Accuracy and suitability of several stand sampling methods in riparian zones

Abstract

Stand structure in headwater riparian areas of western Oregon is highly variable making quantification of structural attributes within these stands difficult. A reliable sampling design is important to characterize and monitor changes in stand structure over time. This study examined sixteen alternatives for sampling live conifers and six alternatives for sampling hardwoods and snags. Each sampling alternative was replicated 500 times on a 72 meter square stem map at eight headwater stream locations in western Oregon. A variety of plot sizes and shapes were considered at two sampling intensities of 10 % and 20 % of the stand area. Applied to live conifers, the performance of the alternatives were assessed with respect to estimation of trees per hectare, basal area per hectare, and height to diameter ratio using root mean square error, average mean deviation and percent bias as criteria. Performance with respect to snags and hardwoods was similar. In general, rectangular strip designs oriented perpendicular to the stream outperformed circular, radial plots, and variable plots.