Why do forests flourish on fish?


Ever since I went on my first expedition to the Canadian Arctic in 1958 I have kept a notebook, and this habit is still with me. Now, with this column on the first Thursday of each month, you too, Dear Reader, can share in these jottings from over the years.

It’s been 40 years since I first came to Japan, after my third Arctic expedition, and of my 62 years of life the longest sojourn by far has been spent in this country. Obviously, I like it here, though I do get tired of forever hearing how different everything in Japan is. For sure, its culture and history are unique, and this is an island nation. However, all of nature, and history too, is linked.

Take salmon, for example.

In prehistoric times most of the rivers of Europe, Asia and North America north of the 40th parallel provided salmon in great quantities to feed in the ocean waters and return inland. In their enormous migrations, Pacific salmon of North America intermingle with the salmon of Asia, all of them needing clean, unblocked, well-oxygenated rivers in which to live and breed — and die.

There are several species of salmon native to the northern Pacific from Alaska and America’s Northwest to Japan, Taiwan, the Korean Peninsula and Kamchatka in northeast Siberia. Among the best-known are the pink, chum, coho, sockeye and — biggest of them all — the Chinook, or king salmon, that can weigh in at up to 40 kg. Confusing things slightly are the Atlantic salmon that are found along the Pacific coast of Canada, where some escaped after being imported for fish farming in 1985.

Like salmon, there are also trout and char that go to the sea from their freshwater streams and return bigger and stronger and ready to reproduce. The most famous of these are the rainbow trout, which return as salmon-sized steelheads, much prized by anglers.

In Japan, sakura masu, satsuki masu and ame masu are well-known for their life cycles starting and ending in fresh water, with time spent in the ocean in between.

The take of once incredibly abundant wild salmon in Canada has dropped to a fiftieth of what it was. The reasons for this are many, and continue to be debated, but undoubtedly dams, pollution, overfishing and damage to their habitat by clear-cut logging and the resulting erosion are major culprits. Added to these are the effects of global warming on their marine habitats.

In Japan, the disgraceful treatment of rivers and their mountain tributaries is not something I want to go into on a fine clear morning, because the topic makes me start frothing at the mouth and snarling obscenities and terrible curses.

In contrast, across the Pacific in British Columbia and Oregon in particular, far-sighted people have been working hard to restore watershed habitat so that salmon, trout and char can once again resume their ancient life cycles. In April last year I attended an international conference in Eugene, Ore., convened to discuss these watershed issues and the restoring of nutrients to salmonid ecosystems.

One of the key speakers, Harv Forsgren, from the American Forest Service, put the issue very simply: “Fish need forests. Forests need fish. People need both.”

In Japan especially, we have long known that healthy mixed forests in the mountains help to create and maintain healthy streams, and these in turn are needed for healthy coastal fisheries. In other words, you need forested mountains for a reliable run of unpolluted fresh water carrying the nutrients and sediments that coastal fisheries thrive on.

However, it is now clear to scientists, as it has long been clear to native peoples, that the return of nutrients from the sea to the forests is also crucially important.

If you have ever seen a spawned-out salmon lying on its side in the shallows, body all battered and torn, gasping, waiting for the gulls and crows to peck out its eyes, then you have surely felt pity. However, the death of the spawned salmon is not a waste.

My friend Ken Ashley in British Columbia is one of the many who have been working and studying how to bring salmon back to streams ruined by flash floods and erosion. His research has made it clear that nutrients from dead salmon are crucial both to the survival rate of the young river-born fish before they go to sea, and to the homing instinct that later brings them back to breed and die.

Even if a stream is remade, its water pure and full of oxygen, with banks stabilized by bushes and trees, with pools and back eddies for young salmon, water deep enough below rapids so that migrating adults can gather momentum to leap, and with suitable deposits of well-washed gravel and reeds in which they can lay their eggs — even if all these parameters are met, the return rate of adults after being released as fry in a remade stream is still poor. Apparently to be lured back they needed the sacrifice of their parents’ lives.

Ken tried placing fish carcasses, gathered from salmon hatcheries along these streams, but it was hard, smelly, dangerous and costly work. I mean, would you like to backpack a load of dead fish through mountain country inhabited by bears?

So he and his associates developed a pellet containing the nutrients found in a salmon, but which could easily be carried and scattered by hand or by helicopter. They found that these extra nutrients enabled moss to grow on rocks, aquatic plankton and insects to flourish, and young fish to grow big and strong before leaving for the sea, from where — the scientists found — they would then return to breed in their turn. Once the cycle of returning salmon is restored, then all man has to do is to restrict his greed.

Another Canadian scientist at the Eugene conference, Tom Reimchen, an ecologist at the University of Victoria, had noticed how bears capture salmon at a stream then take them into the woods. They munch the back of the heads, rip the bellies open and devour the eggs, but will leave the male roe and about half of the fish before hurrying back to their fishing spot before another bear takes it. Tom estimated that a single bear would take 700 fish a year into the forest, of which about half the total body mass would be left to insects and other creatures. Did this have any effect on forest growth, he wondered.

He began to take cores from the trunks of trees in salmon-stream ecosystems and found that of the nutrients brought from the sea by the salmon — phosphorus, ammonium and many others — the heavy isotope of nitrogen, N15, could be identified in tree rings going back hundreds of years. You can count tree rings, and records have been kept of fisheries, fish canneries and logging activities for the last 100 years. Tom’s research over 15 years indicated that where salmon were returning from the sea, and nutrients from their bodies were being scattered in the forest by bears and other creatures, the trees were healthy — and growing more than twice as fast as otherwise. This also affected the success of other forest plants, promoting lush harvests of berries, which again attracted birds and bears, further enriching the soil and spreading seeds from their droppings.

Another vital function of the bears and other creatures was the removal of excess dead and decaying salmon from the water. Enough is nutrition and a homing beacon; too many and they cause oxygen-sapping pollution. Bears maintain the balance.

I was able to spend two weeks with Tom Reimchen and his assistants, filming his research and enjoying some of the most exciting and stimulating conversations of my life. We saw bears, wolves, otters, seals and whales, eagles, ravens, kingfishers. We also saw a stream around which almost all the bears had been killed, either by trophy hunters after grizzlies, or poachers taking black bears to supply the Asian market with their gall bladders and paws. That stream was choked with dead and dying salmon, stinking, with many dying before they could spawn. Later I’ll be writing more about these damned poachers.

Anyway, it is a clear truth. Forests do need fish, and if we really want to do something about it in Japan, where construction and pollution have killed salmon streams from Hokkaido to northern Kyushu, then we have to start seriously looking at senseless public spending and all its disastrous effects. I’ve thought about it, but I don’t think that the carcasses of certain politicians would favorably enhance river nutrients. Pity.