire that spiked water temperatures, the large amount of ash that flowed into rivers and creeks during the intense rains after the fires, and the severity of the debris flows all contributed to fish mortality during and following the fires.  These will also make it harder for fish to bounce back.  Luckily, the fish who survived the fires because they were not present during the fires or the floods can recolonize the streams in the burned areas, especially since undersized culverts and other fish barriers have mainly been addressed by past restoration projects.  The

Some debris flows were over 8 ft high

re-colonizing fish will gain from the longer-term habitat and nutrient-input benefits from the fire and debris flows.

There are also other factors working to the advantage of fish. One is the location of fish during the fire event.  Many of the year classes of salmon and steelhead were out at sea during the fires and flooding and so missed the excitement.  For those that were in the Methow, some anadromous species, such as spring Chinook, were already up valley away from the direct impacts of the fire and debris flows.  Secondly, while the debris flows dumped high loads of sediment into our rivers and streams, we’ve been experiencing a mild and wet winter with river levels and flows that has been helpful in clearing out that sediment.  The more that is cleared, the more opportunities for fish to find good habitat conditions as they travel up and down the rivers and creeks.

While with all things of fire recovery, time will tell.  Disturbances like fire, flood, and debris flows are important for renewing habitat conditions in the long-term.  Overall, estimates for impacts on fish, taking into consideration both the positives and negatives, may turn out to be neutral or positive.  The resiliency of fish, vegetation, and of nature in general have allowed them to bounce back before.

All these classes are being videoed!  Watch the classes online at our website here:
http://methowconservancy.org/conservation_course_2015_videos.html