In 1995, to ensure forest practices were ecologically sustainable, the Clayoquot Sound Scientific Panel recommended replacing clearcuts with variable retention (Science Panel 1995). At the time, there was very limited experience with variable retention systems, including any information on the most effective retention systems, their influence on regeneration, or the extent to which they emulate natural disturbance patterns. There is a now a growing body of literature on the effects of variable retention on biodiversity. However, we still we do not have a good understanding of how variable retention systems influence regeneration performance or longterm sustained yield or how to adapt our silvicultural standards which are based on clearcuts to variable retention systems, such as multi-storied stocking standards. We have some information on regeneration performance in Douglas-fir forests in the Pacific Northwest but not for coastal forests, with shade tolerant species and different natural disturbance regimes. We also need quantitative measures of variable retention overstory related to the understory regeneration environment and how those conditions change over time, especially in coastal forests where wind throw damage is common. Further we need information on how the understory responds to variable retention over time, both for their biodiversity and cultural value, and competition with regeneration.
Variable retention is often categorized descriptively by level of retention (percent retained trees) and pattern (dispersed versus aggregate) (Franklin et al. 1997). However these qualitative descriptions do not necessarily quantify the physical regeneration environment nor are comparisons between different categories straightforward. Further, in coastal forests where wind is a major influence, the actual retention parameters may vary from the initial settings and not remain constant over the life of the stand due to wind damage. In a study of modelling windthrow risk of retained trees in variable retention systems in Clayoquot Sound, the authors found 16% of retained trees were wind-thrown (Scott and Mitchell 2005). Mean stand-level windthrow probability was 0.34 with a broad range from 0.17 to 0.74. Twenty percent retention appeared to be the critical threshold. When greater than 20% of the original stand was retained, few retained trees were wind-thrown, but below 20% half the retained trees were wind-thrown. Therefore wind damage can be a significant influence that is not accounted for in descriptive variables. Furthermore in west coast ecosystems, removal of overstory increases the vigour of the understory shrub complex which competes with understory trees, a factor which may also change over time. A further consideration in Clayoquot Sound is mandates associated with First Nations. The Clayoquot Sound Scientific Panel Report lists 27 recommendations associated with First Nations perspectives. These include undertaking research to enhance the effectiveness of sustainable ecosystem management. Iisaak is a First Nations-led forest company committed to practicing conservation-based forestry in Clayoquot Sound. They are certified by the Forest Stewardship Council (FSC). In order to address their mandate of upholding FSC certification principles, specifically appropriate monitoring and assessment activities to assess the condition of the forest and the maintenance of the ecological functions and integrity of the forest, they need data, such as generated from this study. First Nations in the Central and North Coast area (Great Bear Rainforest) LRMP processes have similar concerns. Companies working within the Great Bear Rainforest are exploring the possibility of FSC certification as well, especially the Heiltsuk 4 Nation. Further, many understory species are culturally important (Clayoquot Sound Scientific Panel Report 3, Appendix V) and we do not know how well these species persist in variable retentions settings.
Pearson, Audrey F., Warttig, Warren. 2009. SB3R POST-TREATMENT VEGETATION MEASUREMENTS OF STRUCTURE PLOTS ESTABLISHED IN 2003. Forest Investment Account (FIA) - Land Base Investment Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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