Location: Range Management Research
Title: Is differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration? Authors
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2013
Publication Date: February 16, 2014
Repository URL: http://handle.nal.usda.gov/10113/58717
Citation: Estell, R.E., Utsumi, S.A., Cibils, A.F., Anderson, D.M. 2014. Is differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration? Journal of Chemical Ecology. 40:285-293. Interpretive Summary: Encroachment of woody plant species such as one-seed juniper into rangelands is a concern for livestock producers and ecologists alike. A study was conducted to determine the role of plant chemicals (terpenes) on juniper browsing by sheep and goats. Smaller saplings had lower terpene concentrations, especially during the summer. Browsing intensity was inversely related to terpene concentration in small saplings. Consequently, targeted browsing of one-seed juniper by small ruminants should be most effective on small saplings during the summer.
Technical Abstract: We examined the relationship between volatile plant secondary metabolite concentrations and Juniperus monosperma herbivory by small ruminants. Two groups of animals (10 goats or 5 goats plus 4 sheep) browsed 16 paddocks (20 x 30 m) containing one-seed juniper for six days during two seasons. Juniper leaves were sampled from 311 saplings on the same day they were browsed. Saplings were categorized by size (short [< 0.5 m], medium [0.5-1.0 m] or tall [> 1.0 m]) and browsing intensity (light [< 33%], moderate [33-66%] or heavy [> 66%]). Juniper bark was also collected from 12 saplings during spring. Total estimated terpenoid concentrations in leaves and bark were 18.3 ± 0.3 and 8.9 ± 0.8 mg/g, respectively, and the dominant terpene in both tissues was a-pinene (11.1 ± 0.2 and 7.6 ± 0.7 mg/g, respectively). Total terpenoid concentration was greater (P < 0.001) in spring than summer (20.6 ± 0.5 vs. 16.7 ± 0.3 mg/g, respectively) and lower (P < 0.001) in short saplings than medium or tall saplings (16.5 ± 0.6 vs. 19.8 ± 0.4 and 19.5 ± 0.4 mg/g, respectively). Total concentration also differed (P < 0.001) among the three defoliation categories (16.1 ± 0.4, 18.7 ± 0.5, and 21.2 ± 0.6 mg/g for heavy, moderate, and light, respectively). The smallest subset of terpenes able to discriminate (P < 0.001) between heavy and light browsing intensity categories included eight compounds ([E]-ß-farnesene, bornyl acetate, '-eudesmol, endo-fenchyl acetate, '-cadinene, a-pinene, cis-piperitol, and cis-p-menth-2-en-1-ol).