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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.

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. 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 specializ...

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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.Keywords: silvicultural system, retention system, variable retention, ecosystem management La philosophie de l'aménagement écosystémique cherche un équilibre entre la protection des systèmes naturels et leur utilisation pour répondre aux demandes sociétales. Les objectifs des régimes sylvicoles énumérés dans les textes courants se concentrent sur la production soutenue de bois et sur le maintien de la qualité des stocks en croissance. Ces objectifs doivent être mis à jour dans le cas de situations où l'objectif général vise à maintenir les fonctions et la productivité de l'écosystème. Le « système à rétention variable » récemment adopté en Colombie-Britannique est un régime sylvicole conçu pour implanter une approche de « rétention variable » (rv) au niveau de la récolte. Avec la rv, des arbres sont préservés pour répondre aux objectifs écologiques comme le maintien de l'hétérogénéité structurale et la protection de l'héritage biologique. La contribution des arbres préservés au niveau du rendement ou de la régénération peut être faible ou même négative. Parmi les défis contenus dans l'implantation d'un régime de rétention, on retrouve l'ajustement des attentes en matière de rendement et des projections visées pour le peuplement qui tiennent compte de la santé et de la vigueur anticipée du peuplement dans l'avenir.Mot-clés: régime sylvicole, régime de rétention, rétention variable, aménagement écosystémique.

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 La conservation variable est une nouvelle approche aux systèmes de récolte et de sylviculture que des écologistes de la région du Nord-Ouest du Pacifique, en Amérique du Nord, ont mis au point pour atteindre un vaste ensemble d'objectifs pour l'aménagement forestier. La conservation variable reconnaît que des facteurs naturels de perturbation tels que le feu, le vent ou la maladie laissent presque toujours sur leur passage une structure résiduelle de la foret antérieure. Cette complexité structurelle joue un rôle important dans la fonction d'écosystème de la forêt et dans sa diversité biologique. On a défini un nouveau « système sylvicole de conservation » qui laisse subsister des arbres distribués sur les parterres de coupe. Ce système facilite la conservation des caractéristiques structurales des vieilles forêts telles que des arbres vivants et morts de tailles variables, des étages multiples du couvert et des débris ligneux grossiers. Chez Weyerhaeuser, le groupe « BC Coastal » appliquera cette approche à toute la récolte, dès 2003. Pour plus de 75 % de la récolte pratiquée dans la zone côtière de la Colombie-Britannique, cette société employait la conservation variable en 2001. Les lignes directrices que s'est données la compagnie décrivent, pour des groupes d'arbres et des arbres individuels, la quantité, le type et la répar-tition spatiale de la conservation. Un programme d'aménagement adaptatif permet de contrôler la quantité et le type de caractères structuraux conservés relativement à ceux de la forêt antérieure.

The Montane Alternative Silvicultural Systems (MASS) partnership was formed in 1992 to test new approaches to harvesting high-elevation old-growth forests of Vancouver Island, British Columbia. Uniform Shelterwood (SW), Green Tree Retention (GT) and Patch Cuttings (PC) were tested as alternatives to Clearcutting (CC). All systems were compared to an Old Growth (OG) control. Harvesting was completed in 1993. This paper summarizes the conclusions from the operational aspects of the study and reviews some early results from studies of the biological impacts. Harvesting costs to roadside were about 12% greater for the PC and GT and 49% greater for the SW. Cumulative losses to windthrow after three years were 25% in the GT and 5% in the SW. Site disturbance, soil compaction and rates of organic matter decomposition were low across all harvested treatments. Rates of organic matter decomposition and N mineralization on SW, GT and PC were intermediate between CC and OG. Nutrient loss in soil solution was reduced with partial harvesting but lack of available nitrogen is limiting the early growth of coniferous regeneration among all systems. During spring and summer, SW and CC treatments were generally cooler than PC or GT. Damage to understory vegetation and advanced conifer regeneration was least in the SW, which also provided the greatest amounts of seedfall among all harvested treatments. Key words: Abies amabilis, Tsuga heterophylla, Thuja plicata, Chamaecyparis nootkatensis, harvesting costs, site impacts, silvicultural systems, shelterwood

Stand-level retention is an important component of sustainable forest management which aims to balance ecological, social and economic objectives. Long-term retention of mature forest structures at the time of harvesting (variable retention) is intended to produce future forest stands that more closely resemble conditions that develop after natural disturbances, thereby maintaining greater diversity of habitats for a variety of organisms. Structure includes features such as live and dead trees representing multiple canopy layers, undisturbed understory vegetation and coarse woody debris. Over the past two decades, variable retention has become common on forest lands in the temperate rainforests of coastal British Columbia (BC) and has been applied to a lesser extent in inland forest types. Our review of studies in BC and in similar forest types in our region indicates that both aggregated and dispersed retention can contribute to biodiversity conservation by providing short-term 'life-boating' habitat for some species and by enhancing the structural characteristics of future stands. For example, greater abundance of species present in the pre-harvest forest have been documented for vegetation, birds, carabid beetles, gastropods, ectomycorrhizal fungi and soil fauna in retention cutblocks compared to clearcuts. There are, however, some negative consequences for timber production such as wind damage to retained trees and reduced growth rates of tree regeneration compared to clearcuts. The authors suggest an adaptive management approach for balancing competing objectives when faced with uncertainty. This includes monitoring the implementation and effectiveness of various strategies for achieving goals. Over two decades of experience applying variable retention harvesting to industrial-scale management of forest lands in BC suggests that it is possible to balance production of wood with biodiversity conservation.