Austral Ecology (2005) 30, 103–117 Do Eucalyptus plantations host an insect community similar to remnant Eucalyptus forest? SAUL A. CUNNINGHAM,* ROBERT B. FLOYD AND TOM A. WEIR CSIRO Entomology, Box 1700, Canberra, ACT 2601, Australia (Email: saul.cunningham@csiro.au) Abstract We examined the potential of forest plantations to support communities of forest-using insects when planted into an area with greatly reduced native forest cover. We surveyed the insect fauna of Eucalyptus globulus (Myrtaceae) plantations and native Eucalyptus marginata dominated remnant woodland in south-western Australia, comparing edge to interior habitats, and plantations surrounded by a pastoral matrix to plantations adjacent to native remnants. We also surveyed insects in open pasture. Analyses focused on three major insect orders: Coleoptera, Lepidoptera and Hymenoptera. Plantations were found to support many forest-using insect species, but the fauna had an overall composition that was distinct from the remnant forest. The pasture fauna had more in common with plantations than forest remnants. Insect communities of plantations were different from native forest both because fewer insect species were present, and because they had a few more abundant insect species. Some of the dominant species in plantations were known forestry pests. One pest species (Gonipterus scutellatus) was also very abundant in remnant forest, although it was only recently first recorded in Western Australia. It may be that plantation forestry provided an ecological bridge that facilitated invasion of the native forest by this nonendemic pest species. Plantation communities had more leaf-feeding moths and beetles than remnant forests. Plantations also had fewer ants, bees, evanioid wasps and predatory canopy beetles than remnants, but predatory beetles were more common in the understory of plantations than remnants. Use of broad spectrum insecticides in plantations might limit the ability of these natural enemies to regulate herbivore populations. There were only weak indications of differences in composition of the fauna at habitat edges and no consistent differences between the fauna of plantations adjacent to remnant vegetation and those surrounded by agriculture, suggesting that there is little scope for managing biodiversity outcomes by choosing different edge to interior ratios or by locating plantations near or far from remnants. Key words: community composition, Eucalyptus, forestry, insects, ordination, plantation, species richness. INTRODUCTION Plantation forests are expected to support less diverse insect communities than natural forests. Production- orientated forests usually have low plant species diversity, which is expected to favour a lower diversity insect community (Murdoch et al. 1972; Knops et al. 1999). This effect is in part because of a direct linkage between plant species richness and insect species richness driven by host specificity, but also because of the linkage between plant species richness and struc- tural diversity of the vegetation (Koricheva et al. 2000; Haddad et al. 2001). Indeed tree plantations are distinguished by even-aged tree cohorts, and little understory or dead wood. The impact of plantation forestry on regional insect diversity depends not only on the levels of insect species richness per se, but on how similar or different these communities are from those in native forests, and on whether or not there are positive or negative inter- actions between these two kinds of habitat. Further, it is important to understand whether or not these bio- diversity impacts are influenced by the placement of these plantations in the landscape. It is predicted that the insect community which develops in a plantation will be effected by the amount of edge relative to interior and by the isolation of the habitat island (e.g. a plantation) from a source of colonists such as a forest remnant (Tscharntke et al. 2002). There are, however, only limited empirical data on insect responses to these landscape variables. For example, one study found that isolated patches have fewer species of insect predators (Zabel & Tscharntke 1998) and lower rates of parasitism (Kruess & Tscharntke 2000) and another found more insect species in isolated patches (Fahrig & Jonsen 1998). It has been suggested that even when there are effects of isolation, they might be small relative to the other determinants of insect community composition, such habitat quality (Thomas et al. 2001). The physical environment of forest edges are known to be different from the forest interior, with possible consequences for animal communities (Laurance & *Corresponding author. Accepted for publication April 2004.