Trees susceptible to the Mountain Pine Beetle (MPB) include lodgepole, limber, ponderosa, scotch and white pine.  Blue and Engelmann spruce are susceptible to a related Spruce Bark Beetle.  Douglas fir are susceptible to a related Douglas Fir Beetle.  These beetles share many of the same characteristics as the Mountain Pine Beetle.

MPB historically have attacked larger diameter, older trees.  The old standard for minimum size the MPB prefer to infest has been eight inches diameter at breast height (DBH).  In the current epidemic this standard has proven to be inaccurate.  The minimum susceptible diameter depends on the level of infestation and the overall forest health.  In overcrowded forests experiencing a high infestation rate we are seeing MPB in trees down to two inches DBH.  In forests that have been properly thinned, the average minimum susceptible diameter increases to five inches DBH.

The main factor that affects MPB infestation rates is the health of the trees.  Unhealthy trees release a stress signal that attracts MPB.  Tree health is related to available moisture, nutrients and sunlight.  The main cause of stress stems from competition among trees in overcrowded forests.  Drought also reduces the available water and weakens the trees.

MPB are attracted to areas with too high of a basal area.  Basal area is described as the tree mass per acre.  When areas have too much mass for a given amount of water and nutrients the trees become weak.  Contact us to have the basal area of your forested property calculated to help determine the susceptibility of your trees to MPB attacks.

Click here for a tree identification tip sheet.