Two-phase approaches to point and transect relascope sampling of downed logs

Point relascope sampling and transect relascope sampling were recently prop osed as methods for the inventory of downed coarse woody debris. By only co unting logs with a relascope device, the total length squared (with point r elascope sampling) or the total length (with transect relascope sampling) o f downed logs in an area can be estimated. For estimates of other variables , such as volume, additional measurements on the sampled logs are required. In this article, two-phase approaches to the methods are presented that ma kes use of the estimates from fast counts of logs as auxiliary data. The pr esented approaches serve two purposes: (i) to improve the efficiency of the methods and (ii) to avoid the bias that is likely to occur if careful chec ks of whether or not doubtful logs should be counted are neglected. Each tw o-phase design was compared with a single-phase design in terms of the stan dard error obtained for a given inventory cost. The two-phase designs decre ased the standard errors with ca. 17-18% for points and 10-15% for lines. I ncluding subjective judgements as additional auxiliary variables further de creased the standard errors in the line case but not in the point case. In the former case, the improvement in comparison with the single-phase design was 17-23%.