Susceptibility of some Eucalyptus species and their hybrids to possum damage

Common brushtail possums (Trichosurus vulpecula) are a significant vertebrate pest of eucalypt plantations in Tasmania; their browsing damage can cause loss in growth, reduced seedling survival and deformities. Possum damage could therefore become a serious problem in Australia's rapidly expanding eucalypt plantations. In addition, expansion of plantation areas is projected to include drier zones, where inter-specific eucalypt hybrids may play an important role. However, hybrids are currently being developed with little knowledge of their resistance to pests. This study examined the susceptibility to browsing by common brushtail possums of a range of eucalypts (Eucalyptus bicostata, E. globulus, E. gunnii, E. nitens, E. morrisbyi and E. ovata) and their F1 hybrids in four separate field trials in Tasmania. The Tasmanian endemics E. gunnii and E. morrisbyi were extremely susceptible to browsing whereas the other four species were relatively resistant. Within E. globulus, significant differences in damage between provenances were also detected. Field damage on interspecific F1 hybrids was generally intermediate in crosses between susceptible and resistant eucalypt species. While the exact degree of susceptibility varied, crossing a relatively resistant species with a highly susceptible species resulted in a significant increase in the susceptibility of the F1 hybrid compared with that of the resistant species. Only the hybrids between the two major plantation species E. nitens and E. globulus were significantly more susceptible to browsing than either the E. nitens or E. globulus controls, which were both relatively resistant. In practical terms, the present study indicated that possum susceptibility is an important factor to consider when investigating the potential of pure species and their hybrids for commercial use. Keywords: wildlife; damage; Eucalyptus; inter-specific hybrids; possums; Trichosurus vulpecula; Tasmania