Fires and dwarf mistletoe in a southeastern Wyoming forest

Forests in the western U.S. are subject to a variety of pathogens, whose role in forest health is being questioned. The relationship of dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) and time since stand-replacing fire was determined for part of the Medicine Bow National Forest in southeastern Wyoming. Mean dwarf mistletoe rating (0-6 scale) was found to be 0.85 in the study area as a whole and ranged from 0-5.82. Of 43 stands examined, 51% contained mistletoe to some degree. Dwarf mistletoe infection was light in the majority of the sampled stands in the study area. Dwarf mistletoe infection characteristics generally increased with increasing time since stand-replacing fire but were highly variable. Mean dwarf mistletoe infection characteristics generally increased with tree size, but were also highly variable. Chi-square analysis indicates that trees surviving the most recent stand-replacing fire increased dwarf mistletoe infection rates in the post-fire stands. Dwarf mistletoe infection at the landscape scale is characterized by infection centers, as some stands have heavy mistletoe infection while stands of similar age have no mistletoe infection present. If prescribed fires are used to restore the health of lodgepole pine forests, these fires will need to be intense, stand-replacing burns. But, healthy lodgepole pine forests may always contain a mosaic of mistletoe infection centers and uninfected stands that require a spatial approach to health assessment.