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Modelling the development of Coastal BC stands: an individual tree model linked to a variable retention microclimate model
Rathbun, Leah
Plans for 2007-2008 No major deviations from the original project plan are envisaged. A PhD student is in place working on height, diameter, mortality and taper equations. We have made substantive progress modelling mortality (natural and managed) and height and diameter growth (natural stands) estimation functions. We have improved leaf area index estimates and are working on a new hemlock taper and branch data base. The PSP and variable retention (VR) database are in place and the FORGE model (our modeling/simulation framework) has a mixture of new and existing parameters in place (see Hann et al., 2003) as well as improved microclimate equations. (In order to get the ITDI model functional we coded in equations presented in Hann et. al 2003 in 2007-2008: these will be replaced by local equations as the actual models are completed). In 2008-2009 we will focus on dbh and height increment for managed stands (thinned, fertilized) having worked on natural stands in 2007-2008. We will investigate the use of nonlinear mixed models on error structure in the modelling framework (see Weiskittel et al. 2007 for the general approach that we will use). This will improve the parameter estimates and reduce residual model variance. We will develop taper equations further using ITLP data and continue to add to the taper data base (an in-kind project). We will update all tree growth models in FORGE and continue model testing. The VR modifiers will also be further developed using new data collected in 2007-2008 and theoretical relationships. In 2007-2008 we developed some prototype natural and planted regeneration models (growing seedlings to 1.3m to pass onto the overstory model) these will continue to be improved on using new data (collected here and elsewhere) in 2008-2009. ITLP will directly fund the measurements of several VR edge and experimental sites (see below for a description of edge and experimental). These data are all important in ?locally? calibrating the model to BC Coastal condition. We request some funds to continue some hemlock branch and leaf area field work in 2008-2009 using the approach outlined in Smith (1992) (see Methods) . General 3- year Project Description (unless noted) Generally, the proposed model is designed to meet the following requirements for Coastal BC: ?take an existing inventory and grow each tree forward.?take a given stand condition (for instance 900 fir, site index 30, age 30 years) and grow it forward.?take a regeneration description (i.e. plant 1000 fir, natural regeneration of 300 hemlock, 10% group retention) and grow it forward.?incorporate a mechanism for modelling the impacts of variable retention on the above?output should be for any specified year (i.e. not just 5 year periods).The data sets includes: ?PSP database (~2500 PSPs): includes mainly trees greater than breast height, 1.3m.?Regeneration data: collected from seedlings at planting to breast height in clearcut retention stands (~100 stands). ?A variable retention growth database of 10 experimental sites and 19 gradient analysis sites (Beese et al. 2005) that contributes regeneration data up to 8 years after planting. See also: for a description of the edge and experimental data?Taper data: over 240 destructively sectioned trees, continued collection as an in-kind contribution. ?Leaf area index and branch data base and estimating equations for Douglas-fir previously developed. Existing models: no ITDI yield validated model exists for the BC Coast, existing models have weak regeneration components with rudimentary linkage to variable retention (i.e. they are largely data free). The following model components will be developed over the course of the 3 year project: 1.Height growth; 2.diameter growth; 3.mortality; 4.modifier effects of fertilizer and thinning, on 1,2 and 3; 5.regeneration model: clearcut data and variable retention data; 6.taper equation; 7.modifier e ...
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