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.

European forests face increasing pressure from climate change and a growing number of invasive alien species. This study examines whether growth patterns and climate–growth relationships in pedunculate oak (Quercus robur L.) changed after the appearance of the oak lace bug (Corythucha arcuata; OLB) in the Spačva basin, Croatia. We analyzed 90 cores from 45 trees in young, middle-aged and old stands, comparing growth before and after 2013 (2000–2023). Structural change analysis identified a 2013 breakpoint in all stands, coinciding with the first regional detection of OLB. Growth trends declined significantly in young (p < 0.001) and middle-aged (p < 0.01) stands, but not in the old stand, and increased variability in tree-level slopes indicated heterogeneous individual responses. Declining mean interseries correlation (Rbar) and expressed population signal (EPS) suggested reduced growth synchrony. Positive correlations with precipitation and negative correlations with temperature strengthened in recent years, overlapping the period after OLB appearance. New earlywood signals emerged: a negative correlation with previous December precipitation and a positive correlation with previous October SPEI-3. As the breakpoint also follows the 2011–2012 drought and precedes the 2014 floods, the link to OLB remains correlative. We hypothesize that late-season drought, favoring OLB activity and limiting non-structural carbohydrate (NSC) replenishment, combined with winter waterlogging, may deplete NSC reserves and constrain growth the following year.