Coastal rainforests: Unlocking the mysteries

In the still-pristine valleys of British Columbia’s north coast, biologist Dr. Tom Reimchen is documenting the complex relationship between the well-being of the temperate rainforest and healthy populations of salmon, grizzly and black bears.

Dr. Reimchen, of the University of Victoria, BC, has discovered that a heavy nitrogen isotope called N15, which is found only in the deep waters of the Pacific Ocean, appears in the growth rings of trees in the coastal rainforest.

How did it get there? He concludes that when spawning salmon return to BC coastal rivers, they carry in their bodies large amounts of carbon and nitrogen, gathered during their years in the Pacific Ocean. Bears catch and devour the salmon, bringing the nitrogen-rich fertilizer into the forest.

Dr. Reimchen has observed bears fishing in coastal streams and rivers. They drag the salmon into the forest – as far as 100 metres from the river – and often eat only part of the fish. Other animals, insects and birds then feed on the remaining carcass, distributing this rich source of nitrogen throughout the forest. This research highlights the importance of abundant salmon runs, and offers yet more proof of the essential role every species in order for an ecosystem to be healthy.

Visit Dr. Reimchen's lab

View a short video of the rainforest, featuring an interview with David Suzuki