CLIMATE EXTREMES IN GRASSLANDS: WHAT’S NEXT?

Abstract

As a consequence of warming temperatures under climate change, precipitation extremes like drought, wet years, and deluges (large rainfall events) are increasing. Increasing hydrological extremes have been observed across many ecosystem types, but grassland ecosystems may be particularly vulnerable as they are typically water-limited and highly sensitive to changes in precipitation amount and patterns. Prior research demonstrates the strong relationships between precipitation and grassland structure and functioning, but numerous studies have also identified high variability in grassland responses to that same amount in precipitation in different years. Legacy effects, or the effects of climate extremes that persist after an extreme subsides, are one explanation for variability in responses. Alterations in resources or ecosystem structure may begin during a climate extreme and persist after the extreme ends as legacies. Legacy effects in grasslands may be positive, negative, or a combination of both. Most of our understanding of legacy effects comes from observational and experimental studies that evaluate responses following the end of some extreme period. However, increases in “hydroclimate whiplash” – or rapid transitions between dry and wet extremes – and consecutive drought or wet years are expected under future climate change. Thus, it is increasingly important to study the interactive effects of past and current extremes. In this dissertation, I use data collected from both field experiments with precipitation manipulations and during natural extreme years to compare grassland responses to extremes and legacy effects following extremes. Each chapter of my dissertation presents results at least in part from the semiarid shortgrass steppe in northern Colorado, USA – spanning over a decade of data altogether – to compare legacy effects at multiple temporal scales and from several types of precipitation extremes. My research overall demonstrates the high sensitivity of grasslands to changes in environmental conditions, especially in the shortgrass steppe, and provides examples of both positive (greater responses than expected) and negative (lower than expected) legacy effects following extremes. The results of my dissertation contribute to our understanding of legacy effects and interactions of past and future extremes. These results can be used to make better-informed management decisions in grasslands threatened by climate extremes, and should be built on in the future with further study of the mechanisms of legacy effects of extremes.