Combined Effects of a Changing Climate Drive Mountain Pine Beetle Outbreaks
Despite its tiny size, the mountain pine beetle (MPB)is responsible for tree mortality across millions of acres in western North America, resulting in a transfer of carbon that exceeds that of fire-caused tree mortality. The MPB's survival and success is directly linked to evolved physiological adaptations that allow them to survive excessive heat and cold in their habitat beneath the bark of pine trees. For example, they produce antifreeze compounds to survive cold temperature and only grow when temperatures reach critical warm thresholds. These adaptations, which vary depending on the elevation and latitude of the forest, promote population survival. While MPB can exist at low levels for years in a forest, population growth to the outbreak stage requires "triggers," in addition to an excessive amount of food in the form of relatively large pine trees across large landscapes. Favorable temperature and reduced precipitation that stresses host trees and their ability to ward off a MPB attack have triggered outbreaks in recent years. No single factor is responsible in all forests, but instead it involves some combination of warming winter and summer temperatures, severe drought and host tree resistance, in addition to landscapes of suitable pine trees. Although MPB success is based on evolved physiological adaptations, not all populations of MPB across the western U.S. may be able to take advantage of continued increases in temperature. Field-validated models that describe the intricate temperature-dependent processes that foster MPB success allow scientists to predict forest vulnerability in a changing climate.
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