Mountain pine beetle

The mountain pine beetle (MPB) is a native insect of western North American forests. From time to time, MPB populations increase to such high levels that they create major forest disturbances.

The current beetle epidemic, which started in British Columbia in the early 1990s, has killed extensive areas of lodgepole pine, the province’s most abundant species, and is successfully attacking jack pine in Alberta. Most pine species are suitable hosts for MPB, including the dominant boreal and eastern pine species.

The extensive and rapid damage caused by MPB epidemics affects many forest values and the economic well-being of communities that depend on forest resources. In the 12-year period from 1998 to 2010, MPB killed more than 700 million cubic metres of pine in British Columbia, over 50% of the province’s commercially important pine.

The cumulative area of mountain pine beetle spread in British Columbia and Alberta

Status

Although beetle populations are still increasing in some locations and continuing to kill pines, the current MPB epidemic in British Columbia peaked around 2005 in terms of annual volume of timber killed. The cumulative area of pine forest affected by the MPB epidemic has now reached an estimated 17.5 million hectares—an area more than twice the size of New Brunswick.

In British Columbia, the beetle epidemic now ranges from well north of Fort St. John, south to the United States border, and from Terrace in the west to the British Columbia/Alberta border in the east.

The infestation has expanded in Alberta, where the beetle is now well established along the eastern slopes of the Rocky Mountains and west-central Alberta. Much of this expansion is in novel habitat for the beetle; only the southern tracts of the eastern slopes have a recorded history of MPB outbreaks.

Influencing factors

The spread of MPB into west-central Alberta and beyond its historical geographic range is thought to be the result of two main factors:

• Moderations in climate conditions over the past decade – The moderate climate conditions have favoured both higher overwinter survival rates of beetles and the long-distance dispersal of adult beetles from central British Columbia across to Alberta.
  
  In 2009, for example, a significant proportion of beetles in local populations survived the winter around Lesser Slave Lake. This situation, combined with a major inflight of beetles from British Columbia, saw the leading edge of the epidemic move farther east to Calling Lake in central Alberta.
  
  Frequent hot, dry summers have drought-stressed the trees during the growing season. As a result, their ability to defend against beetle attack is greatly reduced.
• Forests with unnaturally high percentages of old trees – Nearly a century of forest fire suppression has resulted in forest landscapes made up of a high percentage of old trees. Typically these trees are of a larger diameter, with greater phloem layers providing more abundant habitat for beetles than smaller-diameter trees do. At the same time, however, the declining vigour of the older trees means they are less able to resist beetle attack.

Outlook

In British Columbia, the annual area of pine forest newly infested by beetle is expected to continue to decline as the outbreak collapses. The current estimate is that 61% of the provincial pine volume will be killed by 2021, when the infestation has largely subsided.

In Alberta, large areas of mature pine forest along the eastern slopes of the Rockies are highly vulnerable to beetle attack. Recent cold winters and management efforts to control populations are together slowing the rate of beetle spread. Still, the area of pine forest being attacked by beetles in Alberta is increasing.

Future eastward expansion of the MPB will depend on:

• ability of the beetle to survive the winters
• frequency of summer drought
• suitability of boreal forest pine stands to host the beetle, and
• effectiveness of intensive efforts to control beetle populations

The boreal forest structure (e.g., timber age-class distribution and species mix) and climatic conditions make the boreal forest relatively less suitable habitat for the MPB than the even-age lodgepole pine–dominated stands characterizing the current infestation in British Columbia and Alberta. However, if climate patterns change to favour overwintering beetle survival, the threat of eastward expansion will increase, with boreal jack pine forests the next to be extensively infested by the mountain beetle.