Population dynamics in boreal forests

Ilkka Hanski

Metapopulation Research Group, Department of Ecology and Systematics
University of Helsinki

This presentation addresses some key issues in the dynamics and persistence of species in the boreal forests in Finland and elsewhere in northern Europe. All of northern Europe was glaciated, and hence the species that we have here today have migrated from elsewhere during the past 10,000 years. Some specialist species, such as the beetle Phyto kolwensis, may have arrived from far-a-way glacial refugia and lost much of their genetic diversity in this process. These species may have limited capacity to respond to environmental changes such as climate change.

Today, human-caused loss and fragmentation of virgin forests poses a serious threat to the survival of at least 1000 species. Many old-growth forest specialist species have limited dispersal capacity, which makes them especially vulnerable to fragmentation. Communities of specialist species in small fragments of old-growth forest may show cascades of population extinction, as exemplified by a study of an insect community inhabiting the bracket fungus Fomitopsis rosea. Fragmentation is however a complex process, involving both a temporal as well as a spatial component.

Mathematical models have been developed to assess the population dynamic consequences of spatio-temporal fragmentation. In southern Finland, there is so little virgin forest left that the only way to prevent hundreds of species from going extinct is to initiate an extensive program of restoration of natural-like forests. Several different options are available, and their relative merits can be assessed with mathematical models.