Conifer mortality associated with root disease and insects in Colorado.
Recently killed and dying trees of white and subalpine firs (Abies concolor, A. lasiocarpa), Douglas fir and Englemann spruce over 1.4 m in ht. were tallied in selected mortality centres in the San Isabel, Rio Grande, San Juan, and Grand Mesa national forests in Colorado, and examined for root disease and insect damage. More than 99% of trees had root disease, and of these more than 80% were infested with bark beetles or wood borers (most commonly Scolytus ventralis on white fir, Dryocoetes confusus on subalpine fir, Dendroctonus pseudotsugae on Douglas fir, D. rufipennis on spruce, and Buprestidae, and Cerambycidae on all species). Armillaria mellea, found on all species, and Fomes annosus [Heterobasidion annosum], found on white and subalpine firs, were the major root pathogens.