Measurement Errors from Successive Inventories on Concentric Circular Field Plots and Their Impact on Volume and Volume Increment in Uneven-Aged Silver Fir Stands

Forest measurements are essential for monitoring stand dynamics and long-term trends. Errors in tree measurement can seriously affect the outcomes of a forest inventory. This study investigates measurement errors from successive measurements on permanent concentric circular plots based on data from 74 plots in Dinaric uneven-aged mixed fir–beech stands. Tree data errors were detected and corrected. Diameter increment was calculated as a difference in DBH from two successive inventories, and linear regression models were developed based on original and corrected data. Measurement errors were identified in 2.57% of trees, some having a substantial impact on tree volume. Volume discrepancies between original and corrected data were generally minor, where 93.2% of plots in the first and 70.3% in the second inventory required no corrections and volume differences in the overall levels were negligible and statistically non-significant: 0.30 m3/ha in the first inventory (p = 0.550) and 0.05 m3/ha in the second (p = 0.974). Although diameter increment models with original and corrected data differed significantly, model choice resulted in minimal impact on volume increment. Since omitting erroneous measurement data would lead to volume underestimation, data correction is preferable. However, when modeling tree increment, excluding incorrect or doubtful data remains a practical and acceptable approach.