RELATIONSHIP OF TARBUSH LEAF SURFACE SECONDARY CHEMISTRY TO LIVESTOCKHERBIVORY

Tarbush (Flourensia cernua DC.) is an abundant but generally unpalatab le shrub native to the Chihuahuan Desert. The objective of this study was to examine the leaf surface chemistry of tarbush in relation to de gree of use by ruminants. Mature tarbush leaves were collected on 2 si tes during 2 periods approximately 2 weeks apart from plants exhibitin g either high (>45%) or low (<10%) use when browsed by cattle, sheep, and goats confined to a small area (5 plants per use category for each site/period combination). A greater (P<0.05) concentration of epicuti cular wax was detected on the leaf surface of plants that were used to a lower degree (8.2 and 10.3% of the leaf dry matter for high-and low -use plants, respectively). Several leaf surface compounds were relate d to period, while site and degree of use were seldom related to indiv idual mono- and sesquiterpenes measured in this study. Camphene and 10 unidentified compounds differed between periods (P<0.10). Two unident ified compounds were related to site (P<0.10) and 2 others were relate d to use (P<0.10). In summary, individual leaf surface compounds on ta rbush do not appear to greatly affect degree of use of tarbush by live stock, but collectively (based on epicuticular wax data), these compou nds may influence the diet selected by browsing ruminants.