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Stability and density management in Douglas-fir plantations

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  • In their recent Canadian Journal of Forest Research Comment 368 article, Wilson and Oliver (2000) developed an equation for predicting the average ratio of height to diameter at breast height for the largest 250 trees/ha (H/DL250) in unthinned stands as a function of initial density and dominant height of the stand. They then compared predictions from this equation to predictions of H/DL250 from (i) the southwestern Oregon version of the ORGANON (Hann et al. 1997) growth model (SWO-ORGANON), (ii) the Stand Management Cooperative version of ORGANON (SMC-ORGANON), and (iii) the Pacific Northwest variant of the Forest Vegetation Simulator. They found that predictions of H/DL250 from both versions of ORGANON were “…considerably higher (beyond 15 m of height)…” (p. 914) than predictions from their equation. They concluded that, “Users should critically evaluate growth model predictions of partial distribution statistics, such as H/DL250, before they are employed” (p. 917). As a forest modeler with 25 years of experience, I certainly agree with this warning to users of growth models, and as the primary architect and developer of ORGANON, I am always concerned when users, such as the authors, raise concerns about the predictive ability of the model. Unfortunately, the authors’ description of the data sets used in their analysis was so vague (i.e., “…a representative plantation at a variety of initial Douglas-fir densities;” p. 913) that it was impossible to reproduce and examine their results directly. This problem was resolved by contacting the senior author who promptly supplied the missing detailed description of the data and copies of the initial tree lists used to make the ORGANON runs. A close examination of these data and of the methods and results that were reported by the authors indicates that there are at least three problems with their application of the two ORGANON versions that seriously cloud the veracity of their findings.
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  • David W. Hann. 2001. Stability and density management in Douglas-fir plantations. Can. J. For. Res. 31: 367–368.
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  • 31
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  • 2
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