Species → Pink salmon
Pink salmon
Oncorhynchus gorbuscha
What if it disappeared?
Impact HighWithout salmon to carry marine-derived nitrogen into the rivers where they spawn and then die, leaves of trees near spawning streams would lose up to 22 to 24% of the nitrogen that today comes directly from them.
DocumentedDetail
Helfield, J.M. et Naiman, R.J. (2001). Effects of Salmon-Derived Nitrogen on Riparian Forest Growth and Implications for Stream Productivity. Ecology, 82(9), 2403–2409.
Using isotopic analysis, the authors trace the marine-derived nitrogen that salmon carry back into the streams where they were born and then die after spawning. Sitka spruce trees near salmon-bearing streams grow significantly faster than those near comparable streams without salmon.
Nitrogen input to riparian forests is markedly higher where bears and salmon are present together than where either species is absent.
DocumentedDetail
Helfield, J.M. et Naiman, R.J. (2006). Keystone Interactions: Salmon and Bear in Riparian Forests of Alaska. Ecosystems, 9(2), 167–180.
Bears drag salmon carcasses away from the stream to eat them under cover, leaving remains that fertilize a much wider area than dead salmon alone would reach in the water. It is the interaction between the two species, not either one in isolation, that produces the strongest effect on the riparian forest.
A sustained nitrogen input over decades could durably accelerate the growth of riparian forests and alter their structure — a plausible link, but one never tracked as a complete forest-scale phenomenon over that timeframe.
ExtrapolatedDetail
Extrapolation à partir de Helfield & Naiman (2001, 2006) : le raisonnement combine deux effets mesurés séparément à court terme, sans étude de suivi forestier sur plusieurs décennies.
If the extra growth measured over a few years persists over the lifespan of a forest stand, it could change the composition and structure of the riparian forest itself — but no study has tracked a forest over such a long horizon to confirm this.
What's missing to confirm it: No one has tracked a riparian forest over several decades to confirm that the extra growth measured in the short term translates into a lasting structural change.
Documentation
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Numbers and Biomass of Natural- and Hatchery-Origin Pink Salmon... in the North Pacific Ocean, 1925–2015 (Ruggerone & Irvine 2018, Marine and Coastal Fisheries)
Accessed August 10, 2026
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IUCN Red List — Oncorhynchus gorbuscha, statut de conservation
Accessed August 7, 2026
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Helfield & Naiman (2001) — Effects of Salmon-Derived Nitrogen on Riparian Forest Growth, Ecology
Accessed August 7, 2026
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Helfield & Naiman (2006) — Keystone Interactions: Salmon and Bear in Riparian Forests of Alaska, Ecosystems
Accessed August 7, 2026
Last verified: August 7, 2026