Salmon in the Forest
Story by Mark Hume with Photography by Nick Didlick
Salmon are the base of everything in the Pacific Northwest.
Fishermen have known that intuitively for a long time, but now it has been confirmed in a set of studies from salmon ecology researchers at Simon Fraser University, in British Columbia.
In one of the largest field studies on salmon in the world a team led by, Morgan Hocking, a postdoctoral fellow, and John Reynolds, the Tom Buell B.C. Leadership Chair in Salmon Conservation, looked at 50 watersheds in the Great Bear Rainforest.
The region, on B.C.’s Central Coast, is a largely protected area that still holds some of the last untouched old growth forest in North America. It is mostly without roads, and the research team went there to look at how salmon runs impact watershed vegetation.
What they found is that the salmon carcasses dragged out of the water by bears, wolves and other animals, change the nature of the surrounding forest.
The change is so dramatic, said Mr. Reynolds in an interview, that it is possible to tell how rich a salmon run is by looking at the forest makeup along the stream.
Before we started the study I would have thought that was a real long shot. But now I think we could do that,he said. The impacts of salmon on plants are so radical that, even without knowing how many salmon spawn in specific streams, we can get a good idea by studying the surrounding plant life.
The study found that plants that are good at picking up nitrogen, which filters into the soil from salmon carcasses, thrived along streams with large salmon runs. Those plants that weren’t as good at absorbing those nutrients, were pushed out of the area.
The shift in dominance of some of these plant species was a lot more dramatic than I frankly had expected. Species like salmon berry it turns out are really well named. They tend to dominate in streams that have a large number of salmon and then they can out compete other species,said Mr. Reynolds.
The physical characteristics of a stream were a factor, because bears and other predators don’t like to fish in places where there are steep banks. Any angler who has tried to land a thrashing salmon while clambering up a slippery bank will understand why.
The researchers found plant species were different in areas where there were sloping banks.
If it is a small stream and has shallow banks, then there is a lot better chance that the plants will be effected by the carcasses, because these are more accessible to bears, said Mr. Reynolds.
The research team started the study in 2007, and by working in squads, were able to study one or two watersheds a day.
It was almost like having a SWAT team. We had a plant crew, we had a stream crew measuring physical characteristics, we had water chemistry work, looking at nutrients in the water. We would beach the boat each day and people would head off in teams of two and three and get to work. It was quite an effort., said Mr. Reynolds.
In the fall the team counted salmon in the streams, many which had never been enumerated before. They found runs that varied from barely a few fish, to more than 100,00. The run size information was then matched to a botanical census.
An earlier study, by Rachel Field and Mr. Reynolds, looked at the impact of salmon on bird populations around estuaries.
That research showed that the diversity and number of birds increased in relation to the size of the salmon run.
That paper concluded that breeding birds may benefit from residual salmon-derived nutrients in landscapes adjacent to spawning grounds and that this trend extends beyond stream riparian zones to estuarine riparian forests, and well beyond the salmon spawning season.
Mr. Reynolds was asked what is to be learned from these studies about the importance of salmon?
Well, smaller streams tend to get ignored by a lot of people. The department of Fisheries and Oceans . . . can’t count fish in every stream and they leave out the ones with smaller numbers of fish,said Mr. Reynolds. And yet these kinds of small streams are not exceptional. The types of streams we have been looking at are the norm along much of the [British Columbia] Central Coast. It’s not all Fraser and Skeena [Rivers] around here. These small streams do in aggregate produce a lot of salmon which are beneficial, clearly . . .and if we diminish the number of salmon returning to these systems we will be changing the vegetation and therefore other aspects of the stream sides.
Put another way, without the salmon, the nature of the forest will change – and the song birds will vanish.
Something to think about next time you release a fish.