Causes and Consequences of Plant Responses to Environmental Change over Physiological, Ecological, and Evolutionary Time

Assessing how environmental change affects plants is increasingly important as terrestrial ecologists attempt to predict future patterns from current processes. However, this challenge is complicated because plant communities can respond to environmental variation at different, but overlapping scales. Additionally, both patterns and the processes that drive them are sensitive to the methods that scientists use to study them. Consequently, a variety of experimental and theoretical approaches are necessary to improve our understanding of how organisms, communities, and ecosystems will respond to future change. Collectively, the studies in this thesis employ a diverse array of approaches to test important ecological theories, including long-term observational studies, manipulative experiments, and analyses that leverage both local and global datasets. The Enquist lab has been measuring subalpine meadow carbon fluxes and climate variables at the Rocky Mountain Biological Laboratory (RMBL), for over 13 years at the time of this writing. Examining correlations between climate and carbon flux over this time has led to the identification of interesting patterns between snowmelt, precipitation events, and rates of carbon exchange. Despite the longer growing season, early snowmelt dates ultimately result in lower productivity in these systems. Pairing this study with the results of a soil moisture manipulation experiment aided in the discovery that the strength and duration of the foresummer drought was directly related to rates of carbon exchange and biomass accumulation in these systems. Thus, integrating long-term observational work with an experimental manipulation served to link pattern and process in a way that was not possible with either study alone. The studies in this thesis range in scale from sub-organismal (chapter 3), to community ecosystem (chapters 1 and 2), to continental (chapter 4). Across all scales afunctional trait ecology approach contributes a holistic view of how these changes may impact organismal, ecosystem, and evolutionary responses to environmental variation. Plants are frequently faced with fundamental performance tradeoffs, which arise due to physical, chemical, genetic/evolutionary, and/or ecological constraints. As a result, functional trait measurements can reflect ecological strategies or resource acquisition strategies. Functional ecology offers a promising approach to linking the attributes of individuals to and communities to ecosystem processes. Understanding how individuals, communities, and ecosystems will respond to environmental change is a fundamental question in ecology. I address this topic using a variety of novel experimental methods and statistical techniques. I use a functional ecology approach by considering not only the species in a community, but also the distribution of functional traits that those species represent. It is in this way that I test ecological hypotheses regarding plant responses to environmental change over physiological, ecological, and evolutionary time scales.Release 02-Dec-201