Ab. Rose et al., IMPACT OF INVADING BRUSHTAIL POSSUM POPULATIONS ON MIXED BEECH-BROADLEAVED FORESTS, SOUTH WESTLAND, NEW-ZEALAND, New Zealand journal of ecology, 17(1), 1993, pp. 19-28
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%) w
ere intact. The remaining 16% of canopies were affected by conspicuous
dieback, principally of southern rata (Metrosideros umbellata) and/or
fuchsia (Fuchsia excorticata). Major dieback nuclei were located in t
he three areas with the longest history of browsing by possums, which
had spread from three known liberation centres. At each dieback nucleu
s, the amount of dieback reflected the abundance of possum-preferred c
anopy species. Because South Westland forests contain lower proportion
s of such species, they are less susceptible to dieback than the conif
er-broadleaved forests of central Westland. However, the present low a
mounts of dieback in South Westland mainly reflect low overall possum
densities and a short period of occupation. The occurrence of key poss
um-preferred species indicates that about one-third of the forests cou
ld develop conspicuous canopy dieback if possum numbers increase and 4
4-94% are susceptible to canopy and/or understorey depletion. By 1992,
the few areas selected for sustained possum control effort in Westlan
d under-represented the range of forest composition. However, recently
boosted funding for possum control has provided the opportunity to pr
otect representative forest tracts before the onset of widespread ecos
ystem depletion in South Westland.