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    Author(s): Martin W. RitchieJianwei Zhang
    Date: 2018
    Source: Gen. Tech. Rep. PSW-GTR-259. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (10.0 MB)


    OP-Yield is a Microsoft Excel™ spreadsheet with 14 specified user inputs to derive custom yield estimates using the original Oliver and Powers (1978) functions as the foundation. It presents yields for ponderosa pine (Pinus ponderosa Lawson & C. Lawson) plantations in northern California. The basic model forms for dominantand subdominant-height (Powers and Oliver 1978), height-diameter relationships, and stand density index-driven mortality (Reineke 1933) were derived from the original publication in the first implementation of this model. However, after reviewing trends, the height-diameter relationships were revised by refitting the model with more current data. Thus, results do not match the original.

    In the original Oliver and Powers (1978) model, many controlling parameters were fixed, significantly limiting the ability to interpolate. These fixed parameters also have relegated the original model obsolete in some respects. However, in OPYield several fixed parameters in the original system are allowed to flex. The other major difference between OP-Yield and the original presentation is the derivation of cubic-foot volume by age and site. In Oliver and Powers (1978), final yield is derived from a complex polynomial smoothing function of site and age. In OP-Yield, volume is instead an expression of these preliminary calculations. In this sense, OPYield volumes are internally consistent. With these changes, yields differ between the two systems, even for situations in which the settings in OP-Yield match the assumptions of Oliver and Powers (1978). In general, volume and basal area are substantially less in OP-Yield than in forecasts by Powers and Oliver (1978).

    Op-Yield Microsoft Excel™ spreadsheet v1.00.4 (5.8 MB)

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    Ritchie, Martin W.; Zhang, Jianwei. 2018. OP-Yield Version 1.00 user's guide. Gen. Tech. Rep. PSW-GTR-259. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 26 p.


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    Ponderosa pine, yield, growth model, density management

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