After the Fire

Potential debris flows in burned areas and how they actually can improve aquatic habitat. 
by Russ Plaeger, Bark Restoration Coordinator

Large, woody debris (re: logs and whole trees) are literally the backbone of our west side streams. Inputs of wood are essential to healthy functioning of aquatic ecosystems and typically happen as the result of windthrow, streambank erosion, fires, disease and mudslides or debris flows. The wood that will be delivered to streams in the gorge post-fire can enhance these streams. In fact, the earliest inputs of wood will hopefully lodge and get stuck in places where they’ll help to trap subsequent inputs of sediment. Gravels will be trapped upstream of the logs and will improve the spawning habitat for salmonids. Water flowing quickly over a log or logjam will help to scour out a pool downstream of the wood. The pools will provide important, deeper water habitat and will act as cold water refugia for salmon, adults and juveniles, during the hot summer months.

As happened post-Mount St. Helens some fish eggs will be buried, and smothered, by sediment that erodes into the streams in the gorge. But that’s one reason why salmon “stray” and thus some do not return to their natal stream. That evolutionary process helps to keep a local gene pool well distributed over the landscape so that literally not all of the eggs of a given population are in the same creek. Those that are in non-burn affected creeks (e.g. on the Washington side of the gorge or up or downstream of the burn) will survive and help keep a population going.

This is so awesome when you think about it; the ways in which the creeks we frequent, the streamside forests and the salmon have evolved together in such intricate, amazing ways over the eons. I get goosebumps just thinking about how far an 8 oz. juvenile Coho salmon travels from the Sandy or Clackamas before it returns as an 8 – 20 pound adult. Not something our bodies are capable of!

Spawning season is coming soon; the adults will begin moving further upstream as soon as there’s a freshet of rain to raise the water levels. Contact me if you want some suggestions re: where to go to observe spawning. It’s an awesome sight and even though I’ve been an up-close observer, sometimes within 6 feet of females digging nests in the gravel, I’m still in awe of how it all happens.

OK, you just got a download of some of what I learned during 13 years of working to restore salmon habitat prior to joining Bark. I hope it’s of interest!