Predicting Future Spruce Beetle Infestations
In recent decades, bark beetle disturbances have been increasing in the Nation's forests. Although the increased rates of tree mortality have been attributed to the influence of warming temperatures on bark beetle life cycles, more research is needed to determine whether other potential factors exist and how those factors will change with the climate. As cause and consequences of spruce beetle infestation are important to the management of Engelmann spruce forests, Forest Service scientists modeled the effects of increased temperatures and changing forest stand conditions, such as density and species composition, on the likelihood of spruce beetle infestation over time.
Global climate change scenario models were used to determine future temperatures, which were combined with forest stand conditions to make predictions of future beetle infestation. Results show that under all climate change scenarios, the percentage of spruce forest likely to be infested by spruce beetle increased, and the increase was most pronounced in the year 2080, when anywhere from 16.2 to 32.3 percent of forests in the Interior West could be infested.
Temperature and stand conditions were equally important predictors. In particular, the amount of mature Engelmann spruce in a stand, in combination with increasing temperatures, greatly increases the likelihood of spruce beetle infestation. Although the amount of potential spruce beetle activity is predicted to increase, it is important to note that no model predicted the total loss of the spruce resource.
These results corroborate previous studies that were conducted on the mountain pine beetle in Western North America. Findings are being incorporated into management guidelines for silviculturists who wish to mitigate spruce beetle infestation by modifying the density or composition of Engelmann spruce forests in the Interior West.
Forest Service Partners