Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081156

    An experimental study of variable-retention harvest methods on forest birds
Project lead: Chan-McLeod, Ann (University of British Columbia)
Author: Chan-McLeod, Ann
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Variable-retention (VR) harvesting is a promising silvicultural technique for maintaining biodiversity while allowing timber extraction (Lindenmayer and Franklin 2002). However, many questions remain regarding its effectiveness in sustaining biodiversity, and in how it should be implemented to maximize its effectiveness (Lindenmayer and Franklin 2002). The amounts, types, and spatial arrangement of both live and dead residual structures vary widely from one form of variable-retention harvesting to another. In dispersed retention, single residual structures are distributed uniformly over the harvested area, but in aggregated retention, residual structures are concentrated in small intact areas of forest within the harvested matrix. There are many tradeoffs between each approach, with for example, dispersed retention accommodating territorial behavior in animals but lacking the niches provided by the intact soil, understory and overstory layer in aggregated retention. The variability of structural retention harvesting, coupled with its short implementation history, mean that the key issues of what structure to retain, how much to retain, and how to distribute the structures across space have received limited empirical assessment despite its widespread application.
The overall objective of this study is to evaluate the effects of dispersion pattern, retention level, patch size, and size of opening on avian communities, using an experimental approach that specifically addresses the knowledge gaps and limitations of the existing database on VR effects, and that exploit existing experimental sites and data. The study treatments and study sites for this research are part of a series of replicated, experimental harvesting blocks that test different types, amounts and spatial patterns of retention. These Variable Retention Adaptive Management (VRAM) experimental sites were previously the foundation of Weyerhaeuser’s Adaptive Management program; this program is being continued by Western Forest Products Inc with the change in company ownership. Each VRAM site was installed with random allocation of treatments, and was chosen to be as uniform as possible in timber type, site series and topographic features.
This proposal seeks to exploit the colossal investment in funding and effort that has gone into establishing these sites and in the availability of baseline data for various vertebrate and invertebrate taxa. The effectiveness of VR methods in sustaining biodiversity may best be addressed at these experimental sites with new research on avian response because: 1) Birds are by far the most species rich group of vertebrates, and represent the full spectrum of wildlife habitat requirements; 2) Birds are significant biodiversity indicators of other taxonomic groups, including woody plants and aquatic herpetofauna (Kati et al. 2004); 3) There are tight and well-defined relationships between bird communities and stand-level structure and habitat; and 4) Many existing studies have shown that birds do respond positively to green tree retention - residual tree patches such as those found in VR cutblocks retained avian species that would normally disappear after clearcut logging and that are characteristically associated with old-growth forests (Beese and Bryant 1999; Schieck et al. 2000; Tittler et al. 2001). Moreover, there is evidence to indicate that different forms of variable-retention harvesting, created by varying such factors as retention level, will differ in their effectiveness in sustaining biodiversity (e.g., Tittler et al. 2001, Chan-McLeod and Vernier 2004,Stuart-Smith et al. 2006). Existing data on VR effects on birds are, however, limited by various study constraints including: 1) the evaluation, to date, of only a small subset of dispersion patterns and retention levels; 2) generally snap-shot assessments of very short time windows following VR harvesting; and 3) rare simultaneous analyses of multiple VR factors such as dispersion pattern and retention level. Analyses of the concurrent effects of dispersion pattern and retention level were attempted by Chan-McLeod and Bunnell (2003) in a retrospective study of operational VR cutblocks, but these analyses were limited by confounding in the harvest treatments, since operational VR cutblocks typically have low retention levels when trees are retained as single scattered trees, but high retention levels when trees are retained in groups or patches. Schieck et al. (2000) simultaneously analysed residual tree density and degree of clumping in trees, but their study was conducted at the plot level, and therefore, results could not be extrapolated to avian response at the cutblock level. The experimental harvests in this proposal explicitly address this limitation by allowing concurrent assessment of multiple harvest factors. The evaluation of population trends over the long-term is facilitated by the incorporation of the proposed research into an industrial adaptive management program with long-term monitoring. Currently, published information on VR effects are generally limited to less than 2 year time windows (e.g., Tittler et al. 2001, Schieck et al. 2000, Chan-McLeod and Bunnell 2003). Stuart and Smith et al. (2006) assessed the widest time window following post-harvest (up to 45 years) but their study lacked immediate post-harvest responses (< 5 years post-treatment) nor was there concurrent analyses of retention level and dispersion pattern. The project findings from this research will directly inform and guide operational forestry as the research forms part of Western Forest Product’s Adaptive Management Program, and provide practical guidelines for achieving the most effective methods for sustaining biodiversity under variable retention harvesting. Harvest treatments comprise operationally feasible tree patch sizes, dispersion pattern, and gap sizes that can be viably implemented if they prove promising for biodiversity conservation.
Literature Cited • Beese & Bryant 1999. For. Ecol. and Manage. 115:231-242. • Chan-McLeod & Bunnell 2003. Report to Weyerhaeuser, Coastal Group. • Kati et al. 2004. Cons Biol 18:667-675. • Lindenmayer & Franklin 2002. Island Press, Wash. D,C. • Schieck et al. 2000. For. Ecol. and Manage. 126:239-254. • Tittler et al. 2001. Ecol. Applic. 11:1656-1666. • Stuart-Smith et al. 2006. For. Ecol. and Manage. 231:1-17.
Related projects:  FSP_Y092156FSP_Y103156


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Updated August 16, 2010 

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