Fire, Atmospheric pCO2, and Climate as Alternative Primary Controls of C4-Grass Abundance: The Late-Quaternary Perspective

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Grass-dominated ecosystems cover about one-third of Earth's land surface, influence global biogeochemical processes (e.g. water, carbon, and nutrient cycling), and serve as major food sources for humans and herbivores. These ecosystems are among the most sensitive to future changes in climate and atmospheric chemistry. This sensitivity can be partially attributed to the differential responses of two major functional groups, C3 and C4 plants. C4 plants gain competitive advantages under certain environmental conditions (e.g. fire, heat, drought, and low pCO2). C3 and C4 plants in turn have distinct influences on major biogeochemical processes; for example, the role of C4 plants in global net primary production is disproportionately large. Despite these well-known differences, it remains controversial what environmental factors directly control the relative abundances of C3 and C4 plants. Paleoecological studies can help decipher the responses of C3 and C4 plants to a wide range of environmental conditions, thereby offering information for anticipating future changes. This project will evaluate the effects of fire, climate, and atmospheric CO2 concentration on the variation of C4-grass abundance over the past 25,000 years in East Africa and Australia. The researchers will analyze sediment cores for a suite of ecological proxy indicators and develop a novel technique to estimate the abundance of C4 plants in geological records. This project provides an excellent context for educating the general public on climate change and grassland ecology. The researchers will organize summer courses targeting middle and high school teachers as well as land managers.