Relationships between site index and ecological variables of trembling poplar forests (Populus tremula L.) in Türkiye

This study was carried out to identify relationships between site index (dominant height at a reference age) and ecological variables of trembling poplar forests in Türkiye. Samples were collected from 78 plots differing in elevation, aspect, inclination, slope position, and site class. Physiographic factors of the sample plots were recorded, soil samples were collected from different predefined layers from soil pits, and bedrock samples were collected for identification. From three trees at the stand top height, the tree closest to the arithmetic mean height was felled, and its height and age were determined. Physical and chemical characteristics of the soil samples were analysed. Relationships of the soil properties, physiographic factors, and climate with site index were assessed with correlation, stepwise regression, and regression tree methods. Significant relationships were found between site index at 30 years and elevation from the physiographic factors; the maximum temperature and the number of snowy days of the coldest month from the climate characteristics; fine earth, silt, and pH from the percentage values of soil properties at different depths; and fine earth, silt, and clay from the soil characteristics aggregated on pedon level. The height growth of trembling poplar was 11.8% according to stepwise regression analysis and 18% according to the regression tree method. The models obtained in the current study might help evaluate the potential of sites regarding the growth of trembling poplar.