447 -
ying an
n are
if ied
Table 2.
A further measure of reliability is the ability to
detect a source of P. cinnamomi infection. Although errors
in detecting the exact boundaries of an area of dieback will
lead to errors in area, it is important to detect the source
of infection whether or not the boundaries can be accurately
determined. In the area checked in the field all nine die-
back patches found were detected on the 1s 3,000 photos,
while only four of the six patches found in the area covered
by the 1: 40,000 photos were detected.
000
The study has shown that 70 mm 1s 3>000 colour
photography is a considerable advance on conventional
1s 40,000 black and white photography for the detection of
dieback disease in western Australia. Sources of infection
and the boundaries of incipient dieback are detected with a
ield
Pansect
ne tres)
high degree of reliability. Advanced dieback is detected
with a satisfactory degree of reliability.
On the 1s 40,000 photographs, the ability to
detect centres of infection and to define boundaries of
14,000
; 850
0
Type B and associated Type 0 can still be regarded as un
satisfactory despite the improvements made by the additional
information from the 70 mm strip lines. So far as new
infections are concerned, an anomaly exists in the results.
640
r 800
0
It would appear that the 1s 40,000 photos are as reliable as
the1s 3>000 photos for this purpose (see Table 1) . However
this is due to the fact that several infections detected on
the 70 mm photos were linked along watercourses, as discussed
earlier. These watercourses were in fact infected but they
could not have been detected without the aid of the 70 mm
0
0
200
i
photographs. Where infections are isolated, Type G cannot
be detected with any degree of reliability on the 1: 40,000
photos •
0
DISCUSSION
Although the large-scale phase (70 mm) has proved
successful, the small-scale phase requires improvement if
the system is to be fully effective in the southern jarrah
forest.
Colour infra-red photographs could be expected to
provide some improvement in detecting differences in total
leaf density. Although a trial of small-scale colour
infra-red photographs has been carried out, difficulties are
being experienced in obtaining a satisfactory colour balance.
Further trials with the 70 mm photography are also
required to determine the smallest scale at which individual
understorey specimens can be identified. If a smaller scale
is possible, then the increased coverage should improve
results by providing a better picture of the pattern of the
deaths in the understorey.
Apart from mapping, the project has emphasised