Flowing Fishes to Forests
While forests depend on nutrience from the ocean, freshwater fish bring it with them when they return to their birthplace, in their death throes.
Introduction
After gathering biomass in the vast ocean, salmon return to their freshwater birthplaces, bringing with them nutrients from seawater. These are essential to the ecological lifecycle of many forests.
They reduce their feeding activity and use up all their energy when swimming upstream against the strong current. Their bodies become the "nutrient pumps" of the ecosystem. Once they are done spawning, their bodies keep deteriorating until death.
Their post-spawning carcasses, rich in nitrogen, phosphorus, and carbon, serve as a veritable feast for a variety of organisms. It's estimated that up to 70% of the nitrogen a riparian (riverbank) forest needs can come from these spawning salmon.
The forest's nutrient cycle doesn't stop at the water's edge. Bears and birds, the unsung heroes of this tale, play a significant role in transferring these nutrients from the water to the land.
In Alaska's Kodiak National Wildlife Refuge, bears transport between 50% and 70% of the salmon they catch into the forest. They can carry salmon up to 150 meters from the river, effectively fertilizing the forest with salmon-derived nutrients.
The result? Trees that use salmon-derived nitrogen grow three times faster than those that don't.
Role in Forest Growth
A 2002 study published in the journal "Nature" found that up to 24% of the nitrogen in the foliage of trees near salmon-spawning streams in Alaska and British Columbia came from marine sources, i.e., the fish.
This percentage was lower farther from the streams, showing that the fish's nutrients had a direct impact on the trees' growth. But this delicate balance is under threat. Salmon populations are under signficant risk of declining, due to overfishing, habitat loss, and climate change pose. A 2015 study published in the "Journal of Animal Ecology" found that reductions in the number of salmon returning to spawn could have significant long-term effects on the growth and sustainability of these riparian forest ecosystems.
Conclusion
Salmon are crucial to the health of forests and the nutrient cycle. Their decaying bodies after spawning provide nitrogen, phosphorus, and carbon that fertilizes riverbank forests. Bears and birds spread these marine-derived nutrients far inland, but declining salmon populations threaten many risks to the ecosystem at large. Further action needed to protect the crucial role of salmon in sustaining the life-giving cycle of our planet.
Actions
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Read on to learn more about the unexpected and wondrous ways that animals contribute to ecosystems.
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