Evaluation of inventories based on sample plots of variable size.

This paper deals with the estimation of per hectare values in forest inventories, based on sample plots of variable size. They are used in a national monitoring system in Slovakia and also, in a more complex form, as concentric circles in regional inventories and inventories of forest enterprises in Germany. A comprehensive theoretical analysis is completed by a simulation study in an artificial forest model in order to illustrate the results. In case of systematic samples on a lattice, as it is typical in forest inventory practice, the mean of the per hectare values of sample plots is shown to be a suitable estimator even if variable plot sizes are used. Instead, the ratio estimator can have a remarkable bias.