The majority of the world's forests are used for multiple purposes, which often include the potentially conflicting goals of timber production and bi

Summary: Industrial forestry typically leads to a simplified forest structure and altered species composition. Retention of trees at harvest was introduced about 25 years ago to mitigate negative impacts on biodiversity, mainly from clearcutting, and is now widely practiced in boreal and temperate regions. Despite numerous studies on response of flora and fauna to retention, no comprehensive review has summarized its effects on biodiversity in comparison to clearcuts as well as un‐harvested forests. Using a systematic review protocol, we completed a meta‐analysis of 78 studies including 944 comparisons of biodiversity between retention cuts and either clearcuts or un‐harvested forests, with the main objective of assessing whether retention forestry helps, at least in the short term, to moderate the negative effects of clearcutting on flora and fauna. Retention cuts supported higher richness and a greater abundance of forest species than clearcuts as well as higher richness and abundance of open‐habitat species than un‐harvested forests. For all species taken together (i.e. forest species, open‐habitat species, generalist species and unclassified species), richness was higher in retention cuts than in clearcuts. Retention cuts had negative impacts on some species compared to un‐harvested forest, indicating that certain forest‐interior species may not survive in retention cuts. Similarly, retention cuts were less suitable for some open‐habitat species compared with clearcuts. Positive effects of retention cuts on richness of forest species increased with proportion of retained trees and time since harvest, but there were not enough data to analyse possible threshold effects, that is, levels at which effects on biodiversity diminish. Spatial arrangement of the trees (aggregated vs. dispersed) had no effect on either forest species or open‐habitat species, although limited data may have hindered our capacity to identify responses. Results for different comparisons were largely consistent among taxonomic groups for forest and open‐habitat species, respectively. Synthesis and applications. Our meta‐analysis provides support for wider use of retention forestry since it moderates negative harvesting impacts on biodiversity. Hence, it is a promising approach for integrating biodiversity conservation and production forestry, although identifying optimal solutions between these two goals may need further attention. Nevertheless, retention forestry will not substitute for conservation actions targeting certain highly specialized species associated with forest‐interior or open‐habitat conditions.

Approximately 85% of the global forest estate is neither formally protected nor in areas dedicated to intensive wood production (e.g., plantations). Given the spatial extent of unprotected forests, finding management approaches that will sustain their multiple environmental, economic, and cultural values and prevent their conversion to other uses is imperative. The major global challenge of native forest management is further demonstrated by ongoing steep declines in forest biodiversity and carbon stocks. Here, we suggest that an essential part of such management—supplementing the protection of large reserves and sensitive areas within forest landscapes (e.g., aquatic features)—is the adoption of the retention approach in forests where logging occurs. This ecological approach to harvesting provides for permanent retention of important selected structures (e.g., trees and decayed logs) to provide for continuity of ecosystem structure, function, and species composition in the postharvest forest. The retention approach supports the integration of environmental, economic, and cultural values and is broadly applicable to tropical, temperate, and boreal forests, adaptable to different management objectives, and appropriate in different societal settings. The widespread adoption of the retention approach would be one of the most significant changes in management practice since the onset of modern high‐yield forestry.

The philosophy of ecosystem management seeks a balance between protecting natural systems and using them to meet societal demands. The objectives of silvicultural systems listed in standard texts focus on the sustained production of timber and maintenance of quality growing stock. These objectives need updating for situations where the broader goal is to sustain ecosystem function and productivity. The "retention system" recently adopted in British Columbia is a silvicultural system designed to implement the "variable retention" (VR) approach to harvesting. With VR, trees are retained to meet ecological objectives such as maintaining structural heterogeneity and protecting biological legacies. The contribution of retained trees to yield or regeneration may be low or even negative. Among the challenges in implementing the retention system is the adjustment of yield expectations and target stand projections to account for the expected health and vigour of the future stand. Key words: silvicultural system, retention system, variable retention, ecosystem management

Variable retention is a new approach to harvesting and silvicultural systems that was developed by ecologists in the Pacific Northwest region of North America to address a wide array of forest management goals. Variable retention recognizes that natural disturbances, such as fire, wind or disease, nearly always leave some standing structure from the original forest. This structural complexity plays an important role in forest ecosystem function and biological diversity. A new "retention silvicultural system" was defined that leaves trees distributed throughout harvested areas. This system facilitates retention of structural features of old-growth forests, such as live and dead trees of varying sizes, multiple canopy layers, and coarse woody debris. Weyerhaeuser's British Columbia Coastal Group will use the variable retention approach for all harvesting by 2003. More than 75% of the company's coastal harvesting in British Columbia used variable retention in 2001. Company guidelines describe the amount, type, and spatial distribution of retention for groups and individual trees. An adaptive management program is monitoring the amount and type of structural attributes retained in relation to the original forest. Key words: old-growth forests, variable retention, silvicultural systems, biodiversity, landscape zoning