Possum (trichosurus Vulpecula) Densities and Impacts on Fuchsia (fuchsia Excorticata) in South Westland, New Zealand

New Zealand Journal of Ecology (1998) 22(2): 197-203 ©New Zealand Ecological Society possums (Pekelharing and Batcheler, 1990), the palatability of the plant species relative to others in the area (Brockie, 1992; Allen, Fitzgerald and Efford, 1997), the species composition and age structure of the plant population (Payton, 1987, 1988), other environmental stresses (Stewart and Veblen, 1982), plus the interactions between all these. Despite this complexity managers need some simple “rule-of-thumb” measures of impacts or of possum densities that they can use as intervention thresholds for initial or repeated control. Tree fuchsia (Fuchsia excorticata J.R. et G. Forst.) is eaten by possums in south Westland (Owen and Norton, 1995), and is susceptible to possum damage (Rose et al., 1993b). Its condition in these forests can therefore act as a bioindicator or early warning of the need for possum control. In this paper we compare the amount of damage and mortality to fuchsia over 5 years at five sites in south Westland where possum densities varied from near-zero to high (trap-catch rates of over 40%) and where the sites each had different colonisation and control histories. The hypotheses tested were that possums defoliate and kill fuchsia, and that more possums kill fuchsia more quickly. We tested these hypotheses by comparing the condition of fuchsia canopies, indexed by an estimate of their foliage cover, with an index of possum density, and by one “experiment” where possum densities at one site were markedly reduced by a commercial fur trapper. Introduction