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University of Nevada, Las Vegas (2019)

Landscape Scale : Inter- and Intraspecific Variation in Plant Interactions along a Stress Gradient in the Sheep Range of Nevada

Dowell Jordan

Titre : Landscape Scale : Inter- and Intraspecific Variation in Plant Interactions along a Stress Gradient in the Sheep Range of Nevada

Auteur : Dowell Jordan

Université de soutenance : University of Nevada, Las Vegas

Grade : Master of Science (MS) 2019

Résumé
Impending threats to shrubland ecosystems, posed by climate change, necessitate niche modeling efforts to project vegetation range shifts. However, efforts often remain unguided by individual-scale interspecific plant interactions. The stress gradient hypothesis posits that facilitation should increase in areas of high abiotic stress, only if the individuals are able to ameliorate the surrounding area via functional traits. The Sheep Range of Nevada was used to assess the role of functional traits as predictors of plant association. Larrea tridentata, Coleogyne ramosissima, and Artemisia nova were selected as shrubs with variable life history strategies and ranges in order to identify general patterns between canopy level traits concerning morphology and physiology to intensity of interactions. Over the observed gradient there was a predominance of competition, defined by reduced undershrub abundance in comparison to adjacent spaces. However, data suggest that interaction may not be driven specifically by macroclimate but by microclimate modulating traits, as observed net effects of facilitation or competition were more greatly impacted by composites of traits, as opposed to singular traits. Composite traits that parsed canopy morphology and physiology, defining plants by canopy size, leaf nutritional value, and resource-use efficiency were significant predictors of relative interaction intensity (RII) (Adj. R2 = 0.49—0.7, p < 0.01). δ15N, was the only singular trait positively associated with RII when accounting for other aspects of climate and plant physiology and morphology (Adj. R2 = 0.64, p < 0.001). Contrary to the stress gradient hypothesis, climate what not a significant predictor of RII when accounting for plant morphology and physiology. Over time as the macroclimate continues to fluctuate, above and beyond ameliorative ability, these facilitative interactions may shift to competition. As such, further identification of patterns of association and trait characteristics will be imperative to provide suitable assessments of potential community dynamics shifts.

Mots clés  : climate change ; Functional traits ; Nurse plant ; Plant ecology ; relative interaction

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