Except for the Dixie National Forest, the serious concentrations of limb rust damage that remain toda 

 are in recreational and wilderness areas. Such infection centers are found in Rocky Mountain National 

 Park near Estes Park, Colorado; near several main points of attraction on both rims of Grand Canyon 

 National Park; in San Jacinto Wild Area of the San Bernardino National Forest; in Big Pines Recreation Area 

 of the Angeles National Forest; and in Mammoth Recreation Area of the Inyo National Forest. Probably 

 most serious is the outbreak in Bryce Canyon National Park, where limb rust is common along at least 80 

 percent of the canyon rim . 



BRYCE CANYON SURVEY 



Most reports of limb rust damage have been based on general observation. To provide more exact 

 data on incidence of limb rust and other problems in a high-value recreation area, especially on the relation 

 of limb rust to tree size and to bark beetle attack, part of W. D. Chick's 1935 survey line in Bryce Canyon 

 National Park was re-run in 1965 by personnel of the National Park Service and the Forest Service. 



Unfortunately, the 1935 and 1965 transects were not exactly comparable. They probably failed to 

 coincide by several yards along most of their lengths, and the 1965 survey was run for only 4.0 miles as 

 compared to 12.6 miles covered by Chick's survey. However, the 1965 survey included much more than 

 half of the ponderosa pine included in Chick's survey, the southern part of which ran mostly through fir and 

 Douglas -fir stands. 



The transect belt was 66 feet wide and extended from a point on the canyon rim about 1 mile north - 

 northeast of Fairyland Viewpoint southward and southwestward to the junction of the Inspiration Point and 

 Paria View roads. The northern 2. 1 miles of the 1965 sample run east of the main Park road through pine 

 stands in which relatively little pest control work has been done during the past 30 years. The adjoining 

 southern 1.9 miles lie mostly west of the main road. In this area, intensive control work was directed 

 against dwarfmistletoe and bark beetles during the 1950's. Control measures included the use of pruning, 

 silvicides, and insecticides. Some limb rust infected trees in this area were heavily pruned. 



Both the 1935 and 1965 surveys used somewhat subjective standards to categorize limb rust infections. 

 "Early infection" indicates that limb rust was present but that only one or two primary branches of the tree 

 had been killed; "intermediate infection" indicates that several branches or a small group of branches had 

 been killed; "advanced infection" indicates that a large section of the crown was dead; and "near-lethal" 

 indicates that more than 80 percent of the crown was rust-killed and the tree was likely to die within 2 years. 



The 1965 surveyors probably were more conservative inasmuch as they were required to see spore 

 sacs of the causal fungus before rating a tree as rusted. Chick's file report indicates that such was not 

 required in 1935, but only that it was "often possible" to see spore sacs. Apparently all spike-topped trees 

 were judged as rusted by the 1935 surveyors. This probably accounts for one or two percentage points' 

 difference between the results in these surveys. 



Pines smaller than 6 inches d.b.h. were not included in Chick's survey. These were found to be 

 completely free of limb rust in the 1965 sample although occasional infections on small trees were observed 

 outside the transect. 



From table 1 it appears probable that limb rust is somewhat less common now in the northern part of 

 the Park than it was throughout the Park in 1935. Judging from this difference plus the observed similarity 

 of limb rust infection in the northern and southern parts of the Park (in spite of the different elevations and 

 different percentages of ponderosa pine in the stands), it seems likely that there has been an overall 

 decrease in the percentage of rusted pines during the past 30 years. 



This putative decrease is in line vwth the relative shift away from "early infections" and toward "ad- 

 vanced infections": it appears that many infected trees have died during the 30 years but that infection has 

 not kept pace. Most of today's "advanced infections" are "early," "intermediate ," or even "advanced" 

 infections of 30 years ago, judging from Mielke's data (11) on growth rates and from the one photographic 

 series that goes back that far. Three photographs of one tree taken in 1935, 1947, and 1959 (2) show that a 

 pine with 30 percent of its crown killed (an "advanced" infection) can still be alive 24 years later. This tree 

 is shown in a photograph taken in 1948 (fig. 1). 



6 



