Economic Impacts of Projecting Horizontal Angles to the Wrong Height When Conducting Point Sampling

摘要

Horizontal point sampling selects sample trees by projecting horizontal angles. In many inventories, angles are to be projected to dbh, or the diameter at 4.5 ft, but because cf user error, angles are often projected to heights other than breast height. Thus, errors are made as to which trees should be sampled, probabilities of sampling individual trees are incorrect, and the basal area estimate does not truly correspond to dbh. The objective of this study was to determine the potential economic impacts of projecting angles at heights other than breast height when breast height is the desired height. Projections for two planting densities (400 and 1,000 seedlings per acre) and two ages (20 and 30) were used to establish virtual plantations, and sampling was conducted using 10 and 20 basal area factor prisms by projecting horizontal angles to four heights, 4.5, 5.0, 5.5, and 6.0 ft. A taper equation was used to estimate changes in diameter along the stem. For the stand conditions examined in this study, incorrectly projecting angles to heights other than breast height reduced timber appraisals by as much as $190/ac. Across many acres and stands, this type of nonsampling error can result in serious errors in valuing stumpage.