Epigaeic beetle communities of the Green Triangle plantation landscape,southern Australia: effect of remnant size,vegetation quality and structural complexity

Across the Green Triangle plantation landscape of south-eastern South Australia and south-western Victoria there remain remnant patches of native vegetation which vary considerably in both size and vegetation quality. This study focused on how the vegetation quality and or size of remnants embedded within the bluegum (Eucalyptus globulus) plantation landscape influence the local ground-dwelling Coleoptera (beetle) assemblages found within them. The aim was to particularise those remnant characteristics (in terms of size and vegetation quality) that are likely to result in the most effective protective management of local remnant beetle biodiversity. Pitfall sampling was carried out over a 13-month period. All beetles sampled via pitfall traps were identified to family level, and the three most abundant beetle families (Carabidae, Staphylinidae and Tenebrionidae) identified to genus. Remnant vegetation was assigned to one of the four quality categories (as defined by the Land for Wildlife (LFW) method), and structural attributes of the vegetation surrounding each trap were also measured.

Different beetle taxa responded independently to remnant vegetation quality and size, and to the measured vegetation structural variables. Mean beetle family abundance and estimated richness increased with decreasing remnant vegetation quality. However, when Carabidae, Staphylinidae and Tenebrionidae beetle families were analysed separately at genus level, taxa responded independently to vegetation quality and size. Furthermore, different vegetation structural variables such as the percentage cover of litter and shrubs as well as the number of overstorey stems were correlated with estimated richness of different beetle taxa. Beetle abundance was significantly influenced by mean litter depth and shrub and litter cover. This study also showed that remnants of different vegetation quality supported beetle assemblages composed of significantly different communities. However, these differences were not consistent between all sites of different vegetation quality, suggesting that there may be additional ecological characteristics within the landscape responsible for shaping remnant beetle communities. No single, specific quality of remnant vegetation was optimal for supporting the most diverse assemblage of beetles, as different taxa responded independently. A range of remnants of differing qualities maintained across the landscape may provide the resources needed for the widest range of beetle taxa, by accommodating their varying habitat requirements.