Is the Concentric Plot Design Reliable for Estimating Structural Parameters of Forest Stands?

Monitoring forest stands using sampling techniques offers a valuable alternative to conventional forest condition assessment methods in Central Europe. While these designs are optimized for assessing production parameters, their effectiveness for structural characteristics remains unclear. This study evaluates various plot designs to determine their reliability in estimating structural diversity indices, including the Gini index, Artenprofile index, and Shannon index. We compared ten fixed-radius (FR) sampling designs (plot sizes: 50–1250 m2) and a concentric circle (CC) design (500 m2) employed at the Mendel University Forest Enterprise (Křtiny, Czech Republic). The CC design proved adequate for assessing production parameters and structural diversity indices like Artenprofile and Shannon. However, it showed significant limitations for the Gini index (p < 0.01), due to a smaller number of sampled trees. For the Gini index, fixed-radius plots of at least 150 m2, with 200 m2 being the most cost-effective size, provided the most reliable estimates. Interestingly, the CC design may also be less suitable for production parameters, where smaller fixed-radius plots (50 m2) were more effective, requiring fewer total samples despite the need for more plots.