Diameter-Length,-Weight Relations for Blackbrush [Coleogyne ramosissima] Branches

Abstract

Regression was used to relate branch diameter to branch length (r = 0.85) and weight (# = 0.94) for blackbrush plants in southwestern Utah. These regression equations were subsequently used to estimate blackbrush utilization by domestic goats in a browsing study. The diameter-length equation compared favorably with before-and-after measurements for accuracy and greatly reduced man-hour costs in determining utilization. Estimates of utilization based on the diameter-weight equation were less than estimates based on the before-and-after approach or the diameter-length equation; the diameter-weight equation accounted for leaves and thus provided a more accurate estimate of utilization. Blackbrush (Coleogyne ramosissima) is a shrub occurring in nearly monospecific stands on millions of hectares of rangeland in the southwestern United States. The terminal twigs of blackbrush branches tend to die back for several centimeters from the tip resulting in a spinescent growth form. Death of terminal buds suppresses apical dominance and allows lateral twig development, which has a pronounced effect on compacting the plants. As a result of the compacted, spinescent growth form, the accessibility and palatability of blackbrush forage is low for cattle. Domestic goats were used to modify the growth form of blackbrush in southwestern Utah (Provenza 1977). Winter goat browsing removed spinescent material from blackbrush plants, which