With most conifer trees in the region like red cedars, the main limiting growth factor is nitrogen, which is used to create chlorophyll, which they use to photosynthesize, creating Oxygen and sugars from CO2 and sunlight that allow them to grow big and strong. But nitrogen is pretty tough to come by in a usable form in terrestrial environments like this, and is often sourced from decomposing leaf litter of deciduous plants and trees that’s broken down by fungi and insects and distributed with the help of various mycorrhizal fungi.
Yet here, in riparian areas of streams that support salmon, there are unusually high levels of Nitrogen 15 and Carbon 13, which are rare stable isotopes primarily found in the oceans. Turns out that these salmon, after spending their adult lives in the oceans, return up these rivers to spawn and when they die, their carcasses are carried off into the woods by bears and other predators where they decompose and are carried even further into the forest by birds and other scavengers, and when they break down or find their way back to the forest floor through scat from whatever has eaten it, they leave those rare isotopes of Nitrogen and Carbon in the soil, redistributing these important nutrients all throughout the forest so that trees like this cedar here can grow big, strong and healthy.
Studies of these trees show higher than usual concentrations of these rare oceanic derived nutrients deep in their heartwood, suggesting a relationship between these fish and forests that goes back thousands of years, so without these salmon, the iconic forests of Cascadia wouldn’t exist as they do today.
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