(Batini 1973) . 
This success is due to two main factors. Firstly 
a high proportion of the understorey of this forest is sus 
ceptible to P. cinnamoml and its death produces a marked 
increase in surface reflectance with a correspondingly 
marked decrease in tonal density of the aerial photograph. 
This is accentuated by the reduced leaf density of the 
jarrah overstorey and the boundary where trees are affected 
coincides quite closely to the tonal change of the photo 
graphs. Secondly, in the northern areas, much of the 
dieback is well established, imposing more definite patterns 
.of infection which act as aids to the detection of less