Juniper sapling regrowth following targeted grazing treatments in relation to terpenoid concentration

TitleJuniper sapling regrowth following targeted grazing treatments in relation to terpenoid concentration
Publication TypeConference Paper
Year of Publication2019
AuthorsAlmalki Y.M, Cibils A, Estell RE, Stricklan D., Utsumi S.A, Fernald A.G
Conference Name72nd Society for Range Management International Meeting
Date Published02/2019
PublisherSociety for Range Management Meeting Abstracts
Conference LocationMinneapolis, Minnesota
ARIS Log Number358983

Chemically defended woody plants are expected to grow at slower rates compared to less-well defended counterparts. The objective of our study was to determine whether regrowth of browsed one seed juniper saplings (Juniperus monosperma) was related to initial terpenoid concentrations. Targeted grazing with small ruminants was applied on sixteen 10 x 30 m sapling-infested rangeland plots at NMSU’s Corona Range and Livestock Research Center in the summer of 2006 (n=8) and spring of 2007 (n=8). Immediately after grazing, foliage of approximately 10 saplings in each plot was harvested and subsequently analyzed using gas chromatography/mass spectrometry. In 2017, we returned to the plots to measure sapling survival and regrowth. We hypothesized that sapling regrowth rate would be inversely related to terpenoid concentration measured in 2006/07. We used linear regression to explore this hypothesis using PROC REG in SAS 9.4. Plot averages were used in two separate regression analyses (summer and spring). Crown height of saplings increased 20.1 ± 1.4 cm and 19.9 ± 2.2 cm, and terpenoid concentration was 0.30 ± 0.01 mg/gDM and 0.26 ± 0.01 mg/gDM in spring and summer plots, respectively. Terpenoid concentration explained 52% of the variation in sapling regrowth in spring plots (ß = -88.2; P=0.04) and 81% of the variation in sapling regrowth in summer plots (ß = -227.6; P<0.01). As predicted, we found an inverse relationship between initial terpenoid concentration and one seed juniper sapling regrowth 10y after applying targeted grazing treatments with small ruminants. Since sheep and goats preferentially browse saplings with low terpenoid levels, our results suggest that heavily browsed saplings that survive are likely to exhibit the highest regrowth rates after treatment.