Photographic standards for estimating comparative yield in arid rangelands.

Abstract

When the conventional comparative yield method was tested in arid rangelands with a diversity of range types, species and structure, it gave rise to large differences between operators' estimates of yield, which were not easily reduced by calibration. As well, the procedure was too time consuming for a monitoring system. To improve the efficiency of yield estimation, we tested a modified version which substituted a folio of photographs for the selection and assessment of reference standards and calibration quadrats. The differences between operators' estimates were still large, but could be relatively easily reduced by periodic calibration because operators used the technique more consistently than the conventional method. We suggest that the reliability of estimates would be improved with extra training, a wider choice of photostandards and the use of a single operator. The procedure is rapid and easy to use, and we recommend its use in combination with the dry-weight-rank technique for species composition. A program is available which enables the collection and analysis of data from both methods in the field, using a hand-