Indicator: Forest diseases

Why is this indicator important?

Forest pathogens play an important role in forest ecosystems as agents of tree disease. Although forest diseases contribute to the cycling of nutrients in the forest and can promote biodiversity by creating habitat, they can also cause significant economic loss in forests managed for timber production.

Dothistroma needle blight is an endemic forest disease in Canada. Recent increases in damage to lodgepole pines by the Dothistroma needle blight are believed to be linked to climate change.

What has changed and why?

Lodgepole pine affected by Dothistroma needle blight in central Alberta in 2015.

Lodgepole pine affected by Dothistroma needle blight in central Alberta in 2015.

Native trees and native forest pathogens have co-evolved for millennia, resulting in a fine balance in which native pathogen impacts on native trees are typically not catastrophic. However, this balance is threatened by climate change. For example, Canada’s boreal forest is expected to become drier as a result of climate change, and drought may contribute to increased damage from forest pathogens as defences of stressed trees are compromised. Forest pathogens also rely on suitable environmental conditions for spread and infection, which may be altered as a result of climate change.

In addition to climate change, the introduction of exotic pathogens, such as Cronartium ribicola (the causal agent of white pine blister rust), which continues to have a significant impact on Canada’s white pines, is a risk that also must be mitigated.

What is the outlook?

When combined, the impact of climate change and established and new invasive forest pathogens on Canada’s forests is difficult to predict and is potentially more serious than each issue on its own. Additionally, the geographic ranges of both hosts and pathogens are expected to change, as climatic suitability influences both host and pathogen, thereby facilitating change in the range of pathogens. Forest managers must plan for increasing impacts from forest pathogens as part of their climate change adaptation strategies.