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Abstract:
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Gap dynamics define the forest structure and natural successional processes on Vancouver Island (Lertzman et al. 1996), with Douglas-fir as the dominate, pioneer species and western hemlock and western redcedar as late-successional species often aggregated within gaps (Getzin et al. 2006). In juvenile stages of growth, shade intolerant species, such as Douglas-fir, utilize photosynthate to height growth rather than diameter growth (Chen and Klinka 2003), outcompeting western hemlock, a shade-tolerant species. These differences in growth patterns due to levels of shade-tolerance are further complicated by species composition. In this area, Douglas-fir grows above shade-intolerant western hemlock and it has been suggested that resources between the two species are used in complement (Erickson et al. 2009). Management practices in this area have included clearcutting, thinning, variable retention harvesting, and fertilization. The complexity of stand structure is further supported by diversity within treatments applied as thinning intensity, timing of thinnings, and number of thinning. Forest management planning requires the development of growth models as a component of stand development under varying silvicultural treatments (Palahi et al. 2003). To model growth increment under different silvicultural treatments found on Vancouver Island, a flexible increment model is required. The Box and Lucas model is based on the metabolic processes governing tree growth, which unlike other models, allows for direct interpretation and can result in accurate predictions. The Box and Lucas model was fitted for three main species: Douglas-fir, western hemlock, and western redcedar using a random coefficients modeling (parameter prediction) approach to determine parameters. To estimate the impacts of thinning and fertilization on diameter increment growth, a two-step additive approach was tested, in that diameter increment was modified due to fertilization, and then again due to thinning.
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