Plot- and Sample-Size Trade-Offs for Tree Density and Basal Area Estimation Using Concentric Plot Reconstruction in an Uneven-Aged Abies × borisii-regis Forest

Forest-inventory precision depends jointly on plot size and sample size. Using 42 stem-mapped 1000 m2 plots in an uneven-aged hybrid fir (Abies × borisii-regis Mattf.) forest in Pertouli, Greece, we reconstructed 100–1000 m2 concentric plots at the same centers. RSE was calculated using a simple-random-sampling variance working approximation. At n=42, 300 m2 was the minimum acceptable plot size under an adopted ±10% practical agreement criterion relative to the 1000 m2 reference; the minimum remained 300 m2 at ±7.5% but increased to 400 m2 for basal area and 700 m2 for tree density at ±5%. Under a 5% RSE target, basal area met the target from 500 m2, whereas tree density met it at no acceptable size; both attributes met a 10% target from 300 m2. Controlled resampling and compartment-group analysis placed 95%–100% of group-by-size RSEs within same-sample-size resampling intervals. Pareto-efficient designs showed the sample-size–sampled-area trade-off. Holding total sampled area constant, more small plots reduced median RSE by 13%–23%. Designs requiring n>42 remain projections. Case-study plot-size values should not be transferred directly to other forest structures; the procedure provides a transferable way to define an acceptable plot-size range and evaluate sample-size and sampled-area trade-offs for a selected attribute and precision target.