The Salmon-Bear-Forest Connection: Nature’s Circular Economy in the Pacific Northwest
Recently, we relocated to British Colombia in the Pacific North West. Its a place of truly epic and inspiring natural beauty. Its also a place where the great cycles of nature are on show. I have been looking forward to observing one of these cycles and I have been regularly checking the creeks and the nurseries in our local area. Then the Salmon appeared, slowly at first, but soon there were thousands and its still going 8 weeks later.
The Salmon are here to spawn in the waterways where they born 4-8 years ago, but they are also playing a much bigger part than they are aware. In the lush rainforests of the Pacific Northwest, there’s a surprising yet essential connection between salmon, bears, and trees. While it might seem strange that fish could help sustain towering forests, these three elements create a unique ecosystem dynamic, highlighting the delicate balance and interconnectedness of nature.
As an environmental engineer, learning about this cycle has reminded me of what we as engineers are often aspiring to create; a circular economy. The relationship between salmon, bears, and forests in the Pacific Northwest is a beautiful example of nature’s own version of a circular economy. Each species and process in this ecosystem contributes to a sustainable cycle where resources are used, repurposed, and recycled in a way that benefits the entire system. There are of course many examples of these systems in nature, which have allowed such beauty and complexity to thrive for so long. Unfortunately human engineered systems are far out performed by nature and the issues of growth, waste and the quest for more material are central to our times. We have a long way to go, but nature has found many ways and we should take inspiration. This is the story or the cycle that I have witnessed unfolding in my neighbourhood.
The Salmon and the Sea: The Source
Each year, salmon make an incredible journey, swimming upstream from the ocean to spawn in the freshwater rivers and streams where they were born. This journey doesn’t just ensure the survival of their species; it also brings a wealth of nutrients from the ocean into inland ecosystems. Salmon carry marine-derived nitrogen, phosphorus, and other nutrients within their bodies. When they return to spawn, their life cycle comes full circle as they die shortly afterward, releasing these nutrients into the water and surrounding environment.
The lifecycle of a salmon begins as eggs laid in freshwater streams, where they hatch into alevins, nourished by their yolk sacs. They grow into fry and later parr, feeding in their freshwater habitat until they become smolts, adapting to saltwater as they migrate to the ocean. In the ocean, they mature, feeding and growing for 1 to 5 years, depending on the species. Once mature, they navigate back to their natal streams using an extraordinary sense of smell and environmental cues.
The Bears: The Distributers
Bears, particularly grizzly and black bears, play a pivotal role in spreading these nutrients throughout the forest. Salmon are a major food source for bears, and as they catch them from rivers and streams, bears often carry their prey deeper into the forest to eat. Bears are the ultimate picky eaters and only consume the most nutrient-rich parts, like the brain, skin, and roe, leaving behind other parts that decompose into the forest floor. This leftover fish material, rich in nitrogen and other nutrients, seeps into the soil, nourishing the surrounding ecosystem. An adult black bear at this time of year whilst getting ready for a winter hibernation can eat up to 20,000 calories a day, which could be upwards of 20 fish a day!
By dragging salmon away from waterways, bears act as natural nutrient distributors. Research shows that this behaviour can spread salmon nutrients up to 500 meters away from rivers, enriching trees and plants well beyond the riverbank. Other animals, like wolves, foxes, eagles, and smaller mammals, feed on the remains left by bears or catch fish themselves. As they consume and transport parts of the fish, they spread nutrients further into the forest. Even invertebrates and fungi contribute by breaking down fish remains, releasing nutrients that seep into the soil and are absorbed by plants.
The Forest: The Result
The trees and vegetation in the Pacific Northwest rainforests are often starved for nutrients. Despite the dense foliage and lush landscape, the soil here tends to be thin and nutrient-poor due to heavy rainfall, which washes away essential minerals. The marine-derived nutrients from salmon make a tremendous difference, boosting tree growth, soil fertility, and the overall resilience of the forest. Without the salmon and bears the forest in the coastal areas would need to rely on ocean storms and mist to deposit salts and other trace nutrients. Additionally, nitrogen from atmospheric sources, such as lightning, can be deposited into the soil, providing a natural nutrient boost even in areas far from rivers.
Studies analysing tree rings have shown that salmon nutrients—particularly nitrogen isotopes—can be detected in trees hundreds of meters from the streams. These nutrients help trees grow faster, stronger, and more resistant to disease and environmental stressors. Some trees, like Sitka spruce, can grow up to three times faster near salmon-rich streams than those without salmon nutrients, showcasing the profound impact of this nutrient cycle.
Once these nutrients are in the forests they are recycled through a decomposition process, aided by fungi, bacteria, and insects, sustains nutrient availability and helps plants to grow. Forests support this nutrient cycle by providing bears with cover, suitable habitats, and tree cover along riverbanks that helps regulate water temperature and quality, which salmon need for spawning.
Conclusions
The salmon-bear-forest relationship is a masterpiece of nature's circular economy, developed organically over millennia. Each element in this system fulfils multiple interconnected roles, ensuring that nothing is wasted and that all materials are repurposed to sustain life. Salmon bring marine-derived nutrients upstream, bears distribute these nutrients across the forest, and trees absorb them to support their growth, while also providing shade and stability to salmon-spawning streams. Even in death, each organism enriches the ecosystem, fuelling countless cycles of renewal. This intricate balance has evolved over deep time, driven by the pressures of survival and the inherent efficiency of natural processes. It demonstrates how ecosystems can function as fully integrated systems, where the output of one process becomes the input for another, creating a closed-loop of energy and material flows. Each waste is repurposed into something beautiful.
When compared to human attempts to create a circular economy, the gulf in complexity and efficiency becomes apparent. There are good examples such as the recycling of paper, steel, copper, glass, textiles and aluminium that are well established, but we are far from creating systems as complete and self-sustaining as those found in nature. Nature sets a standard that is in all intents and purpose impossible to meet, so what can we achieve? This is huge topic of discussion, but some questions I have are;
Just how circular can we ever realistically be?
Where are the opportunities?
What do we do with those materials that don’t fit into these systems?
By focussing on one issue, do we do so at the expense of others?
Growth vs sustainability - how can we improve this relationship and what are the limits?
