A Comparison of Twig-length and Browsed-twig Methods of Determining Browse Utilization

Abstract

Utilization of shrubs has been determined by several techniques, two of which are: (1) measuring twig lengths before and after use then calculating the percentage and (2) estimating the percentage of browsed twigs. Estimates were checked for accuracy by actually counting the number of browsed and unbrowsed twigs and then calculating percentages. The two methods were compared on a big game winter range in southcentral Utah to evaluate the agreement among utilization estimates, consistency among individual observers, and efficiency. Estimating the percentage of browsed twigs or calculating percentages from counts of browsed and unbrowsed twigs provided higher utilization values than measuring twig lengths. Disadvantages of estimating percentages of browsed twigs include the introduction of individual bias when estimates are made and lack of sensitivity in accurately determining percentage utilization under heavy use. By contrast, calculating percentages of utilization from twig length measurements provided equal sensitivity throughout the 0 to 100% range. Twig measurement data were more consistent among observers than estimates. Measuring twig lengths required about four times as many man-hours as estimating percentages of browsed twigs or counting twig numbers.