Distance-limited perpendicular distance sampling for coarse woody debris: Theory and field results.

Abstract Coarse woody debris (CWD) has been identified as an important component in many forest ecosystem processes. Perpendicular distance sampling (PDS) is one of the several efficient new methods that have been proposed for CWD inventory. One drawback of PDS is that the maximum search distance can be very large, especially if CWD diameters are large or the volume factor chosen is small. Here, we propose a modified method, which we call distance-limited PDS, that addresses this limitation. We describe the field procedures, develop new a new estimator, and provide a proof of unbiasedness of that estimator. The new method is compared with line intersect sampling (LIS) and PDS in a field trial in the northeastern United States. The results of the field trial show that this new method requires as little as the sampling effort of LIS in order to achieve comparable variance of the estimates