Assessment of Coarse Woody Debris

Abstract

In this paper, different probability sampling methods for assessing coarse woody debris (CWD) are compared. The methods are circular plot sampling, strip surveying, line intersect sampling, and transect relascope sampling. The two latter methods are suited primarily for the assessment of CWD on the ground.

While the first three methods should be well known, the transect relascope method is new. It can be considered a combination of line intersect sampling and relascope sampling. A wide angle relascope is used along survey lines and all downed logs that fill the angle of the instrument are included in the sample.

The methods were compared with respect to their cost-efficiency for estimating the total length and the total volume of CWD on the ground in forest compartments. MonteCarlo simulation was used for the purpose. Regarding volume estimation, strip surveying was found to be an efficient method in most compartments. Concerning the estimation of the total length of logs, transect relascope sampling was found to be efficient. It should, however, be stressed that the knowledge of the performance of the transect relascope in the field is limited. It is likely that measurement errors make the method less accurate than is indicated in this theoretical study.

Assessing the total length of CWD is cheaper than assessing the total volume of CWD. In case line intersect or transect relascope sampling is used, the length can be estimated by only counting the logs included in the sample. The usefulness of the total length of logs as an indicator of habitat conditions can, however, be questioned. Still, if logs are classified into different dimension classes, a description of this kind should not be too different from using the total volume of logs.