Incidence and Effects of Endemic Populations of Forest Pests in Young Mixed-Conifer Forests of the Sierra Nevada

Approximately 3.200 trees in young mixed~conifer stands were examined for pest activity and human-caused or mechanical injuries, and approximately 25 percent of these trees were randomly selected for stem analyses. The examination of trees felled for stem analyses showed that 409 (47 percent) were free of pests and 466 (53 percent) had one or more pest categories. Incense~cedar contained the fewest number of pests with 133 out of 193 trees (69 percent) free of pests, and 60 trees or .31 percent with one or more pests. White fir and ponderosa pine trees had the highest percentage of pests and mechanical injuries: 64 percent (252 trees outof395), and 62 percent (93 trees out of 151), respectively. Top injury and dise'!se were the two most frequent pest/damage categories recorded among all tree species. White fir seemed most susceptible to a large number of diseases, particularly wetwood and leafy and dwarf mistletoes. White pine blister rust and cedar rust were the most frequent diseases recorded on sugar pine and incense-cedar. respectively. Most diseases were in the early stages of their infections. Bark beetles were an important pest category for white fir, ponderosa pine, and incense-cedars. Mechanical or human-caused injuries ranged from 6to II percent ofthe damage records among all mixed-conifer species. Nevertheless, pest damage on most trees was relatively minor throughout the young mixed-conifer stands and seemed to have little effect on height and basal area increment. Tree mortality averaged a little over 3 percent. The data indicate the potential problems for older mixed-conifer stands, and they identify white fir as the tree species particularly susceptible to pests and human-caused damage. Acknowledgments: We thank K. LeRoy Dolph for providing the data and Sylvia R. Mori and Sandy Young for their statistical and editorial review, respectively, of the manuscript. Cover-White flf poles killed by 5col)'tlls ventralis.