SpruceRoots Magazine - September/October 2000

 

 

Part of the fragmented landscape on the Skidegate Plateau

TFL 39, Block 6.

 

 

 

Streams of Conscious

by Erica Thompson

How many islands make up Haida Gwaii? Two answers come to mind. The first, constructed from a string of measurements -138 islands in the archipelago, 42 fresh water lakes, over 1,600 kilometres of shoreline, and mountain peaks surpassing 1,000 meters above the surrounding sea level, all embodied 100 kilometres from BC's northern coastline ...

The second, moves within these surveyed landscapes, defining 'islands' in terms of biodiversity, continuance and extinction.The way animals and plants are distributed over the earth is the business of biogeography. Why certain species are found in one place and not another, how they arrived there and what happened to the ones before them, is bound in worldviews and methods from biology, chemistry, paleontology and geology with roots going back to evolutionists Charles Darwin and Alfred Wallace. More relevant to Haida Gwaii is 'island biogeography' - a theoretical window into the stories of plant and animal, living and disappeared, from an island's sky, land and sea. How and when they came to be here, and the pressures on their continuance, are the affairs of what has come to be known as 'the theory.'

In 1967, E.O. Wilson and Robert MacArthur's 'island biogeography' turned the study of ecology on its head. They examined islands denuded by volcanic activity and documented the floral and faunal patterns of colonization upon these rocky outcroppings. In time, the two young ecologists came to view islands as dynamic communities where resident populations were the result of episodic immigrations and local extinctions. They developed a series of concepts to mathematically predict the number of species they could expect to find residing on an island once the immigration and local extinction of species levelled out or as they called it "reached equilibrium." Their variables included isolation - the number of species on an island is related to distance. The further away an island is from the mainland, the less species one can expect to find there due to fewer incoming species and continued rates of extinctions, and secondly, the size of the island. In general, smaller islands have fewer species than larger islands and suffer more extinctions. The ecologists did not specifically address which species would succeed and which would fall away; their efforts focused more on 'species turnover' - new species immigrating to the island displacing the local ones.

On Haida Gwaii, island biogeography and the uniqueness of island species has long captivated the interests of many scientists. According to J. Bristol Foster in Islands At the Edge, Haida Gwaii's remoteness from the mainland and the lack of glaciation on parts of the island have contributed to the island's outstanding ecological makeup. There is a strong likelihood Haida Gwaii has exceptionally old life forms, and in some cases not just newcomers since glaciation.

"We do not know for sure which of the plants and animals now found on the Charlottes arrived first. We do know, however, that most unique forms of the native land mammals (deer mouse, black bear, pine marten, ermine, dusky shrew, caribou), the saw-whet owl, Stellar's jay and hairy woodpecker, certain insects, amphipods, stickleback fish, mosses, liverworts, and several flowering plants live only on the Charlottes and nowhere else in the world," wrote Foster.

In accordance with 'island biogeography,' he noted, "islands always have fewer species than the nearby mainland. The Charlottes has the Stellar's jay, saw-whet owl, hairy woodpecker, blue grouse, screech owl, downy woodpecker, ruffed grouse and evening grosbeak present on the adjacent mainland. There are native black bears but no grizzly, marten but no fisher, deer mice but no voles, chipmunks or native squirrels. There are ermine on the islands but no least weasels. There were caribou but no native deer, goats or sheep."

In addition to fewer species, there are fewer predators and competitors once a species does reach the island. "This fact," Foster said, "can alter the whole basis for their survival. The selective forces are different, as will be the animals themselves after enough generations."

Like Wilson and MacArthur, Foster said the more isolated and smaller the island the fewer the number of species that will be present. "Within the Charlottes, black bear, marten and ermine are not found on the smaller islands," he stated.

Lastly, Foster identified the local extinction of island species by immigrating mainland forms saying "this is because mainland forms tend to be more efficient than relatives on islands," he said and also as a result the roster of species turns over. The disruption of natural systems through the introduction of deer, and their impacts on young cedar, and rats, with the resulting decimation of seabird colonies, provide ample evidence of the impacts introduced species have on island ecology.

Islands Within Islands
More than 30 years since MacArthur and Wilson first presented their ideas on islands as models for predicting rates of colonization and extinction among isolated landscapes, rigorous debate over the applicability of the theory to other geographic areas has waged in the pages of academic journals. Today the notion of equilibrium or a balance between immigration and local extinction has been overshot in many parts of the world by the widespread crisis of endangerment and extinction. In addition, the very notion of what constitutes an 'island' has evolved to include landscapes found miles from any body of water. 'Virtual islands' or patches of habitat are the islolate spaces between cities, agricultural fields, and the bewildering clearcuts where forests once stood. These pockets of habitat are remnants that can look good but may or may not be viable for the plants and animals marooned with their borders.

Says David Quammen from Song of the Dodo, "It's one thing to mark off an isolate of some ecosystem and call it protected. Whether the species and relationships within that isolate persist over time, after the landscape all around it has been trashed, is another thing."

The Fragmented Landscape
The islands of Hadia Gwaii have a head start when it comes to fragmented habitat. Geographer, Marguerite Forest, says Graham Island is already naturally fragmented to a significant extent as Masset Inlet and the Queen Charlotte Mountain range divide it in a northeast and southwest direction.

"Each half is even more fragmented by swamps in the east and mountains in the west. This means that naturally there is very little interior lowland forest. The only significant link between east and west is in the lower Yakoun valley," she says, and it is precisely here in the Yakoun where the heaviest imprints of human-made fragmentation occur in the form of logging and road building.

The implications of fragmentation are species and site specific. For example, Forest says, "a lot of the comparisons depend on the species of animals or birds that are of concern. Some small creatures like salamanders can't even get across a logging road, let alone a large clearcut. Some birds like murrelets depend on old growth for nest sites, so cutting down the forest is like having whole islands disappear ... Other species like bears don't do too badly, because they are much more mobile over longer distances and because they are generalists that survive in a wide range of habitats."

As marbled murrelets depend upon old growth nest sites, Forest says, bears need large hollow denning trees for survival, and reductions in such critical habitat has reproductive repercussions throughout the bear population. "With small, genetically speaking, populations on Haida Gwaii this might be a problem in the long run in terms of genetic diversity and inbreeding," she says. Some important sites, like large hollow denning trees may not be available, and that might affect how well the population reproduces.

Across the Landscape
There are people working to address the issue of virtual islands and fragmented landscapes. One process familiar to Haida Gwaii, is ecosystem-based planning - an approach based primarily on the sciences of landscape ecology, conservation biology, forest ecology, hydrology, and ecological economics.

"We have developed ecosystem-based planning to maintain the ecological integrity of islands and archipelagos, like Haida Gwaii. In that sense, [ecosystem-based planning] is based on island biogeography," says Forest Ecologist, Herb Hammond.

Ecosystem-based planning works to maintain ecological integrity through maintaining landscape linkages and corridors, riparian area health, and by identifying and protecting habitat nodes across the landscape. Planning requires a close up look at landscapes to understand the characteristics and conditions at work. The characteristics describe how the ecosystem functions and provides the basis to determine essential make up and the structures which will best protect and maintain ecosystem functioning, says Hammond.

"A key concept here is that connectivity must be protected at all spatial scales from large 'cross-island linkages' to the connectivity provided by ephemeral streams. Protecting ecosystems means developing a plan which represents the full spectrum found on island, connected in a pattern that adjoins the linkage/corridors, riparian ecosystems, inter-tidal zone and adjacent terrestrial ecosystems," he says.

According to Hammond an effective plan must include large reserves like the Tlell watershed, in order to maintain species and healthy genetic pools, and large enough to withstand natural disturbances like fire and wind.

"For example, the Tlell watershed, not only is virtually the last opportunity for a large reserve on the east coast of Graham Island, but also, it is the last nearly unfragmented corridor (east-west) across Graham Island," states Hammond.

Outside and Up in the Air
It is only a short drive out of town, any town on the islands, to the forest's edge and it is here amongst the trees, creeks, rock and soil where island stories dwell. It is also here, in the forest, you realize island biogeography is not merely the stuff of mathematical models and theories, it is a glimpse into the earthly history and the future of the most distinctive of homes.

If you fly above the Islands and look down, you can see the forests as patterned as a patchwork quilt. From the air, the concepts that are island biogeography, are revealed in startling simplicity through the black and white of how much has been taken and how little remains. And here, miles above the ground, the relationships between biodiversity, continuance and extinction seem exceptionally clear. For an aerial glimpse of this concept go to http://www.spruceroots.org/Gallery/Logging.html

 

Notes:
Quammen, David / Song of the Dodo ­ Island Biogeography in an Age of Extinctions. Scribner: New York. 1996.

Islands Protection Society. Dr. J. Bristol Foster. Islands at the Edge. Douglas & McIntyre: Vancouver. 1984.


SpruceRoots Magazine - September/October 2000