Seeking a balance between forestry and biodiversity - the role of variable retention silviculture. Insights from western USA and Canada

achieve improved biodiversity and social outcomes compared to clearcutting and other traditional silvicultural systems. VR was initially developed in the Pacific Northwest (PNW) of USA and Canada, where it is applied in a broad variety of forest types, ages and land tenures. VR has recently been implemented in wet old-growth forests in Tasmania, and there is scope for broader implementation in both Tasmania and mainland Australia. Hence, insights from the PNW about operational experience, research, adaptive management, and efforts to improve relationships between timber industry and environmental groups are of broad relevance to forest management in Australia. This report covers three main topics. Chapter 2 presents the results from surveys of twelve organizations that are currently implementing VR across western USA and Canada. These surveys explored motivations for using VR, variation in implementation, adaptive management and monitoring, and perceived success of the system. Chapter 3 of the report discusses research and formalized adaptive management programs relating to improving conservation outcomes from silvicultural practices. This includes descriptions of some of the large silvicultural trials investigating biodiversity and silvicultural outcomes of VR and clearcutting. Two emerging areas of research are discussed: the importance of early-seral forests for biodiversity, and the role of ‘forest influence’ in facilitating recolonisation of harvested areas by biodiversity from nearby mature forest. Chapter 4 provides examples of successful collaborations that have settled long-term conflicts between timber industry and environmental groups, resulting in improved conservation outcomes and continued timber production. The development and implementation of VR in the PNW has been an excellent example of adaptive management. Although the desire for improved social acceptability was often a primary driver for using VR along with the desire for improved ecological outcomes, organizations clearly embraced the ecological objectives of the system. There was a lot of variability in VR implementation across the region. The system was used in a wide variety of forest types, including old-growth, second and third-growth forests; and a variety of land tenures including those managed by industrial companies on both public and private lands, State governments, small private ownerships and First Nations people. Most organizations used one or more of the three main harvesting patterns: aggregated retention where uncut forest is left in groups, dispersed retention where scattered trees are retained, and mixed retention which combines the previous two approaches at the one site. Aggregated retention and mixed retention were most widely used. This related to a combination of operational, social and ecological factors. Research trials are showing that aggregates are able to maintain a broader variety of species than are dispersed trees, although some species are advantaged by the more uniform distribution of trees with dispersed retention. Windthrow monitoring has shown that with the exception of some wind-firm species, windthrow is reduced with aggregated retention. Large aggregates are less prone to windthrow than small ones. Organizations using VR were adapting their practices in response to operational experience and the results of research and monitoring. Those organizations with direct links to research trials appeared to be making the most informed changes. Good training programs, strong leadership and organizational cultures supportive of ecologically sustainable forestry practices were important to success. Using VR had generally achieved the social and ecological objectives, and organizations were planning on continued implementation. However there was uncertainty over long-term ecological outcomes, emphasising the need for long-term biodiversity research.