Coarse woody debris, biodiversity and management: a review with particular reference to Tasmanian wet eucalypt forests

Abstract

Summary This paper reviews the biodiversity conservation issues relating to management of coarse woody debris (CWD) in the wet eucalypt production forests of Tasmania, with particular emphasis on clearfell, burn and sow (CBS) silviculture and on fuelwood harvesting. CBS is the standard silvicultural system in these forests, while fuelwood harvesting, as currently proposed, would involve the recovery of a higher proportion of felled biomass than standard CBS, as well as some pre-existing CWD. Studies and practices from around the world are considered that have relevance to the temperate Australian forestry situation in general, and the Tasmanian situation in particular. The paper considers the ecological roles of CWD in natural forest ecosystems, emphasising its value as a key structural component and as habitat for biodiversity (especially invertebrates). Temporal continuity and spatial connectivity in supply of CWD, and presence of larger-diameter CWD, emerge as key factors determining community richness and composition. Whilst levels of CWD naturally fluctuate spatially and temporally in wet eucalypt forests, studies from northern temperate and boreal forests with similar dynamics demonstrate that, historically, management of native forests has tended to result in a gradual diminution of the CWD resource. Larger-diameter material is readily diminished through management, with potential consequences for dependent biodiversity. Suggested mitigation measures (landscape-level and coupe-level), to accommodate biodiversity concerns and avoid a long-term conservation management problem for forest managers in Tasmania, centre on two main concerns. One is the likelihood that current standard rotation lengths used in CBS are probably too short to allow for the recruitment of sufficient CWD to replace that which is lost through harvesting, regeneration burning and natural decomposition. The other concern is that fuelwood harvesting may significantly increase the impacts of CBS on biodiversity in general and on threatened species in particular.