Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071269

    Range of Natural Variation in Structural Attributes of Young Stands: Refining Current Indicators
Project lead: Lloyd, Ruth
Contributing Authors: Lloyd, Ruth A.; Price, Karen; Burton, Philip J.; Daust, Dave
Imprint: [BC] :, 2007
Subject: Forest Investment Account (FIA), Natural Disturbances, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Structural attributes of old forests, including downed wood, large live trees, dead and decaying trees, and patches of shrubby vegetation, provide critical habitats for a variety of mammals, birds, invertebrates, plants and lichens (Bunnell et al. 2003, Price and Hochachka 2001, Schoonmaker and McKee 1988). Most natural disturbances leave some structural attributes in the newly-regenerating stand (Hansen et al. 1991, Franklin et al. 2000). Legislation (e.g., Forest and Range Practices Act) and land-use plans (e.g., Sustainable Resource Management Plans, Landscape Unit Plans, Forest Stewardship Plans) prescribe retention of wildlife tree patches — with a variety of structural features — in young managed stands. However, high uncertainty about the threshold amount of structure needed to maintain biodiversity currently limits the usefulness of wildlife tree patches as an indicator of sustainability. A risk assessment undertaken by the Babine Watershed Monitoring Trust ( highlighted resolution of this uncertainty as a top priority. Currently, many managers are setting targets for stand-level retention with little or no science to support those targets. For example, in areas with high mountain pine beetle infestation, the target for stand structure retention has been doubled from the provisions in provincial policy to reflect the widely held belief that disturbance by mountain pine beetles would increase the level of naturally occurring stand structure (MSRM 2003). However, the question remains: increase retention by how much? What portion of harvested stands should be included within wildlife tree patches to minimise the impacts of forestry on biodiversity? Two complementary lines of research address this question: first, studies can examine the response of selected species to different amounts of structure, providing good answers for some species but in a “piece-meal” approach; second, research determining the range of natural variability (RONV) of structural attributes for particular ecosystems provides a more holistic, coarse-filter, approach. The latter approach assumes that organisms have adapted to RONV, and likely provides a less accurate answer for a given species. It can, however, provide broadly applicable answers that can be implemented relatively quickly. Analogous to efforts to maintain biodiversity over the landscape, an efficient, combined, approach defines coarse-filter thresholds based on RONV, and modifies thresholds for species of particular interest based on fine-filter research. Much work has been undertaken to define the RONV for the frequency and size of disturbance (Bergeron et al. 2002, DeLong 2002), but little has described the RONV for stand-level attributes remaining after disturbance (Bergeron et al. 1999, Franklin et al. 2000; but see related work in Prince George area by DeLong and Kessler 2000). The proposed study will define likely RONV for structural attributes within common ecosystems of the Northern Interior Region. Our research question specifically asks “Within the northwestern SBS and ESSF subzones, what is the range of natural variation in post-disturbance stand structure among different disturbance agents and in different ecosystems”. This question addresses FSP Sustainability Program Theme 3: Sustainable forest management indicators, targets and monitoring systems; Topic 3.2: Indicator targets and thresholds of sustainability; and Priority b: Determining the likely range of natural variation for coarse- through fine-filter indicators as a means to assess potential targets and management thresholds. The study area is the SBS and ESSF of the Northern Interior Forest Region, with field work occurring in and around the Babine River Watershed of the Skeena-Stikine Forest District. This watershed is the focus of a series of special management requirements, in which forestry activities are expected to protect high-value salmon, grizzly bear, biodiversity and wilderness resources (see The research question is of particular importance to monitoring the land-use objectives in the Babine. In 2004 – 2005, a multi-stakeholder group (representing the interests of forest industry, three government agencies, private tourism operators and local residents) developed a framework for prioritising monitoring projects. This group then established an independent trust (Babine Watershed Monitoring Trust: BWMT) that is responsible for implementing monitoring in the Babine Watershed, guided by the framework. This stand structure project is one of the top priorities identified in the BWMT’s analyses and is included for funding in their Annual Monitoring Plan. The results of this research project will be used immediately by the Babine Watershed Monitoring Trust to inform analyses of the risk and uncertainty associated with various management activities. In their initial analyses, risk to biodiversity is assessed, in part, by comparing structural retention in managed stands to RONV. Problematically, RONV of structural attributes is poorly known. The data will also be used to test a disturbance classification system that considers the amount and dispersion of overstory removal, understory removal and forest floor disturbance (Roberts 2004). Such a system should provide a more complete characterisation of disturbance, help in the design of management techniques that better mimic natural processes, and aid our understanding of the impact and implications of existing management practices.


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Updated August 16, 2010 

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