Relationships between herbivore abundance and browsing damage in Tasmanian eucalypt plantations

In Tasmania, Australia, eucalypt seedlings growing in commercial forestry plantations are often damaged by mammalian herbivores. There is presently a poor understanding of (i) the relationship between the abundance of herbivores and damage levels; and (ii) the effect that 1080 poisoning, the most frequently employed damage control technique, has on herbivore abundance. In this study, the abundance of four herbivore species was monitored at 35 first year eucalypt plantations. Forestry companies carried out 1080 poisoning operations at 28 of the plantations and no damage control was attempted at the remaining seven. When average scat deposition rates for each herbivore were regressed against levels of browsing damage, no significant relationships were observed for the Bennett's wallaby, pademelon or rabbit. However, there was a highly significant linear relationship (r2 = 0.537) between damage severity and average scat deposition rate for the brushtail possum. This suggests that managers may need to review the importance of this species as a contributor to damage. Poisoning operations resulted in an initial and sustained reduction in the abundance of pademelons on plantations. Poisoning did not result in an initial reduction in the abundance of the Bennett's wallaby and possum. However, in the long term, poisoning reduced the rate at which the abundance of these species increased. Poisoning had no apparent effect on rabbit abundance.