The long-term and large-scale effects of the establishment of an exotic plantation on species of native forest beetles and butterflies

Abstract

The influence of the land type between patches of remnant vegetation on species' survival is now widely acknowledged. From the species’ perspective, this land could be hostile (defined as a matrix) or amenable (defined as new habitat). In this thesis, I was interested in whether species were favoured or hindered by fragmentation of their natural Eucalyptus forest habitat into remnants surrounded by a pine plantation and the mechanisms behind their responses. I took advantage of the Wog Wog Habitat Fragmentation Experiment, in Australia, to investigate the response of beetles and butterflies to this landscape change. In a large scale edge effects study, I demonstrated that the effect of a Eucalyptus forest-pine plantation edge was widespread for the beetle community and that phytophagous beetles respond predictably to vegetation change along the edge gradient. Furthermore, I highlighted that many species responded to edge effects up to and beyond the scale tested (1000 metres). In a study of butterflies at the Wog Wog Habitat Fragmentation Experiment, I demonstrated that butterfly species were richer in the pine plantation than the remnants and continuous forest. This suggested that the pine plantation offers new and possibly preferable habitat for butterflies than the corresponding native Eucalyptus forest. Furthermore, there was evidence for a mass effect within the remnants, with the pine plantation potentially boosting species richness and abundance of common species in the remnants when compared with the controls. Revisiting carabid beetle species studied originally between 1985 and 1992, I found that responses in the long term (more than 25 years post-fragmentation) contrasted with those in the short term (five years post-fragmentation). Long-term species’ responses were driven by the changing pine plantation matrix, which offers additional habitat resources and a habitat structure favourable to carabid populations both in and around remnant native Eucalyptus forest fragments. I used specimens of two carabid beetle species collected at Wog Wog to measure morphological change through the history of the experiment. Changes implied that one species increased its dispersal ability in response to the plantation landscape. This change was likely in response to the different ground structure in the pine plantation in tandem with the increased habitat that it provides. Collectively, the papers in this thesis demonstrate that plantations can have both positive and negative effects for species. Species' responses to plantations changed over time as a result of a number of interacting factors such as changes in habitat resources and structure and species interactions. The trees at the Bondi State Forest are currently reaching maturity and are due for harvesting over the next few years. This suggests that many beetle and butterfly species will lose access to resources in the plantation resulting in their decline. This will likely impact species at over 1000m beyond the edge of the plantation, which includes those in…