The connection between forests and salmon populations

Published: June 7, 2019

Mountain River at Rocky Mountains, Alberta, Canada Photo by karamysh/Shutterstock

A fish without a tree is not as pointless as a fish without a bicycle, at least not when you’re dealing with salmon on Canada’s west coast. Research tells us that trees and salmon are good for each other in ways we might not first imagine.

British Columbia is home to five species of Pacific salmon: Sockeye, Pink, Chum, Coho, and Chinook. These salmon are anadromous, which means they hatch from eggs in freshwater streams and rivers, migrate to the ocean, where they mature into adults, and then return to where they started life, to spawn. This unique life cycle ties Pacific salmon to the health of the ocean and to the forests of Canada’s west coast.

Tom Balfour, project manager for the Central Westcoast Forest Society, a registered charity that works with partner organizations including local First Nations to restore salmon habitat on Vancouver Island, says that healthy forests support healthy fish populations. “Trees hold the stream banks together, provide shade over the stream, and create habitat for insects which the fish feed on. Then when big, old trees fall into a river they help to create pools and provide shelter and stable areas for fish to spawn.”

The salmon in turn provide essential nutrients that fuel the growth of forest ecosystems. As salmon mature, they migrate from the streams and rivers of their youth to the ocean, where they feed upon zooplankton, krill, and small fish. When adult salmon are ready to spawn, they migrate to the same freshwater rivers and streams where they were born. Upon their return, the salmon spawn and die, and “spread these marine-derived nutrients throughout the watershed, feeding the forest” says Balfour.

Because the salmon life cycle is so closely tied to the state of the trees surrounding spawning sites, changes to the forest can start a chain reaction that affects the health of fish populations. “Trees are a key component of most watershed processes. Early forestry practices had little regard for these processes, and harvests resulted in massive loss of freshwater habitat” says Balfour. Balfour says the biggest, easiest to remove trees were found along riverbanks, and when the trees were removed, the riverbanks began to unravel. Salmon spawning nests were filled with sediment, and rivers became wide, flat, and featureless.

Restoring salmon habitat that has been impacted by historic logging is a slow process. Balfour says it’s almost impossible to restore a site to what it was like historically. Instead, the focus is on creating habitat and speeding up natural recovery processes. “What will fully restore these watersheds is the recovery of old growth forests, but because that is such a long process and fish are doing so poorly, we must work to create what habitat we can while the system recovers naturally.” Tactics for habitat improvement include placing large woody debris and log jams in streams to increase habitat structures as well as planting native trees and shrubs.

If you own property on a fish-bearing stream and want to help Balfour says that ideally you should create a wide-forest buffer around the stream. If the property has disturbed habitat, consult a professional environmental company, to ensure that care is taken to maintain the health of the fish in the stream and the surrounding forest during the restoration process.

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