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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