Productivity modeling of black pine afforestation areas according to site factors in Sultan mountains (Afyonkarahisar) region

This study was conducted to determine the relationships between the productivity of black pine (Pinus nigra) afforestation sites and certain climatic and soil properties in the Sultandağı region, located within the borders of Afyonkarahisar province. A total of 36 sample plots were established for data collection. Site productivity (site index), soil, and climatic characteristics were identified within these plots. To model the productivity of afforestation areas, age and height measurements were performed on selected plus black pine (Pinus nigra) trees located in 36 sample plots established at different elevations and isolated from human disturbances. In each sample plot, a soil pit was excavated, and soil samples were collected from the identified horizons. In the laboratory, several physical and chemical properties of the soil samples were determined. In addition to soil variables, climatic parameters were also recorded at the study area scale for use in the modeling phase. For modeling the productivity of black pine afforestation sites, multiple regression analysis and regression tree methods were applied. According to the multiple regression analysis results, the variables Bio12 and 30–60 cm clay content contributed positively to the model, whereas Bio1 and 0–30 cm clay content contributed negatively. Based on the regression tree technique, the resulting tree model was structured with the variables Bio1, Bio12, and 0–30 cm silt content. In terms of determination coefficients (R² values), stepwise multiple regression analysis was found to be more explanatory than the regression tree method. The results obtained from this study are expected to provide valuable contributions to plantation activities, ecological research, and conservation planning—both in the afforestation areas of the Sultandağı region of Afyonkarahisar and at the national and global scales.