Estimating edge effects on ground-dwelling beetles at clearfelled non-riparian stand edges in Tasmanian wet eucalypt forest

Abstract

Edge effects potentially have negative consequences for biodiversity in logging areas. In Tasmanian wet eucalypt forest, ground-dwelling beetle assemblages responded to habitat edges between mature unlogged forest and young regeneration following clearfelling. Transects of pitfall traps extended 100 m into unlogged forest and 10 m into the felled area firebreaks at four study sites (4 sites × 3 transects × 8 traps/transect = 96 traps). The depth of edge influence extended between 10 m and 25 m into mature forest, and the beetle assemblage was estimated to be 95% similar to interior forest at approximately 22 m from the edge. The species composition of beetles changed gradually with distance from the edge, but for practical purposes we distinguished three zones of edge response: mature forest interior extending ≥22 m into unlogged forest, firebreak habitat at the edge of the coupe that extends 1 m into unlogged forest, and an edge-affected mature forest zone in between. Individual species known to be characteristic of mature and young forest were of greatest indicator value in mature forest interior and firebreak habitat, respectively. Choleva TFIC sp 01 (Leiodidae), Decilaus nigronotatus, D. lateralis and D. striatus (all Curculionidae) were identified as indicator species characteristic of mature forest interior. No species were found to be characteristic of the habitat edges. These results are relevant to current management practices in Tasmanian wet eucalypt forest, in particular to the efficacy of linear reserve networks. One hundred metre wide wildlife habitat strips, when bounded by recently harvested forest, are estimated to contain a little over 50% of interior habitat not compromised by edge effects. Small patches of forest (<1 ha) retained in variable retention harvesting are predicted to contain little or no uncompromised interior habitat for ground-dwelling beetles.