Has the web of life been broken, beyond any hope of repair?
by Maggie Paquet ©
Back in autumn 1999, newspapers and at least one national magazine carried an article by Tom Reimchen of the University of Victoria Biology Department on the links between bears, salmon, and forests in the coastal ecosystems of British Columbia.
These were exciting articles for people interested in the workings of ecosystems. While some of us were aware the nutrients of salmon carcasses enriched the narrow confines of what the Forest Service deems to be riparian zones just because of their proximity to rivers and streams, Reimchen's research shows that the influence of the mighty salmon reaches much farther into the forest than previously thought, and brings with it basic nutrients from the far reaches of the Pacific Ocean. And the principal conduit for this expanded influence is none other than that oft-misunderstood omnivore: the bear.
"I proposed to determine who were the major foragers on salmon during the autumn migration and to determine how important salmon were to these foragers. If salmon were only an incidental food for these species, then yearly fluctuations or reductions in numbers of salmon returning to rivers would have little impact on local biodiversity.
"In contrast, if salmon were a major food, then the decline of salmon from habitat loss or over-harvest in the commercial fisheries would have a large impact," said Reimchen.
Reimchen's initial interest was in the foraging behaviour of bears, but, as frequently happens when scientists get into the field, their research can take fascinating and serendipitous turns. While bears are truly interesting creatures, their importance within ecosystems is at best poorly understood. When I was writing the background document for the BC Grizzly Bear Conservation Strategy, I asked numerous people, both in and out of government agencies, about the roles of bears in natural systems. The general consensus was that bears, while important intrinsically, were "probably" not really critical to the functioning of any given ecosystem. Sure, they may rip open a few logs and tear up some alpine slopes, even be major predators in a few systems, such as the Spatsizi, but if they weren't there, those functions would "probably" be taken up by other organisms.
Reimchen showed that bears–both black bears and grizzlies–are major foragers of (mostly) spawned-out salmon. They carry the salmon carcasses deep into the forests, eat the preferred portions, and abandon the remains for other species to scavenge: gulls, crows, ravens, eagles, marten, numerous insects including ground beetles and fly larvae. As well, forest plants, such as huckleberries and devil's club, take up the nutrients from both the rotting carcasses and the scat from bears and other animals.
Bear Management A "Disaster" Thirteen dead grizzlies in Oweekeno Village on BC's mid-coast should alert the public that government's bear management policies are a disaster for bears in the province, says the Valhalla Wilderness Society. "The Rivers Inlet-Oweekeno was once one of the most productive grizzly areas on the BC Coast," says bear biologist Wayne McCrory, a former member of the BC government's Grizzly bear Scientific Advisory Committee. "Now it's undergoing ecosystem collapse. Over-hunting, excessive logging, and a drastic loss of the salmon are responsible." BC has become known as the bear-kill capital of the world. In Washington State, with a much larger human population than BC and despite a high black bear population, only about 60 bears were relocated or destroyed in 1998, compared to BC's huge slaughter of 1,619 black bears and 35 grizzlies. * Valhalla Wilderness Society, New Denver, BC V0G 1S0; ph: (250)358-2333; fax: (250)358-7950; email: vws@vws.org; website: http://www.savespiritbear.org |
Tracing the nitrogen
The means for tracing this interconnectedness is N15, the heavy isotope of nitrogen. Scientists know that N15 occurs at higher concentrations in the ocean than in the atmosphere, so N15 is a marker for nitrogen from the ocean. N15 increases with each higher trophic level and salmon, on the fourth trophic level, have elevated levels of N15.
Reimchen says, "One of our most interesting findings over the last eight years of this research program suggests that the annual return of salmon into BC's coastal rivers provides the largest single pulse of nitrogen-rich fertiliser for the forests around salmon rivers. This relationship is established by identifying trace signatures of the nitrogen isotope N15 in the growth rings of ancient trees … Based on isotope ratios, approximately 13% of the nitrogen found in fresh plant tissues comes from salmon nutrients. Salmon-derived nitrogen is also incorporated into the wood of trees and, in some of the ancient giant trees, up to 50 percent of the nitrogen–this essential nutrient–has come from salmon."
Most gardeners know about the importance of nitrogen; it's one of the principal components of all kinds of fertilisers and is an essential building block for all living things.
Atmospheric nitrogen is converted to inorganic nitrogen in soils for use by plants by a process called nitrogen fixation. This process is carried out by soil bacteria, blue-green algae, and certain symbiotic micro-organisms in association with legumes. Plants take up nitrogen and convert it into organic compounds, chiefly amino acids and proteins, which are assimilated into the bodies of plants and animals, which then excrete the nitrogen (or offer it through their decaying bodies) back to the soil. And so the cycle continues. The fact that inland plants and animals contain nitrogen from the ocean is more than an interesting factoid.
Reimchen's research is important in our efforts to learn more about how forest ecosystems function. Coastal forest diversity and biomass are extremely high. In watersheds where there are salmon, there is a much higher diversity of species; insects, amphibians, birds, mammals, plants-everything-than in watersheds with no salmon. Reimchen believes the presence of salmon can be a major predictor of the other species in a given ecosystem. Who can say how much of this increased biodiversity is dependent on the N15 isotope or on how it gets to be distributed within the ecosystem?
The research certainly shows that the salmon is a keystone species.
A keystone species is one that affects the survival and abundance of many other species in the community in which it lives. Its removal or addition results in a relatively significant shift in the composition of the community and sometimes even in the physical structure of the environment.
In one location, Reimchen estimated that 2,500 kg of nutrients from salmon carcasses were converted to dipteran (fly) larvae. Songbirds consume huge amounts of these insects. If salmon disappear from a watershed, will the riparian songbird community be compromised because of the lower numbers of insects available as food for them?
His research also points to the fact that there are keystone elements to the ecology of bears, a hitherto unappreciated factor about ursus species throughout BC. So far, Reimchen believes that as salmon are depleted, so too will be the biodiversity throughout forest ecosystems in BC.
What happens to the bears when the salmon are gone? What happens to forest biodiversity when the bears are gone?
What Tom Reimchen has done is expose yet another thread in the marvellous complexity of interactions within living systems. Unfortunately, we seem to be bent on unravelling the web of life, even though our knowledge and understanding of how such a marvel is woven is still far beyond our skein of knowledge.
"Polar bears range throughout the arctic wherever there is pack ice … The most comprehensive studies of polar bears have taken place near Churchill, Manitoba, in the newly created Wapusk National Park … With the return of ice in the fall, hungry bears immediately move out onto Hudson's Bay to begin the season of hunting. Any decrease in the abundance of seal prey, or in the length of time the ocean is covered with ice, can be expected to have devastating effects on this … population. Again, although causation remains to be established, expectations and observations are matching up. As predicted under scenarios of the effects of global warming, birthrates have declined and the average physical condition of adult bears appears to be worsening. Wapusk is outstanding [also] because of the diversity and abundance of its … bird communities. An estimated 15% of all of the world's species breed in the arctic … by altering the planet's atmosphere, we are creating a huge experiment that appears likely to play out at the expense of these arctic organisms."
* Climate Change: Parks at Risk: Report: North America: AK/Arctic: Wapusk National Park and Central Arctic Bird Sanctuaries, World Wildlife Fund; www.panda.org/climate/parks/dr_na_park5.htm
"The boreal forest of North America is the largest block of more or less intact forest remaining in the world and is rivalled in area only by the boreal forest of Russia and the tropical rainforest of the Amazon … Within this immense area, diverse ecological conditions are represented … the vast and pristine nature of parts of the boreal forest does little to protect it from the invisible reach of atmospheric pollution. Climate models consistently predict widespread ecosystem change under greenhouse warming, with damaging results. Already, these impacts appear to be under way. A pattern of consistent warming in the last 140 years has seen melting of the sparsely distributed and discontinuous permafrost characteristic of the boreal and taiga forests … Models suggest that the warming will lead to lowering of local water tables and…reductions in … wet lands. Equally seriously, large-scale disturbances such as fire and insect outbreaks … are predicted to increase in frequency … Perhaps most seriously, studies predict a decrease in forest productivity in the region … The predicted increase in forest fires and eventual transition to a landscape of young regenerating forest, is of particular concern for wildlife species that make extensive use of mature and old-growth forests, such as marten, fisher, and caribou … The possibility of large-scale forest die backs is made more alarming by the possibility that they may occur very rapidly."
* Climate Change: Parks at Risk: Report: North America: AK/Arctic: Wapusk National Park and Central Arctic Bird Sanctuaries, World Wildlife Fund; www.panda.org/climate/parks/dr_na_park5.htm
First the ecosystem, then the economy
The availability of research evidence of ecosystem damage, if not outright collapse, is vast. Once the ecosystems start to go, can the world's economy be far behind? What critical mass does awareness have to reach before the paradigm shift occurs?
What are the links between economy, ecology, ecosystems?
The word economy comes from Greek oikos (house), and nomos (manage); so "economy" means, managing the house. Since Earth is our house, economy means an activity to manage Earth, and not specifically money, as practically everyone, it would seem, thinks it means. Political economy is "the theory of production and distribution of wealth." The word ecology also comes from oikos (house), and logy (branch of knowledge); or knowledge about our house-Earth. Most of us are by now familiar with the word, but it has only been in use for about 100 years.
One of the most basic primers on ecology explains it as:
"The organized body of knowledge that deals with the interrelationships between living organisms and their environment …"
* Basic Ecology, Buchsbaum, Ralph and Mildred, 1957; The Boxwood Press, Pacific Grove, CA.
Knowledge becomes natural history
The authors acknowledge that "the observation of plants and animals in their natural 'homes' has been going on during all the million or more years that humans have sought them as food, for clothing, or avoided as enemies." The steady accumulation of all this observation and knowledge developed into a systematic collection of facts we now call "natural history." Unlike other sciences, which became highly systematised early in western culture, ecology, "as a body of principles, lagged behind … necessarily so because of its complexity and comprehensiveness. Including within its theoretical scope all physical and all biological phenomena, ecology has had to await the development of many other sciences before it could advance much beyond the descriptive stage." The more we learn about ecology, the more aware we become of just how difficult it is to manage this house called Earth. In fact, so far, there is very little evidence that we can manage it. Certainly research like Tom Reimchen's helps in our quest for understanding our home.
The Canadian Oxford defines ecosystem as, "a biological community of interacting organisms and their physical environment." This definition gives no real hint of the complexities of interactions not only between the living organisms, but between the biotic and abiotic factors; nor does it inform us of the entire range of complexity from the micro- to the macro-ecosystem scales.
And how does the concept of "ecosystem" relate to ecology and economics? The popular understanding of the word ecosystem generally focuses on living organisms. One person says, for him, it means "the great web of life." Society is slowly accepting the realisation that the state of our global and local economy is dependent upon biodiversity and the health of ecosystems.
Economies are tied to ecosystems
Here are some additional quotes from my research:
"The management of biodiversity is an issue that affects the quality of life of all Canadians. Human societies and regional economies are tied to resources produced by ecosystems. The impacts of change in ecosystems are expressed through shifts in biodiversity. Shifts in biodiversity alter the resource base of regional economies, often to the detriment of human populations … one of the most revealing indicators of sustainable management of biodiversity resources in Canada is the number of species listed at risk: 256 in 1996."
* EMAN'S Contribution to the Implementation of the Canadian Biodiversity Strategy; Ecological Monitoring and Assessment Network (EMAN); Environment Canada, 1997.
Consequences become more clear
"The trends of environmental deterioration of the last few decades cannot continue indefinitely without eventually affecting the world economy. Until now, most of the economic effects of environmental damage have been local: the collapse of a fishery here or there from over fishing … or the abandonment of crop land because of soil erosion. But as the scale of environmental damage expands, it threatens to affect the global economy as well."
"The consequences of environmental degradation are becoming more clear. We cannot continue to deforest the earth without experiencing more rainfall runoff, accelerated soil erosion, and more destructive flooding. If we continue to discharge excessive amounts of carbon into the atmosphere, we will eventually face economically disruptive climate change. If we continue to over pump the earth's aquifers, we will one day face acute water scarcity. If we continue to over fish, still more fisheries will collapse. If over grazing continues, so, too, will the conversion of range land into desert."
* The Agricultural Link: How Environmental Deterioration Could Disrupt Economic Progress; Brown, Lester R.; Worldwatch Paper 13, 1997; Worldwatch Institute, Washington, DC.
Moving on down the food chain
A recent study in the journal Science by Daniel Pauly and Johanne Dalsgaard reports that humans are systematically reducing fish catches by removing the commercially valuable fish species first and then moving down to the next valuable species and then the next and the next. "The product of this type of fishing is a reduction in ecosystem value … Given our current fishing practices we could end up eating plankton and seaweed in 30 to 40 years."
To which I can only add: Amen. The prospect of dining on plankton and seaweed ought to be sufficient impetus for shifting the current paradigm of unsustainable resource use.
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[From WS February/March 2000]