Ecoregion-based height-diameter models for Crimean pine

Abstract

Generalized height (h)–diameter (d) models were developed for Crimean pine stands in the Kastamonu Regional Directorate of Forestry, northwestern Turkey. Nine generalized h-d models were fitted and evaluated based on data set consisting of 2697 h-d measurements obtained from 274 sample plots located in three ecoregions of the studied region. The best results were obtained by modified Richards h-d model accounting for the 93% of the total variance in height–diameter relationship. It is a known fact that h-d relationship can vary in ecological conditions, especially for regions with large areas and various ecological conditions such as Kastamonu. To investigate the differences of height–diameter relationship among the ecoregions located in Kastamonu region, nonlinear extra sum of squares method was performed. The test results showed that there were significant differences, especially between coastal and the inland ecoregions. When compared to reduced model with the same set of parameters for the whole region, full model with a different set of parameters for each ecoregion achieved better accuracy in estimating tree height. Besides, applying h-d model fitted for the coastal ecoregion to the others, or vice versa, could lead under- or over-estimates of tree heights by about 1.8%.