This is not a joke: the salmon do indeed grow the forest.
A natural fertilizer
It's an incredible story that happens in the river Allier, one of the main tributaries of the Loire, where Atlantic salmon are not very numerous. The 400 or so "survivors" who have been surveyed manage to cross the ocean, to walk up the water with all the dams that stand on their way, and that for nearly 1,000 kilometers away. Their terminus, in Haute Loire, is their spawning area, in fresh water, where they lay their eggs.
Recent studies show that when salmon die, after laying their eggs, they become useful to the forest, which extends on the banks. Because indeed, salmon boost the growth of trees, making them a kind of natural fertilizer. Only in France, this phenomenon is not really noticeable on the forest since wild salmon are not very numerous. But these are still very numerous in North America, or even in British Columbia.
When bears get involved ...
When big predators intervene, it totally changes the situation. Bears, for example, can play a major role in the interaction between salmonids and forests. By going fishing, a bear is able to bring up to 30 kilos of salmon a day on the banks, or even beyond, into the deep forest. Half-eaten salmon carcasses release during the decomposition process a number of nutrients, including nitrogen and phosphorus. It is precisely these nutrients that will activate the growth of trees.
This is one of the reasons why the forests of western Canada are so lush, to thank the salmon.
This example, among many others, illustrates the interconnectivity between fauna and flora, and generally between all living things. An example of the "magic of nature" that shows us once again that everything is connected in this world and this biosphere, of which we are part.