RANDOM-PARAMETER HEIGHT AGE MODELS WHEN STAND PARAMETERS AND STAND AGE ARE CORRELATED/

Height/age curves of dominant trees in a stand can be predicted using models containing random stand and tree parameters. If the population mean curve is estimated from the data where stand-specific parameters are correlated with stand age (e.g., because old stands are growing on poor sites), this correlation may cause biased estimates. The same bi as problem occurs in traditional site index methods. It is shown how o rdinary least squares estimates of tree specific parameters can be use d for computing unbiased estimates of the population mean parameters a nd for estimating the relationship between stand parameters and stand age. The application of the estimated model several years after the da ta collection time is problematic because it should be known how the p opulation changes over time.