WSP10425 - Laserfiche WebLink

Home Browse Search

00J2:J8 Tree Diseases and Insects Trees, like people, succumb more readily to the ills which befall them as they grow older. The extensive stands of trees over 150 years of age in the Unit are quite susceptible to a variety of insects and diseases. Prior to the advent of forest fire control at the turn of the century, lightning and man caused fires burned widespread areas of old growth forests, resulting in the periodic reestablishment of young disease free stands. Now, with the life span of the trees prolonged through fire control, insects and diseases become a dominant factor in determing health and growth form of the trees. Dwarf mistletoe, a parasitic plant which saps the vigor of the infected host tree, is widespread although the seriousness of infestation varies. Ponderosa pine and Douglas-fir trees are heavily infected in some locations. Milteltoe spreads from tree to tree by shooting its sticky seeds out of the mistletoe berries-sometimes flying as far as 75 feet. The seeds stick to the trees allowing the mistletoe to continue spreading through the forest. Another invader of age-weakened forest stands is the bark beetle. Many kinds of bark beetles occur in low or endemic numbers throughout the forest. Each species of beetle attacks a particular species of tree. As a stand declines in health, the beetle populations tend to increase rapidly and epidemics may result. Healthy trees sometimes resist the boring insects by secreting pitch or sap, but those trees weakened by mistletoe, old age or other factors are less likely to survive. Western bud worm in white fir, Douglas-fir and Engelmann spruce, and Western (Great Basin) tent caterpillar in aspen, become epidemic at times. Ips beetle in young pine stands occasionally becomes epidemic in very localized areas. "Diseases" such as fungi, rusts, and so on attack trees of all species and all ages. Again, the older trees are generally affected more than the younger trees. The diseases that primarily attack older trees usually cause wood decay. Diseases that usually attack younger trees generally effect the rate of growth and the growth form. Forest management practices can be substituted for the role of wildlfire to maintain younger and more vigorous forest stands. I n some locations, such as in areas where access is very poor or values very low, where the trees are being attacked by insects, nature will undoubtedly be allowed to run its course. The careful and judicious use of fire under controlled circumstances holds promise as a management tool.