A Crisis in Subalpine Forest Health
Editor's note: Are our subalpine forests in crisis? And what would that mean for western Canada's alpine environments? The ACC is committed to conservation of mountain environments, including encouraging research and promoting findings.
This article by Philip J. Burton (Ph.D., R.P.Bio., University of Northern British Columbia, Terrace, British Columbia) and Vernon S. Peters (Ph.D., The King’s University, Edmonton, Alberta) explores the man-made and natural threats to these unique forests and their inhabitants and shares some of the scientific research that is driving a recovery plan.
This article will appear in the ACC's upcoming State of the Mountains Report 2018, which will be published in May. We'll continue to publish more articles exploring the science of the current state of Canada's alpine on our blog throughout the year. Find them all here.
The shoulders of western Canada’s magnificent mountain ranges are wrapped in a shawl of natural and wild forests. These forests are dominated by Engelmann spruce and subalpine fir in the Rocky Mountains and other interior ranges, with the addition of mountain hemlock and Pacific silver fir in coastal mountains.
Although appearing uniform and ageless from a distance, there is considerable diversity and ongoing dynamics in high-elevation forests. The ecotone (ecosystem boundary or interface) marking the transition to treeless higher elevations is typically a complex mosaic of meadows and tree islands rather than a discrete “tree line” following an elevational contour. Trees may advance or recede, depending on favourable weather conditions and seed production.
The native balsam bark beetle often kills subalpine fir trees individually or in small clusters, creating gaps that facilitate the release of smaller trees and the overall maintenance of old-growth forest. Lodgepole pine often dominates after fire, though rarely extends to or persists at tree line. Other less common species such as alpine larch add diversity and seasonal color that draws visitors to locations such as B.C.’s Cathedral Provincial Park. Lesser known yet critical “wildlife” tree species are also found at high elevations, including whitebark pine and limber pine, which can take on bonsai-like growth forms where they persist on dry windswept edges.
species at risk: Whitebark and Limber Pine
It is the fate of those latter two species, whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis), that is of great concern to forest ecologists in western Canada today. These two subalpine species are suffering from the onslaught of an invasive fungal pathogen known as white pine blister rust. Originating in central Asia where native pines developed resistance to its pathological effects, the rust was imported from Europe to North America on contaminated nursery stock over a century ago, and continues to expand its range in the western half of the continent.
Forest decline varies greatly regionally and between the pine species. Infection and mortality levels are generally higher in southern portions of their Canadian range, but are increasing more rapidly in northern regions. Infection occurs when fungal spores penetrate the needles, and grow filamentous stands that deplete plant sugars while spreading to the trunk. The presence of bark lesions (“blisters” similar to the ones shown on the image above) on the trunk signals another tree will die a lingering death over several decades. Simultaneously, infected trees disperse spores to native currant and gooseberry bushes that commonly serve as intermediate hosts before the disease infects new trees. Threats to these pine species include not only white pine blister rust, but mountain pine beetle, fire suppression, and climate change.
Protecting these sensitive species
The risk of losing some of Canada’s most iconic and distinctive woodlands has led to rigorous reviews at provincial and federal levels for both whitebark and limber pine. Alberta listed both species as endangered (2008), receiving protection under the provincial Wildlife Act, while B.C. put whitebark pine on the threatened list in 2013, and listed limber pine as endangered the next year. Federally, whitebark pine has been protected in Canada since 2014 under the Species at Risk Act, while limber pine is pending federal review in 2018. More than 30 bird and mammal species depend on cone crops from these trees as a food source, making these big-seeded pines a keystone species (a species whose presence and role within an ecosystem has a disproportionate effect on other organisms within the system) in many mountain ecosystems. The Clark’s nutcracker physically removes the seeds, and literally plants them to retrieve later, but forgetting some that go on to germinate. Simply put, the bird that plants the seed, grows the tree, that produces the cone, that the squirrel collects, that feeds the bear.
disturbances to western CanadA's wild forests
Logging is widespread on lower slopes where these forests are not protected within parks, and logging activity is gradually accessing higher elevations and isolated valleys as time progresses. Forests at higher elevations are cut for the occasional ski resort or mining road, but are primarily exposed to natural disturbances such as wildfires, landslides, and snow avalanches.
Humans also need these high-elevation pines to slow snow melt, and stabilize the banks of mountain streams, in order to safely inhabit downstream communities. Our ecological dependency on natural systems highlights the need for coordinated restoration initiatives to ensure these pines persist.
Building a Recovery Plan
Our societal mandate to develop recovery plans for threatened species has led to the search for blister rust resistant individuals (genotypes) as one of several key recovery strategies. Researchers have also identified a form of single-gene disease resistance in a southern Alberta limber pine population, and multi- gene resistance that slows disease expression and pathology is more widely distributed. Cone collections from disease resistant trees allows for the propagation of resistant trees.
Numerous opportunities exist for volunteers to participate in local restoration efforts. Contacting the Whitebark Ecosystem Foundation of Canada is a good place to start.
We all recreate in these high-elevation forests, and derive far-reaching benefits from them. Taking personal ownership of their restoration is a great way to ensure their persistence.
The original version of this story appears in The Alpine Club of Canada’s State of the Mountains Report 2018
Authored by: Philip J. Burton, Ph.D., R.P.Bio., University of Northern British Columbia, Terrace, British Columbia
and Vernon S. Peters, Ph.D., The King’s University, Edmonton, Alberta