Northern exposure: can the planet-encircling boreal forest survive global warming and resource exploitation?

Natural History, Feb, 2005 by J. David Henry

It's a clear autumn morning in northern Saskatchewan, and I am knee-deep in a peat bog. An invigorating breeze sets lemon-gold aspen leaves quivering in the surrounding hills, while above me, steeple-topped spruce trees sway in unison like a Baptist church choir. I bend forward, stretch out my fingers, am bury them deeply in the purple cushion of sphagnum moss. As my fingers sense the icy cold, I feel rooted in all the wetlands of the taiga--the boreal, or northern forest that encircles the globe from Siberia to Scandinavia, from Newfoundland to the interior of Alaska. Viewed from outer space, the taiga appears as a dart green mantle draped across the shoulders of the Earth. At ground level it comprises tracts of both dense and open-canopy forest dominated by conifers such as fir, larch, pine, and spruce, interleaved with boggy terrains. In Eurasia as well as in North America, the habitat extends some 4,000 miles east to west, and anywhere between 600 and 2,000 miles north to south, for a global total of some 1.5 million square miles [see map on preceding page]. The coniferous forests of the taiga make up 27 percent of the world's forests. Nothing like this vast, circumpolar ecosystem occurs in the Southern Hemisphere. At comparable southern latitudes--between fifty and seventy degrees--there is little land and much open ocean; moreover, conifers in the Southern Hemisphere are usually confined to higher elevations.

In North America at least, the northern and southern limits of the boreal forest are determined by the boundary between the frigid Arctic air overlying the Far North and the warmer air overlying the continental interior. The boundary between these air masses shifts with the seasons: its average winter position determines the southern limits of the boreal forest; its average summer position determines the northern limits. Trees and shrubs that fall within the winter range of the Arctic air mass must be able to survive minus-40-degree (or colder) weather for a month or longer. Only such hardy species as aspen, black and white spruce, Labrador tea, and tamarack can withstand such conditions--which they do by actively transporting water out of their living cells at the start of winter. As summer approaches, the air-mass boundary shifts northward, but north of it conditions remain too cold for the forest vegetation to prosper. The habitat gives way to the Arctic tundra, a treeless zone dominated by grasses, lichens, and sedges.

What alarms those of us who study the ecology of this vast northern habitat is that it is under siege from two great threats. One is global warming. The average annual temperature of the Earth's surface has risen by 9 degrees Fahrenheit since the end of the last ice age. Most climatologists agree that one degree of that increase--more than 10 percent of the total--has taken place in the past hundred years alone. And the Arctic is warming nearly twice as fast as the rest of the planet.

Studies of past variations in climate show that the boreal forest is sensitive to even small trends in temperature change, though how the forest will respond to global warming is hard to predict. For example, one might assume that the warming will drive the tree line northward and into higher elevations. But Isabelle Gamache and Serge Payette, both biologists at the University of Laval in Quebec, found that though black spruce forests near the tree line in northern Quebec have undergone accelerated growth in the past decade, they have seldom produced a good crop of cones. Hence the tree line in this region has not yet moved beyond its historical northern boundary.

The second great threat to the taiga is exploitation by people. In many areas around the globe, timber from the taiga is being harvested at unsustainable rates, and clear-cuts and logging roads have made the forest into a patchwork quilt. Cut lines pierce the habitat so that the underlying rock strata can be probed seismically for oil and gas, and pipelines are built to carry the fossil fuel. Massive hydropower developments are flooding large areas, disrupting caribou migration routes and allowing silt to accumulate in gravel spawning beds, making them unsuitable for the fish.

There is also a third, nonphysical threat to the habitat. It may be the biggest threat of all: many people just don't care. In North America the taiga is often devalued as "the land of little sticks," "just the bush," or "the land that God gave Cain." To many the habitat is nearly worthless, with poor soils that are difficult to farm and stunted trees good only for making grocery bags, newsprint, and toilet paper. Whatever resources there may be--or so goes the prevailing attitude--should be freely exploited. Many people from Siberia and western Russia, and, to a lesser extent, from Finland and Scandinavia, hold similar views.

Global warming and resource exploitation pose a one-two punch to an ecosystem that has flourished since the continental ice sheets melted away: the taiga has occupied its more southerly regions for between 10,000 and 12,000 years, and more northerly reaches for between 5,000 and 10,000 years. But just what do we stand to lose in this "land of little sticks"? And what, within human means, can be done to preserve it?