Submitted to: Wildland Shrub Symposium Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 2, 1995
Publication Date: N/A
Technical Abstract: Tarbush (Flourensia cernua DC.) Is a generally unpalatable shrub native to the Chihuahuan Desert. Tarbush epicuticular wax concentration has previously been linked to degree of use by livestock. In 1989 and 1990, cattle, sheep, and goats were densely stocked in tarbush-containing paddocks for 6 to 9 days. Degree of use of 20 plants in each paddock (8 paddocks, 2 sites) was recorded daily. In 1991, leaves were collected fro these plants (n=160) during the same stage of maturity. Leaf surface compounds were extracted with ethanol and mono- and sesquiterpenes were analyzed using gas chromatography/ion trap mass spectrometry. Our objective was to examine whether degree of tarbush use during the high-density study was related to chemistry of the same plants the following year. Plants were separated into 3 categories (Category 1: >50% use at period midpoint; Category 2: <50% use at midpoint but >50% use at period end; Category 3: <50% use at period end). Multivariate analysis is being used to examine relationships of individual plant use with dry matter, ash, epicuticular wax, and several mono- and sesquiterpenes. Preliminary evaluation suggests chemical subgroup variables in 1991 were related to degree of herbivory in 1989 and 1990. We will determine which individual compounds contribute to these differences. Of the 120 plants with use data for both years 66 plants in a given use category for 1989 were in the same category in 1990 and 38 plants were in a higher category. Only 15 plants fell to a lower use category, and only 1 plant dropped from Category 1 to 3. Degree of use was reasonably consistent for individual plants across years, suggesting that if induction occurred, it was short term. Leaf surface chemistry appears to be related to degree of use of individual tarbush plants by livestock.