RELATIONSHIP OF TARBUSH LEAF SURFACE TERPENE PROFILE WITH LIVESTOCK HERBIVORY

Tarbush (Flourensia cernua DC.) is a Chihuahuan Desert shrub with a re sinous leaf surface containing terpenes that may affect livestock herb ivory. Cattle, sheep, and goats were densely stocked in paddocks conta ining tarbush in two consecutive years for six to nine days and defoli ation of 160 plants was recorded daily. Plants were categorized as exh ibiting high or low defoliation. Leaves were collected from these plan ts the third year fbr chemical analysis. A selection procedure was use d to generate two variable sets closely related to defoliation categor y. One set contained 14 variables (dry matter, ash, alpha-pinene, sabi nene, 3-carene, p-cymene, limonene, camphor, borneol, cis-jasmone, bet a-caryophyllene, alpha-humulene, ledene, and flourensadiol) and the ot her set contained 14 unidentified compounds. When subjected to multiva riate analysis, each group distinguished between the two defoliation c ategories (P < 0.001 and P < 0.0019 for known and unknown variable set s, respectively). These data support the hypothesis that leaf surface chemistry of individual tarbush plants is related to extent of defolia tion by livestock.