The willows are weeping, the aspen are trembling and the poplars are pleading, but no matter; the subalpine fir has been formally designated as the Yukon's official tree.

In a contest held by the territorial government in 2001, almost one-third of the votes were for the fir, beating out the other three choices of flatleaf willow, trembling aspen and balsam poplar. Most of the voters were school kids, and some adult eyebrows have been raised over the fact that the Yukon's official tree is not particularly abundant in the territory's forests today.

But at least one person thinks the voters were on the right track. "I think they made a good choice. Subalpine fir might not be as important of a tree now, but it certainly was in the past," says Charles Schweger, a paleo-ecologist at the University of Alberta.

Also, he thinks that subalpine fir are no longer as abundant or as widespread as they once were because humans have been modifying the landscape ever since they arrived on the scene, starting fires that favour some trees over others.

Schweger has studied everything from lake sediments to fossil pollen to try and determine what the Yukon looked like in the distant past, particularly in the periods called interglacials which occurred between the different ice ages. Over the last few million years, glaciers have covered what we know today as the Yukon at least 20 times.

Schweger says he has not been able to determine exactly when subalpine fir first showed up in the Yukon following the last ice retreat, but aspen and birch probably arrived first, followed by spruce. Lodgepole pine arrived more recently, appearing just a little more than a thousand years ago.

But subalpine fir has definitely been here for more than a little while. Fossil pollen proves that 200,000 years ago, subalpine fir grew as far north as Old Crow and was also more abundant than it is today. Today these trees are usually found growing at higher elevations, typically near treeline, but in the past they grew at lower elevations in areas where lodgepole pine are abundant today.

Today lodgepole pine is abundant in many of the interior forests, and Schweger thinks that fires have brought about this change. Lightning would have sparked some of the blazes, but he thinks that humans probably caused their share of them as well, helping to make our present interglacial different from all of the ones that came before it.

"I have been arguing that our present interglacial is unique. If you look at what is ecologically different, there are two things that stand out. There are no big Pleistocene mammals like mastodons and mammoths, and there are humans. And what do humans do with forests, they burn them."

People used fires more on an everyday basis, for cooking, signaling and keeping insects at bay. While it is not known whether or how often fires were deliberately set, Schweger says it is likely that people had a different attitude about fires back then.

"They did not have the European ethic that you had to protect the forest from fire," he says.

Subalpine fir do not come back readily after fires as their cones and the seeds within are also destroyed. But fires favour species like lodgepole pine as their cones are sealed shut with resins. It takes the heat of a fire to melt the resins so that the cones open and the seeds are scattered.

Schweger says that if his theory is true, that means that humans have shaped the boreal forest we see today.

"In North America we have always assumed that our natural landscapes are wild and do not have much of an imprint from human activities. But if we accept that humans are responsible for burning and that is why we have more lodgepole pine than fir in the forests today, that means that the Yukon forests are cultural landscapes."

Professor Schweger can be contacted at (780) 492-3489 or by e-mail at charles.schweger@ualberta.ca.