Modeling Diameter Distributions of Mixed-Oak Stands In Northwestern Turkey

ABSTRACT Background: Diameter distribution models are one of the most important components of growth and yield models. Diameter distribution models, based on the Weibull function, were developed for even-aged mixed-oak stands (Turkey oak, Sessile oak, and Hungarian oak) in northwestern Turkey. Two modeling methods were considered. Weibull parameters were recovered from either equation predicting Dq and Dvar (method of moments) or equations predicting Dq and D 90 (hybrid method). For each modeling method, three estimation methods were considered: (a) Least Squares method, (b) CDF Regression method in which regression coefficients were estimated separately for each species, and (c) CDF Regression method in which regression coefficients were simultaneously estimated for all species. Results: Results indicated that the hybrid method coupled with the CDF Regression estimation method yield best results in this study. Similar results were obtained when the regression coefficients were estimated either separately for each species or simultaneously for all species. Conclusion: The proposed models enable one to predict diameter distribution of a given mixed-oak species stand in northwestern Turkey, using limited stand information. These models are useful tools for the inventory and management of mixed-oak stands.