Year of Award
Master of Science (MS)
Department or School/College
College of Forestry and Conservation
Diana L. Six
Andrew J. Larson, Anna Sala
bark beetle, cold tolerance model, Cronartium ribicola, Dendroctonus ponderosae, phenology model, Pinus albicaulis, population decline, productivity
University of Montana
In recent years, the mountain pine beetle (MPB, Dendroctonus ponderosae) has caused dramatic levels of mortality of whitebark pine (Pinus albicaulis). This keystone and foundation tree species is also being killed by the exotic fungus, Cronartium ribicola, which causes the disease white pine blister rust (WPBR). This study examines MPB productivity in whitebark pine compared to that in lodgepole pine, and also in whitebark pine of varying WPBR infection severities to determine if either of these host factors contributes to the current, dramatic MPB outbreaks in whitebark pine. To evaluate host tree effects on MPB, I tracked attack densities, emergence rates, size and sex ratio of MPB from lodgepole pine, and from healthy and WPBR-infected whitebark pine. Beetle emergence rate was higher from whitebark pine. I found no differences in beetle size between lodgepole and whitebark pine. The three populations I tracked declined precipitously during the period of study. This decline was likely caused by a cold snap in October 2009 as indicated by combined phenology/cold tolerance model results. MPB attack density was lowest on the most severely WPBR-infected trees, but emergence rates and size of beetles from these trees were greatest. Low attack rates in severely infected whitebark pine may indicate that these trees have lower defensive capabilities, while the greater emergence rates from these trees are likely due to low intraspecific competition afforded by low attack rates. Given that highly infected whitebark pine support high MPB productivity, these trees could support rapid MPB population growth when environmental conditions are favorable. It appears that whitebark pine is a better host for MPB than lodgepole pine, but whitebark pine of varying WPBR infection severity do not differ from each other in terms of beetle productivity. Therefore, the extensive MPB outbreaks in whitebark pine likely reflect the combination of both whitebark pine’s superior host quality, as well as the favorable conditions for MPB development created by a warming climate in high elevation forests.
Dooley, Edith Mary, "Mountain pine beetle outbreaks in high elevation whitebark pine forests: the effects of tree host species and blister rust infection severity on beetle productivity" (2012). Graduate Student Theses, Dissertations, & Professional Papers. 683.
© Copyright 2012 Edith Mary Dooley