396 
6 U.S. VERSUS EUROPEAN APPROACHES TO FOREST DECLINE 
INVENTORIES 
Since the late 1970’s, a regional decline, affecting 
many tree species has also appeared in Europe. In 
recent years CIR aerial photos have also been widely 
used in West Germany (Hildebrandt 1985) and other 
European nations (Scherrer et al. 1981; Zirm et al. 
1985). 
To date, inventories of forest decline in the 
United States have emphasized detection and 
quantification of trees with "hard” damage symptoms 
such as tree mortality and top or branch dieback. 
Consequently, we have been able to use relatively 
small photo scales. The photo scale currently 
recommended for tree level data is 1:8000 but aerial 
photos of considerably smaller scales have also been 
used to delineate vegetation and mortality classes 
(Table 1). 
In West Germany, on the other hand, emphasis on 
forest damge inventories has been on assessment of 
the condition of living trees; therefore, the full 
range of symptoms associated with forest declines: 
loss of older foliage, subtop dieback, discolored 
foliage, are classified on aerial photos using a 
5-class rating system. Aerial photos of a larger 
scale are normally used to resolve these more subtle 
symptoms. The most commonly used photo scales are 
1:5000 and 1:6000 (Hildebrandt 1985). 
In the United States, forest damage inventories 
have been designed to provide data on numbers of 
trees, volumes, and basal area per unit area of land 
(per acre) by various damage or decline classes. 
This has necessitated interpretation and rating of 
all trees on an aerial photo plot of known size. In 
inventories conducted in West Germany, resultant 
data is most frequently represented in terms of the 
proportion of trees or area of given species in each 
damage class (Anon 1984). These data are obtained 
by rating a fixed number of trees in a series of 
cluster plots on aerial photo sample strips 
(Hildebrandt and Kadro 1984). 
Photo interpretation keys have been developed for 
large scale CIR photos in West Germany for 
identification of tree species, including spruce and 
fir, and rating damage (Grundmann 1984; Masumy 
1984). This approach is of interest in designing 
future inventories of forest decline in the eastern 
United States. We are presently developing photo 
interpretation guidelines for separation of spruce 
and fir on CIR photos and there are indications that 
the more subtle symptoms of decline can also be 
detected. If this approach can be applied to forest 
conditions in the United States we will undoubtedly 
also be using CIR aerial photos at scales in the 
range of 1:4000 to 1:6000. 
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