. Bark beetle and wood borer infestation in the Greater Yellowstone Area during four postfire years. Bark beetles Yellowstone National Park; Wood borers Yellowstone National Park; Trees Diseases and pests Yellowstone National Park; Forest fires Yellowstone National Park. r 40 20 Douglas-fir data 1991,1B92 .11 1-20 21-40 41-60 61-80 81-100 Total Percent Basal Circumference Killed Figure 12—Percent insect infestation of Douglas-fir by fire-injury class. Douglas-fir mortality 1991,1992 Weighted Regression Analysis V- + *X R"2 - Percent Basal Firs injury Figure 14—Relationship
. Bark beetle and wood borer infestation in the Greater Yellowstone Area during four postfire years. Bark beetles Yellowstone National Park; Wood borers Yellowstone National Park; Trees Diseases and pests Yellowstone National Park; Forest fires Yellowstone National Park. r 40 20 Douglas-fir data 1991,1B92 .11 1-20 21-40 41-60 61-80 81-100 Total Percent Basal Circumference Killed Figure 12—Percent insect infestation of Douglas-fir by fire-injury class. Douglas-fir mortality 1991,1992 Weighted Regression Analysis V- + *X R"2 - Percent Basal Firs injury Figure 14—Relationship of insect infestation to basal fire injury of Douglas-fir. 100 injury (fig. 13). Pseudohylesinus nebulosus was the second most common bark beetle infesting Douglas- fir, followed by the wood borers. Regression relation- ships between basal girdling by fire and infestation are shown in figure 14. Our sample of Engelmann spruce for 1991 and 1992 combined show that percent of trees across all injury classes were infested by insects. Infestation ranged from percent of the uninjured trees to percent of trees having 41 to 60 percent of their basal circumference killed by fire (fig. 15). Spruce beetle accounted for almost one-half of the infested trees ( percent). Infestation by spruce beetle ranged between percent of uninjured trees to per- cent of trees having 41 to 60 percent basal girdling; the infestation is usually limited to the lower 20 ft of the trunk (Schmid 1976). Therefore, bark scorching in the injury classes exceeding 60 percent girdling of the basal circumference may deter beetles from in- festing such heavily injured trees (fig. 16). Our samples of subalpine fir (134 trees) and white- bark pine (144 trees) were too small to draw meaning- ful conclusions about insect response to different fire injury levels. However, it does appear that insects, mostly wood borers, prefer the more severely injured subalpine fir (fig. 17). No strong relati
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