Interactions between herbivores, vegetation and eucalypt tree seedlings in a plantation forestry environment

Abstract

Summary Non-lethal management methods for reducing mammal browsing damage to Eucalyptus seedlings during plantation establishment are currently being investigated in Tasmania, Australia. One method is use of selective retention of non-seedling vegetation in plantations. To assess its potential, information is needed on how herbivores use such vegetation and whether it has positive or negative effects on browsing and growth of commercial tree seedlings. We quantified the populations of five mammalian herbivore species in and around a spot-herbicided E. nitens plantation during its establishment. We also investigated several aspects of the interactions between those mammalian herbivores, insect herbivores, tree seedlings and non-seedling vegetation. We found that overall population densities were high for red-bellied pademelons (Thylogale billardierii) and red-necked wallabies (Macropus rufogriseus rufogriseus), but very low for common brushtail possums (Trichosurus vulpecula), common wombats (Vombatus ursinus) and the introduced European rabbit (Oryctolagus cuniculus). Population densities of the five mammalian species did not change in response to planting E. nitens seedlings. Dominant vegetation in the plantation was grass, then forbs and non-grass monocots. Herbivores ate a large proportion of available plantation vegetation in unfenced plots. Mammal browsing had little effect on survival of E. nitens seedlings 15 weeks after planting, but significantly reduced their growth. In unfenced plots, insects, mainly Heteronyx spp., caused twice as much damage to seedlings as browsing mammals. The absence of mammalian browsing in fenced plots, which resulted in high grass cover, was associated with reduced insect damage to seedlings.