The impact of browsing by introduced brushtail possums on mixed beech—broadleaved forests in South Westland was estimated from the amount of conspicuous canopy dieback present in 1989- 1990. Aerial and ground-based reconnaissance in all catchments indicated most canopies (84%) were intact. The remaining 16% of canopies were affected by conspicuous dieback, principally of southern rata (Metrosideros umbellata) and/or fuchsia (Fuchsia excorticata).
The amount of conspicuous canopy dieback in all central Westland southern rata-kamahi forests east of the Alpine Fault, between 500 m altitude and treeline, was assessed and mapped from aerial photographs taken in 1984-85 and verified by aerial reconnaissance of selected areas in 1988. At least 20% of all canopy trees, predominantly southern rata (Metrosideros umbellata) and Hall's totara (Podocarpus hallii), were dead in 1984-85.