RUI/Collaborative Research: The Rise of C4 Grasses in South America: Linking Grassland Transitions to the South American Summer Monsoon

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Grasses cover a large portion of the Earth and provide many staple foods for humanity. However, there is considerable disagreement on how grasslands will respond to environmental change, and the potentially dramatic changes to crop productivity, species invasions, and biodiversity remain unknown. Without a firm understanding of the climatic conditions that caused the spreading of warm-season grasses in the deep past, it is difficult to predict how they will respond in the future. The significant enlargement of grasses' geographic range millions of years ago during the Miocene is the focus of this study. This project is the first to collect data on precipitation and vegetation during the Miocene in South America and to use it to make simulations of ancient climate during this important ecological change. Results are leading to new understanding about how the abundance of warm-season grasses may change in natural and managed landscapes in response to future environmental changes.The Late Miocene expansion of C4 grasses is one of the most dramatic ecological changes in the past 65 million years. In order to predict how these economically important grasses will respond to future enviornmental change, the factors controlling their past distributions must be understood. In South America, C4 grass expansion was coincident with a strengthening of the South American Summer Monsoon and regional tectonic changes. This project is combining multi-proxy paleovegetation reconstructions with proxy-based paleoclimatic reconstructions and paleoclimatic modeling techniques to understand the linkages between tectonics, climate, and environmental change in South America. Results are leading to new understanding of the conditions under which C4 grasses expanded. A societal benefit of this research includes the ability to make better predictions for how the abundance of C4 grasses may vary in natural and managed landscapes in response to future environmental changes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.