Although more in carbon dioxide in the atmosphere may encourage tree growth, the negative impacts of climate change are expected to far outweigh any benefits.

Forest dispersion and shifting

Canada forests are expected to be among the most vulnerable in the world to climate change because temperatures are expected to increase more in the arctic, bringing with it changes in precipitation. Although scientists do predict an increase in precipitation, it will likely not be sufficient to keep up to increased evaporation for rising summer temperatures – leading to decreased soil moisture. This will cause more drought-resistant trees or grasslands to replace existing forest ecosystems.

* During the last 50 years, summer temperatures frequently exceeded the critical threshold of the most valuable timber species of the North American boreal forest, the white spruce. Over the coming decades, scientists predict continued hot summer temperatures associated with climate change would force this species into sharp decline, potentially to extinction.

Rising treelines

The alpine treeline is one of the most distinctive habitat transitions, separating continuous subalpine forest from the alpine environment.

Treeline elevation is determined by growing season temperature. As global temperatures rise, treelines are expected to advance upslope, shrinking the alpine environment (e.g. invading alpine meadows) and fragmenting wildlife habitat. Climatologists believe that a rise in global temperatures of 3.25 degrees Celsius would be equivalent to an ecological shift upwards of about 500 metres in altitude. Alpine species confined to the tops of low-lying mountains risk extinction as the habitat is taken over by forests.

Example:

Extensive upslope migration of treeline has been documented in areas of Jasper National Park during the last century.

Forest fires

Hotter, drier summers are expected to increase evaporation and generally worsen the severity of fire seasons and increase the risk of forest fires across most of Canada.

* According to the government of Canada, both fire frequency in Canada’s boreal forest and total area burned have increased over the last 20 to 40 years.

Forest disease and pest infestations

Warmer temperatures are also expected to expand the ranges and enhance the survival rates of forest pests such as the spruce budworm and the mountain pine beetle.

* Infestations of the mountain pine beetle are normally controlled by intense cold snaps in the winter, but warmer winters have been one of the factors enabling the infestation to grow into an epidemic in British Columbia’s interior forests. Over the next 10 years 80 per cent of B.C.’s mature pine forest is expected to be lost due to the infestation of the mountain pine beetle.

Links: http://adaptation.nrcan.gc.ca/perspective/summary-06_e.asp http://adaptation.nrcan.gc.ca/perspective/forest-01_e.asp