Comparison of combinations of sighting devices and target objects for establishing circular plots in the field

Many aspects of ecological research require measurement of characteristics within plots. Often, the time spent establishing plots is small relative to the time spent collecting and recording data. However, some studies require larger numbers of plots, where the time spent establishing the plot is consequential to the field effort. In open habitats, circular plots are easily established using a rope or tape. In tall or dense vegetation, however, considerable time can be spent ensuring that measures of plot radii are straight-line measurements. To rapidly establish fixed-radius plots in the field, common forest survey techniques can be used with a target object calibrated to the desired size of the plot. Although mentioned in past publications, the accuracy of establishing plots with these methods has not been evaluated. We tested the accuracy and precision in establishing fixed-radius plots using different sighting device/target object combinations. A laser rangefinder aimed at 10.2-cm PVC pipe was most accurate and precise, but expensive, and required careful handling. Wedge prisms used with a 10.2-cm PVC pipe or cylinder were accurate, precise, inexpensive, and easy to use.