orest 
were 
ns, 
t no 
ot- 
that 
mples 
the 
an 
was 
ydney 
tes. 
uded 
he 
he 
oil 
The 
he 
by 
ASSESSMENT OF DIEBACK 
In late 1972, at the request of the Norfolk Island Administration, 
the Australian Forestry and Timber Bureau undertook to investigate and 
report on the occurrence of the dieback and to suggest a course of action 
for the administration. 
The assessment incorporated two main activities - 
(i) an examination of aerial photographs of the island, and 
(ii) a site inspection to study the symptoms and associated 
land use practices. 
In addition to the information gathered in these activities, the 
Bureau had access to the large number of reports concerning vegetation, 
geology, soils, water resources, land use, forestry potential, development 
potential, etc. which have resulted from numerous studies carried out 
over the years. Many historic ground photographs, some more than 70 
years old, were also available. 
Two missions of aerial photography existed at the time, a black and 
white 1:12 500 scale cover taken in 1944 and a colour 1:4000 scale cover 
taken in 1968. The early photography was of little value in looking for 
dieback symptoms because of scale and film type, however, it was useful in 
providing a statement of current land use patterns and development on the 
island. The 1968 colour photography was obtained for use in the prep- 
aration of a detailed vegetation map of the potential national park site. 
Benson (1974) provided details of the mission which resulted in a set of 
photographs of outstanding colour fidelity and resolution. The 180 
photographs covering the island were exposed in a Zeiss RMK camera fitted 
with a 650 mm focal length lens. The format was 230 x 230 mm. 
Because of the large scale of the photographs, individual pine trees 
were clearly visible with crown images ranging from 1 to 3 mm in diameter. 
The dieback symptoms mentioned earlier were clearly recognisable since the 
dead branches were considerably lighter in colour than the healthy branches 
and they contrasted sharply with the green understorey or ground vegetation. 
These symptoms were readily separable from the appearance of healthy trees 
carrying infestations of the bearded moss, Usnea. 
The crowns of all mature trees were examined and boundaries of 
consistent areas were outlined according to the following severity of 
dieback scale: 
H - healthy - no dieback symptoms visible 
L - lightly affected - less than 50$ of mature crowns 
showing some signs of ill health 
S - severely affected - more than 50$ of mature trees 
dead or having dead portions, 
or with very thin crowns carrying 
considerable quantities of bearded 
moss.