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Growth Model Users Group Growth Model Run-off II

Growth Model Users Group Growth Model Run-off II. History. GMRO I was conducted in 2002. The objective was to test the effect of growth model and user combinations on the projections of three predominately Douglas-fir stands.

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Growth Model Users Group Growth Model Run-off II

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  1. Growth Model Users GroupGrowth Model Run-off II

  2. History • GMRO I was conducted in 2002. • The objective was to test the effect of growth model and user combinations on the projections of three predominately Douglas-fir stands. • 7 models: CRYPTOS, DFSIM, FPS, FVS, ORGANON, SPS, and TADAM were tested, using 11 different versions. • 16 users contributed results.

  3. History • Some observations on the results: • “Region” effects are very large. FVS in particular can more than double volume between regions. • There was significant variation among users running the same model and version. • All models maintain a remarkably consistent relationship between stand height and volume (Eichorn’s Rule). • CRYPTOS (an out-of-growing-region model) projections were very similar to northern growth models.

  4. GMRO II • A proposal to examine common Douglas-fir growth model performance for the following scenarios: • Commercial thinning • Nitrogen fertilization • Thinning and fertilization

  5. Why Do This? • GMUG Poll indicated that most users rely on their growth models for both biologic and economic evaluation of treatment effects. • There is a long history of thinning studies in Douglas-fir and the effects of thinning are thought to be understood. • Yet, thinning effects in many models require modifiers to component growth equations, indicating that the empirical models are not sufficient as-is to predict post-thinning growth. • N fertilization also has a long history in the PNW. Region-wide response has been well documented in the literature. • However, analyses of response at the tree level (required to incorporate fertilization into tree list models) has not been well documented. The translation of increased nutrient availability to growth in tree dimensions is not well modeled empirically. • Both of these treatments leave a lot of room for the modeler to define response relationships. Their decisions may have important impacts on growth & yield.

  6. Questions: • What models should be tested? • How many stands should we project (variation over site quality, density)? • What growth reporting intervals should we use and how long should the projection run? • Who should run the projections (users, modelers, both)? • What should be compared (volume, height, Dq, basal area, crown ratio, trees per acre, diameter distributions)?

  7. Questions: • Treatments: • Thinning: • What d/D? • What thinning intensity (single, multiple)? • Should we specify the thinned trees or leave it to the person running the model? • Fertilization: • What dosage (200 lbs N/acre)? • How many applications? • What re-application interval?

  8. Incentive?

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