FIRES AND DWARF MISTLETOE IN A ROCKY-MOUNTAIN LODGEPOLE PINE ECOSYSTEM

Forests in the western U.S. are subject to a variety of pathogens, who se role in forest health is being questioned. The relationship of dwar f mistletoe (Arceuthobium americanum Nutt. ex Engelm.) and time since stand-replacing fire was determined for part of the Medicine Bow Natio nal Forest in southeastern Wyoming. Mean dwarf mistletoe rating (0-6 s cale) was found to be 0.85 in the study area as a whole and ranged fro m 0-5.82. Of 43 stands examined, 51% contained mistletoe to some degre e. Dwarf mistletoe infection was light in the majority of the sampled stands in the study area. Dwarf mistletoe infection characteristics ge nerally increased with increasing time since stand-replacing fire but were highly variable. Mean dwarf mistletoe infection characteristics g enerally increased with tree size, but were also highly variable. Chi- square analysis indicates that trees surviving the most recent stand-r eplacing fire increased dwarf mistletoe infection rates in the post-fi re stands. Dwarf mistletoe infection at the landscape scale is charact erized by infection centers, as some stands have heavy mistletoe infec tion while stands of similar age have no mistletoe infection present. If prescribed fires are used to restore the health of lodgepole pine f orests, these fires will need to be intense, stand-replacing burns. Bu t, healthy lodgepole pine forests may always contain a mosaic of mistl etoe infection centers and uninfected stands that require a spatial ap proach to health assessment. (C) 1998 Elsevier Science B.V. All rights reserved.