Of all the threats to boreal biodiversity, the loss and conversion of ecosystems are probably the most significant. Animals that are peculiar to one ecosystem, their habitat, will quickly leave their location once this has been destroyed, and probably begin searching for another location, one that human beings have been kind enough to spare them, generally fragments of little size.

What happens to these new homeless? Investigation, particularly in the Lac-Saint-Jean area, has shown that game species can enlarge their territory in order to compensate for land loss, but we do not know much about the longer-term consequences on their lifestyle. We may also wonder what will happen to future generations of animals in these fragmented habitats. Very often, these pockets of habitation will lose their wildlife potential and the wildlife population itself will decline within these residual habitats.

In what way will the potential of these fragmented habitats diminish? First, for certain species, even migrants, the fragmented habitats are so remote that they raise problems of access. For example, the Palm Warbler (Seiurus aurocapillus), a small woodland bird, comes back every springtime from its annual migration to the Tropics and it needs to find a territory in the Borealie. Once it returns to this territory, it will stay there all summer. As an experiment, we captured and removed dozens of these birds to a spot four kilometres away from their territory in order to determine their potential for mobility. The Warblers found it more difficult to go back if they had to cross unwooded zones rather than unbroken forest, suggesting that the fragmentation of the woodlands does effectively impact negatively on their movements.

Another problem characteristic of fragmented habitats is the edge effect, which is more serious when remaining habitats are small in size. Indeed, the area surrounding the habitats is often contaminated by external elements, such as the presence of new predators or negative changes in the micro-climate, and it is to these factors that we attribute the frequent desertion of small clusters of habitats by wildlife. Fortunately for the boreal ecosystems, the edge effect seems more frequent in the south, on agricultural land. Finally, the fragmentation of habitats may lead to social dysfunction amongst the animals, because they often need to cohabit with a number of their own kind in order to improve their chances of reproduction, and this often requires unbroken areas of habitat greater than what remains to them after human beings have passed through.

Although we do have a growing number of examples of the above phenomena, a great deal of work remains to be done before we are fully able to understand the impact of habitat fragmentation and predict its consequences in a more detailed fashion.

Dr André DesrochersProfesseur agrégé                                                               
    
Département des Sciences du Bois et de la Forêt
Université Laval

mai 2003