Continuous cover forestry: Which sampling method should be used to ensure sustainable management?

The transformation of even-aged forests into continuous cover forests to improve resilience and to promote biodiversity in Central Europe necessitates a re-evaluation of forest sampling designs. This study examines the precision and accuracy of two widely used terrestrial sampling methods, namely Angle Count Sampling and Fixed Area Plot Sampling. By simulating multiple samples in typical well-established Plenter forests in Switzerland, we analyse the error components and variabilities of the different methods for three key stand parameters: stem number per hectare, basal area per hectare and annual basal area increment per hectare. Our results suggest that, depending on the parameter of interest, the standard deviation, and the acceptable margin of error, the number of needed sample plots exhibits a large variation. Since the key stand parameters for ensuring sustainability in Plenter forests are the stem number by diameter at breast height class and the basal area increment, our results suggest that a Fixed Area Plot with 300 m2 circles is the best compromise between cost efficiency and precision for the sampled Plenter forest data. Alternatively, a Fixed Area Plot of 500 m2 or a combined Angle Count Sampling method with a basal area factor of 4 m2/ha and a 200 m2 Fixed Area Plot may be considered.