Salmon Grow Bigger Trees

Salmon spawn tree growth, healthy forests benefit salmon, a new study shows.

It's Mother Nature's version of "I'll scratch your back if you scratch mine." Researchers studying rivers in Alaska have found that salmon and forests help each other out. Riparian forests keep streams how salmon need them-cool and clear-by providing shade and stabilizing riverbanks with their roots. Salmon, in turn, give critical nutrients back to the surrounding vegetation when they die.

Tracing a heavy form of nitrogen most abundant in marine environments, scientists from the University of Washington, Seattle, were able to measure the amount of nitrogen in freshwater streams that originated in the ocean. They found that this heavier form made up nearly a quarter of the nitrogen in trees and shrubs along salmon streams, and that these plants grew more than three times faster than vegetation along the banks of salmon-free waters. For example, Sitka spruce, which may take up to 300 years to reach 50 centimeters in diameter, take an average of only 86 years to thicken up along salmon streams.

Male sockeye salmon
Male sockeye salmon.
Photo: Jeremy Sarrow and Dave White
Wenachee River, Washington
Wenachee River, Washington.
Photo: Sherry Ballard, CalAcademyCollection.

Salmon, which spend most of their lives in the ocean, migrate to freshwater streams to spawn. After spawning, they die and their nutrient-rich bodies fertilize the water. Flooding rivers also wash some carcasses onto riverbanks, while animals such as salmon-loving bears drag fish into the forest interior.

The study emphasizes the connected nature of nature and suggests that forest and fish management should be unified.

Salmon fry
Salmon fry find shelter in river edge tree roots as well as fallen trees and rocks.
Photographer: Unknown, CalAcademyCollection.