. A case study of a Douglas-fir tussock moth outbreak and stand conditions 10 years later. Douglas-fir tussock moth; Tree declines California; Trees Diseases and pests California. Table 3—White fir mortality by year and cause, Stowe Reservoir, 1973-75 (based on I, 725 trees living in 1973) 1 i ire r\r~ \ iTlULn Ddl K Dec Lie Year No. % No. % No. % 1973 0 0 16 1 1974 0 0 25 5 1975 0 0 3 1 Total 0 0 44 7 White fir mortality was stratified by diame- ter classes, based on the 1967 data (fig. 2). Most of the loss caused by tussock moth occurred in the 1- to 6-in
. A case study of a Douglas-fir tussock moth outbreak and stand conditions 10 years later. Douglas-fir tussock moth; Tree declines California; Trees Diseases and pests California. Table 3—White fir mortality by year and cause, Stowe Reservoir, 1973-75 (based on I, 725 trees living in 1973) 1 i ire r\r~ \ iTlULn Ddl K Dec Lie Year No. % No. % No. % 1973 0 0 16 1 1974 0 0 25 5 1975 0 0 3 1 Total 0 0 44 7 White fir mortality was stratified by diame- ter classes, based on the 1967 data (fig. 2). Most of the loss caused by tussock moth occurred in the 1- to 6-in class, but the small amount of mortality caused by bark beetle steadily increased up to the 19- to 24-in class. Trees larger than 24-in suffered no loss from bark beetles on our plots. CAUSES OF MORTALITY ii&sTussock moth. jBark beetles 1-6 7-12 13-18 19-24 24 DBH CLASSES (inches) Figure 2.—Percent mortality of white fir by classes, Stowe Reservoir, 1967. A summary of stand statistics from the 1967 cruise is given in table 4. From these data we calculated that percent of the stand (number of trees) and percent of the stand volume were killed by the tussock moth in this heavily defoliated outbreak area. When bark beetle mortality was added, about 32 percent of the stand volume was killed. Tree mortality was also summarized (table 5) for advanced reproduction (trees below 1 inch in diameter but more than 10 years old) and recent regeneration (trees less than 10 years old). This information was compared for the 1967 and 1975 cruises to show the amount of mortality caused by tussock moth and amount of postoutbreak regeneration and ingrowth for these size classes. Mortality has been high among advanced reproduction since 1967, even without defoliation. Most of these trees were suppressed and over-topped so the recent high mortality was probably caused by competition. From the difference between 1967 losses (29 percent) and 1975 losses (20 pe
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