CORRELATED OBSERVER ERRORS AND THEIR EFFECTS ON SURVEY ESTIMATES OF NEEDLE-LEAF LOSS

In Europe, crown transparency is one of the most important variables a ssessed for monitoring forest conditions. Though there are very strict international guidelines and intensive training programs for the eval uation of needle-leaf loss, there still exists a subjective component in the evaluation. This subjective component in the observation proces s can lead to a nonsampling error that can greatly reduce the precisio n of estimates of average needle-leaf loss. In this paper, methods for quantifying the potential loss in precision are presented and applied to data from the Swiss National Forest Health Monitoring Program.