. 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. Figure 7A.—Tree shows no from 1942 (left) to (From Furniss 1954.) change in risk 1953 (right). Contingent Research After the California System was estab- lished, several studies analyzed, explained, qualified, or elaborated the principles behind risk; six of these are worthy of brief review. Changes in Risk The question was logically a
. 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. Figure 7A.—Tree shows no from 1942 (left) to (From Furniss 1954.) change in risk 1953 (right). Contingent Research After the California System was estab- lished, several studies analyzed, explained, qualified, or elaborated the principles behind risk; six of these are worthy of brief review. Changes in Risk The question was logically asked about the permanence in the risk class of a tree, does the risk of a tree tend to in- crease gradually (or quickly), does it remain fairly constant, or does it even decrease? Eaton (1941) initiated a photographic study to answer these questions. Forty- eight trees representing the four risk classes were selected for periodic photog- raphy. Furniss (1954) reports the follow- ing results after 13 years: Accidentally cut 5 Killed and showed increase in risk 11 Still alive 32 The 32 trees still alive showed as follows: An increase in risk 2 No change in risk (fig. 7A) 3 A decrease in risk (fig. 7B) 27. Figure 7B.—Tree shows decrease in risk from 1942 (left) to 1953 (right). (From Furniss 1954.) 63. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Forest Service; Society of American Foresters. Entomology Working Group. [Washington, D. C. ?] : U. S. Dept of Agriculture, Forest Service, [1981]
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