Establishing Browse Utilization from Twig Diameters

Abstract

Measurement of twig lengths before and after browsing and measurement of twig diameter after browsing are two techniques to estimate utilization. The two techniques were compared for bitterbrush (Purshia tridentata) and cliffrose (Cowania stansburiana). Utilization percentages determined from the two approaches were highly correlated. However, regression equations were not required to estimate utilization from the diameter measurements alone. Correction factors were obtained by subtracting the twig tip diameter of unbrowsed twigs from diameter at the browsed tip and from basal diameter; then dividing the corrected browsed-tip diameter by the corrected basal diameter and multiplying by 100. By using the correction factor, valid estimates of percentage utilization were obtained. The numerical value for twig-tip diameter can be obtained from measuring twig tips of a representative number of unbrowsed twigs. Estimating utilization from twig diameter has two major advantages: (1) accurate estimates of utilization can be reconstructed from postbrowsing measurement alone and (2) making a single annual visit to the rangeland can represent a considerable time saving.