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Abundance of critical wildlife habitat attributes in relation to forest management practices
Lewis, Douglas W.
Mitigating forest management impacts on a wide range of flora and fauna has become a common theme in forest management planning. Numerous studies have indicated that several habitat features that are often associated with unmanaged forests are critical for maintaining biodiversity and that these markedly diminish or disappear in stands managed with conventional clear-cutting of green timber or salvage operations. For example, several key mature forest attributes that are diminished during clearcut harvesting include large live trees, large declining or recently dead stems, and snags and downed wood representing a diversity of sizes and decay conditions (Franklin et al. 2000). These structural elements are critical to many species and although they are significantly reduced or in some cases virtually eliminated by conventional clear-cut harvesting systems, a suite of alternative practices are available that will help maintain significant components of these features in managed stands (Franklin et al. 1997, Franklin et al. 2000, Franklin et al. 2002, Hartley 2002, Lindenmayer and Franklin 1997, Lindenmayer and Franklin 2002, Serrouya and D?Eon 2003, Vanha-Majamaa and Jalonen 2002). Such features are used or required by approximately 35-40% of the terrestrial forest-dwelling vertebrates (Bunnell et al. 2004) and many other biota. In general, these attributes are likely to diminish in abundance on areas that have been clear-cut harvested or where future harvesting entries will disrupt the development of old forest conditions. However, retaining components of mature forest in the cutblock is one widely accepted way to diminish forest management impacts on a wide range of biota. A discussion of the application and benefits of retaining forest structure in operational situations is presented by Zielke et al. (2003). Some practices that will help protect and maintain mature forest attributes in the short- and mid-term include: a) Leaving single tree and aggregated Wildlife Tree Retention areas well-distributed across the cutblock. b) Complementing the retention in Wildlife Tree Retention and Riparian Reserve Zones with Partial Retention harvesting. Partial retention harvesting is an application of variable retention harvesting (Mitchell and Beese 2002) and maintains a component of the mature green tree and snag structure of the original stand, while allowing for the removal of up to as much as 75% of the timber. Partial Retention harvesting will retain a component of the mature stand structure that will help provide habitat and refugia for the many plants and animals that do not require extensive forest interior conditions. It will help provide cover for animals attempting to cross the clearcut salvage harvest opening, provide hiding cover for species such as large ungulates and carnivores that frequently use early seral habitat, but avoid large openings without cover, and provide a seed source or refugium from which plants or animals from the original mature stand can colonize the newly developing stand. This is especially important for organisms such as arboreal lichens that are more likely to colonize new sites through fragments vs. propagules. c) Retaining as much downed wood, well dispersed across the site, as is feasible. Examples include non-merchantable snags and green wood, especially large diameter material, either as standing trees or cut and left at the stump vs. hauled to cull piles. This can be enhanced with with non-merchantable piece sizes and low quality material (e.g. pulp) wherever feasible. Scattered small piles of downed wood (e.g. 10-20m3) complement dispersed downed wood by providing subnivian (the relatively open, crystalline layer that forms between the ground surface and snowpack) access points for species such as marten. Although there is considerable literature linking stand structures such as large live trees and snags and downed wood to biodiversity, and concensus that alternative silvicultura ...
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