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.

For partially harvested stands in the British Columbia interior, we present a new method for specifying regeneration stocking standards and a procedure for comparing achieved regeneration to the standard. Understory stocking is assessed in terms of the deviation from potential yield that the observed understory tree density represents. For a harvested area, the minimum stocking standard is stated as the maximum allowable mean deviation from potential. Deviation from potential is expressed on a relative (0–1) scale and predicted from overstory basal area and understory tree density. Because of a scarcity of calibration data, we undertook a crude, preliminary calibration of this relationship. As overstory basal area increases, the understory density required to achieve a given degree of understory stocking decreases. Issues pertaining to the stand management context and other approaches to regulating regeneration also are discussed. West. J. Appl. For. 20(1):5–12.

Variable retention (VR) refers to a strategy that is designed to retain biological legacies, such as large old trees, snags, and downed logs, at harvest to create and/or maintain structurally complex stands with a range of silvicultural systems. The retention system is a new silvicultural system (Forest Practices Code – Operational and Site Planning Regulations) designed for use under a VR strategy (Mitchell and Beese 2002). By retaining certain structural elements, habitat carrying capacity can be maintained and connectivity can be conserved over the landscape. The planning and implementation of VR is a complex process, with many potential risks that must be understood if one is to successfully achieve multiple management objectives. With the implementation of the retention system in coastal British Columbia, researchers have generated much information and learned many lessons. This Stand Establishment Decision Aid (SEDA) is intended to provide general guidance and points to consider when implementing the various structures (aggregated or dispersed) that are associated with the retention system in British Columbia's coastal forests. Additional information related to retention and variable retention can be found in the Resource and Reference list at the end of this document. It is important to note that the list provided in this reference section is not exhaustive and more information is available, but not necessarily cited. Reference material that is not available on-line can be ordered through libraries or the Queen's Printer at: http://www.qp.gov.bc.ca.