. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. was convinced by his analysis of the study Person had established that Dunning's clas- ses were unsuitable for rating risk. Sal- man also noted two limitations in the 16- class system developed at this time by Keen for use in southern Oregon. First, the 16 classes made it cumbersome as a working tool, and second, it would require the r
. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. was convinced by his analysis of the study Person had established that Dunning's clas- ses were unsuitable for rating risk. Sal- man also noted two limitations in the 16- class system developed at this time by Keen for use in southern Oregon. First, the 16 classes made it cumbersome as a working tool, and second, it would require the removal of too large a volume of tim- ber for quick treatment of stands. If the forest manager was to reduce the chances of bark beetle losses, the cutting should be light enough to cover stands quickly. Salman took advantage of the observa- tions of workers making annual loss sur- veys in northeastern California in the early 1930's. They had reported that most trees killed could be characterized by various kinds and degrees of crown deteri- oration before attack. These observations were crystalized into a study by Salman in 1936, in which 973 infested and 2,026 unattacked trees were cut and carefully examined for various types of crown deter- ioration. A three-class structure was prelimin- arily established, but Salman's field crew found that four classes were better for field application. Eventually the ele- ments of high risk were described as fol- lows (Salman 1937 and Salman and Bongberg 1942) (fig. 3): —thin or sparse foliage complement, short needles, and the dying of twigs and branches were characters of the trees that become in- fested and die—active or recent top-killing infestations, the localization of branch or twig injuries, and the thinning and shorten- ing of foliage in portions of the crown also occurred in many of the trees that died—. Low Risk High Risk Figure 3.—Four stylized trees, illustrat- ing the four risk classes of the Cal- ifornia Pine Risk-Ra
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