Date of Award:

5-2022

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Committee Chair(s)

Andrew Kulmatiski

Committee

Andrew Kulmatiski

Committee

Karen H. Beard

Committee

Peter B. Adler

Committee

Kyle A. Palmquist

Committee

D. Richard Cutler

Abstract

As the atmosphere warms, precipitation events become larger, but less frequent. Such increases in precipitation intensity are expected regardless of changes in total annual precipitation. Despite strong evidence for increases in precipitation intensity, disagreement exists regarding how these changes will impact plants, and studies are lacking in many types of ecosystems. This dissertation addresses how increased precipitation intensity affects soil water availability, and how plants respond to any such changes. I address this question in the context of big sagebrush ecosystems and dryland winter wheat agriculture, which are both environments that can be sensitive to changes in water availability. Results from two field experiments (Chapters 2 & 3) and modelling (Chapter 4) indicate that fewer larger precipitation events cause water to be ‘pushed’ deeper into the ground. In sagebrush ecosystems this benefitted shrubs, because they tend to have deeper roots and could preferentially access the deeper soil water. The model simulations indicate that these positive effects on shrub growth should be expected in dry climates, but not in wetter climates where larger precipitation events caused more water to be lost to deep drainage. By comparison, increased precipitation intensity had little effect on more shallowly rooted herbaceous plants in sagebrush ecosystems. Similarly, production of winter wheat was not affected by increased precipitation intensity, potentially because this crop matures early in the growing season, while changes in soil moisture were most apparent only later in the summer. My research shows that responses to increased precipitation intensity are likely to differ between plant types and that larger precipitation events may contribute to patterns of increasing dominance of woody plants that can be observed globally. More broadly, these results stress the importance of accounting for climatic variability when forecasting ecological responses to climate change.

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