Diameter Increment Estimations of Open-Grown Stone Pine (Pinus pinea L.) Trees in Urban Parks in Istanbul, Türkiye

Open-grown trees in cities can improve environmental conditions by providing sustainable ecosystem services. Reliable data are necessary for assessing the functions of urban trees. The diameter at breast height (DBH), diameter increment, and annual ring measurements are the main parameters in the development of reliable models. To model periodic mean diameter increments calculated for different time periods (5, 10, 15, 20, and 25 years), a total of 43 open-grown stone pines (Pinus pinea L.) of different diameter classes were sampled in several urban parks in Istanbul, Türkiye. The DBH was measured, and increment cores were extracted from each tree at 1.30 m stem height using an increment borer. Tree age at breast height was determined by counting annual rings, and periodic mean diameter increments were calculated for different periods based on the measured tree-ring widths. The periodic mean increments of different periods were related to the inside-bark diameter at breast height and tree age. Since there was no significant relationship between tree age and periodic mean increments for each period’s length, as shown in the correlation analysis, models used to estimate the periodic mean increments of inside-bark DBH were developed using the least squares regression and quantile regression (QR) techniques. As the period length increased, the estimation success of the diameter increment models increased while the mean absolute percentage error (MAE) values decreased from 40 to 32%. The best model was the one used for the last 25-year period with the quantile value q = 0.50 which estimated the diameter increment with an RMSE = 1.391 mm/year and MAE = 32.27%.