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Estimating Natural Regeneration and Yield in Pine-Dominated Stands Following Mountain Pine Beetle Attack Using SORTIE-ND and PrognosisBC in a Hybrid Modelling Approach
Sattler, Derek
The amount of timber affected by the current Mountain Pine Beetle (MPB) epidemic is beyond the industrial capacity to extract and process. Thus, a large portion of these stands will go unsalvaged, and much of the Province?s mid- to long-term timber supply will originate from these stands. This has placed considerable importance on the need to develop quantitative growth and yield models that capture the natural dynamics of MPB-affected stands. As a result, there is a need to develop quantitative growth and yield models that capture the natural dynamics of MPB-affected stands, beginning with the estimation of regeneration following attack. PrognosisBC is an empirical, tree-level, growth and yield model that has proven to be an effective forest management tool that can simulate a variety of silvicultural applications and can be used to provide operational estimates of growth and yield. Several approaches to estimating regeneration have been examined for use with PrognosisBC including using a set of probability models in partially cut stands (e.g., Boisvenue 1996) and using nearest neighbour imputation in partially cut and MPB-affected stands (e.g., Boisvenue 1996; Hassani et al. 2004; LeMay et al. 2006). However, the dynamics of natural regeneration recruitment and growth under MPB affected stands is markedly different than regeneration in thinned or partially cut stands, since dead trees remain standing for a long period of time, and remain on site once they fall. Ideally, regeneration estimations following MPB-attack should take into account the variable rates of mortality, snag decay and subsequent fall-down, and light transmission that are observed following MPB attack. SORTIE-ND is a process-based forest ecology model that simulates growth, mortality, recruitment, and resource availability. Model strengths lie in the spatially explicit light submodel and the ability to simulate natural regeneration. However, SORTIE-ND has had limited use in forest planning and forest operations. To this extent, regeneration estimates from SORTIE-ND coupled with projections using PrognosisBC could result in improved growth and yield projections in unsalvaged stands. Preliminary tests of SORTIE-ND to obtain regeneration indicated that this approach showed considerable promise (LeMay et al. 2006). In this project, we will use a hybrid modelling approach to estimate growth and yield following MPB-attack in pine-dominated forests of the central and southern interior of BC, by linking SORTIE-ND and PrognosisBC. To examine this hybrid modelling approach, first, the strengths of each of these two models will be examined in terms of providing accurate growth and yield estimates, from seedlings through to adult growth stages. Second, modifications to components of each model will be proposed and developed to strengthen the accuracy of regeneration and yield predictions for the application areas. In the third step, alternatives for linkages between the two models will be examined, including when the regeneration estimates are passed from SORTIE-ND to PrognosisBC. Data from the Cariboo-Chilcotin area gathered by Natural Resources Canada, and collected in the summer of 2006 from the Williams Lake area (FSP Project M07-5015), will be used in this project, along with data to be collected in summer 2007. These data will also be used to examine other approaches to estimate regeneration following MPB-attack (MMPI MPB Standard Contribution Agreement, PO # 8.35). A hybrid model that combines the strengths of the processed-based and empirically-based functions of SORTIE-ND and PrognosisBC would be a very useful tool for the projection of mid- to long-term yields. By focusing on the accurate prediction of natural regeneration, this study represents an important step in the development of a hybrid model that could be used to inform management decisions. For example, stands expected to have low natural regeneration densities following MPB attack could be a ...
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