UC Riverside

Mountain ecosystems in western North America are highly sensitive to climate change and are warming faster than the global average. Found at the tops of these mountains, the alpine tundra ecosystem is especially threatened due to its fragmented distribution (so called “sky islands”), limited area, and the impossibility of alpine species moving to higher elevations. As a result, alpine sky islands are considered a “sentinel system” for detecting the biological impacts of climate change, and rapid changes in alpine biodiversity are expected in the coming decades. In this dissertation, I explore how climate change is driving shifts in alpine plant biodiversity patterns (chapter 1), how species interactions structure current patterns of alpine biodiversity (chapter 2), and how variation in climatic conditions may affect the relationship between biodiversity and ecosystem function (chapter 3). To investigate these questions, I employ an observational study of regional plant biodiversity across a 12-year period, a neighbor removal experiment paired with spatial point pattern analysis, and structural equation modeling using data from the Niwot Ridge Long Term Ecological Research Program, respectively. I find evidence that: 1) alpine biodiversity patterns are shifting, notably towards species possessing traits which enable drought tolerance; 2) species interactions and species spatial patterns are largely governed by traits related to plant size like leaf area and height, though the manner in which these traits relate to species coexistence mechanisms changes across alpine community types; and 3) the alpine biodiversity-ecosystem function relationship is also best predicted size-related traits; however, the ability of these traits to predict ecosystem function varies strongly depending on the amount of winter precipitation. Overall, my dissertation highlights that alpine biodiversity change is detectable over relatively short time periods, and that these changes are likely to have important implications for species interactions and the biodiversity-ecosystem function relationship.