Brown rot in inner heartwood: why large logs support characteristics saproxylic beetle assemblages of conservation concernThis article is part of a larger document. View the larger document here.
It is not clear why large diameter logs generally host saproxylic beetle assemblages that are different from those of small diameter logs. In a study in Tasmanian wet eucalypt forest, two size-classes of Eucalyptus obliqua logs (>100cm and 30-60cm diameter) were destructively sampled to assess their beetle fauna and the associations of this fauna with decomposing wood. Ninety species were collected as adults from 42 logs; at least 19 species were also collected as larvae. The two log size-classes differed in beetle assemblage composition. These differences could be explained by the observation that certain beetle species were associated with specific successional phases of decomposing wood (rotten wood types). Those that were preferentially found in brown rotted heartwood, which was common in large logs, were rare or absent in small logs. This rotten wood type seems to be a relatively stable microhabitat and accordingly, the four most strongly associated species (in the genera Cossonus, Dryophthorus, Prostomis and Pycnomerus) seem likely to have low dispersal ability. Although relatively common in this habitat, each belongs to a genus whose European counterparts have undergone drastic range reductions. Our research highlights the importance of a level of landscape planning in Tasmanian forestry, which would maintain sufficient large diameter logs in the landscape over the long term.