The mountain pine beetle (Dendroctonus ponderosae) is a native insect that has coevolved as an important ecological component of western forests. The beetles bore into the bark of the pine host and can cause the tree to die within a year or two. The colder climate associated with high elevation pines has generally been too extreme for mountain pine beetles to thrive, even though these pines are suitable hosts. There is documented evidence of previous mountain pine beetle outbreaks in high elevation five needled pines, particularly whitebark pine. In some cases, beetle populations have increased in lower elevation lodgepole or ponderosa pine stands and moved into adjacent, higher elevation five-needled pine stands. In other cases, favorable stand and climatic conditions have contributed to beetle population increases.
Today, epidemic outbreaks of mountain pine beetle in high elevation whitebark pines (Pinus albicaulis) stands has become an increasing concern and a contributing factor to the decline of this susceptible host type in some locations. A combination of factors may be responsible for these unprecedented attacks, however, more information and research is needed about mountain pine beetle ecology in high elevation sites.
Recently, the beetles have been noted in forests at elevations above 10,000 feet. Some believe that as ambient air temperatures increase, the high elevation forests will be challenged more frequently by bark beetles.
Another factor associated with the recent increase in beetle infestations in high elevation forests may be fire suppression tactics resulting in a greater abundance of dense late successional forests. This provides more favorable stand and tree conditions for the beetles resulting in increased scale and frequency of beetle infestations.
Beetles prefer dense stands of older and larger trees; which results in abundant tree mortality of the susceptible host component. These same trees often are the primary cone producing trees within these high elevation sites. Reduced seed production can impact regeneration capabilities and wildlife that depend on those seeds as a vital food source. Unlike white pine blister rust however, bark beetles do not affect the viability of young seedlings or saplings.
Other beetles have been noted in high elevation five-needled pines, the impacts of which have been generally localized. For example, Pityophthorus beetles have seen in whitebark and foxtail pines (Pinus balfouriana). Ips beetles and red turpentine beetles have been seen in whitebark pine. Some cone and seed insects as well as numerous twig beetles have also been observed in the high elevation five-needled pines.
Sources: 99, 97, 98