Possum browsing - The downside to a eucalypt hybrid developed for frost tolerance in plantation forestry

Abstract

Eucalyptus hybrids are being investigated for use m plantation forestry to incorporate frost tolerance into marketable species. Five large field trials at four altitudes in Tasmania, southern Australia, were established to measure performance of E. gunnii, E. globulus, their F1 hybrids and E. nitens, the species currently used at higher altitudes. Four of these trials were browsed by brushtail possums (Trichosurus vulpecula), allowing inheritance of resistance to browsing between cross-types to be determined. Inheritance in the F1 hybrids was found to be additive, with partial dominance towards the less resistant E. gunnii, particularly at lower altitudes. E. nitens sustained similar damage levels to E. globulus. Field damage results were compared with relative intake of foliage in feeding trials using captive possums. Relative intake of foliage in feeding trials was similar to field damage patterns provided the trials were short-term (3-4 days). Such feeding trials could, therefore, be used as preliminary bioassays of resistance. E. gunnii × E. globulus F1 hybrids did not grow as rapidly as E. nitens and they were more damaged by possums. This means that E. nitens should generally remain the species of choice for forestry at high altitudes in southern Australia, particularly in areas where brushtail possum damage is not controlled. However, there may be a niche for E. gunnii × E. globulus F1 hybrids or even advanced generation hybrids in specific environments outside Australia where winter temperatures are too cold for E. nitens to survive, and where possum browsing does not occur.