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University of Nevada, Reno (2011)

Climatic influences on sagebrush establishment in Arid Rangelands : Applications for rangeland rehabilitation

Hourihan, Erin V.

Titre : Climatic influences on sagebrush establishment in Arid Rangelands : Applications for rangeland rehabilitation

Auteur : Hourihan, Erin V.

Université de soutenance : University of Nevada, Reno

Grade : Master of Science (MS) 2011

Sagebrush-dominated ecosystems are threatened by altered fire regimes, invasive species, infrastructure development, conversion to cropland, and encroachment by woody species. The economic and ecological significance of sagebrush makes it very important to develop successful strategies for re-establishing it on abandoned mine sites and degraded rangelands. The transition of intact sagebrush ecosystems to ecologically damaged rangelands is especially problematic because it degrades wildlife habitat, reduced biodiversity and potentially alters ecosystem function (Davies and Svejcar 2008). Here I assess the relationship between sagebrush recruitment and climatic events. Stem sections were collected from the following species : Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle & Young), black sagebrush (Artemisia nova A. Nelson), low sagebrush (Artemisia arbuscula Nutt. ssp. arbuscula), and Lahontan sagebrush (Artemisia arbuscula ssp. longicaulis Winward & McArthur). Stem sections were collected to provide information on the age of the stand, and I directly dated the years of successful recruitment through annual growth-ring analysis. Linking annual growth-rings of sagebrush to climate identifies climatic patterns responsible for recruiting new sagebrush cohorts. In Nevada, primary applications of this research include rehabilitation of mined lands, wildfire areas and habitat monitoring of sagebrush obligate wildlife species. Recruitment of sagebrush cohorts was significantly correlated with climate variables, although the relationship varied by species or sub-specific identity. Recruitment in sagebrush populations occurred in pulses throughout Nevada and stand ages were significantly different (P<.001) among species and subspecies. Total precipitation the year prior to recruitment and the year following recruitment were reasonably good predictors of seedling establishment. Patterns in seedling establishment showed strong patterns in timing of recruitment pulses for individual species or subspecies, even though study sites were not located geographically close to one another.The most interesting finding of this research was the significance of global climatic patterns. Monthly Pacific Decadal Oscillation (PDO) index variables were correlated with seedling recruitment in all species studied. This relationship was significant (á=.05) for low sagebrush at and Wyoming big sagebrush at each study site. July PDO was the most significant variable for low sagebrush at the Willow Creek Ridge site (R2=0.1058, P<0.0026) and the Montana Mountain Site (R2=0.2188, P<0.0023). April PDO was the most significant variable for Wyoming big sagebrush at the Antelope Valley site (R2= 0.1459, P<0.0071) and the Santa Rosa site (R2= 0.1435, P<0.0248). In general the shift from cool to warm phase of the PDO corresponded with increased sagebrush cohort recruitment (Figure 13, 14, 15 & 16). These results suggest that timing restoration efforts with the larger climatic environment may result in increased success.

Mots clés  : arid rangelands Artemisia precipitation pulse recruitment sagebrush seedling recruitment

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