The Global Expansion of C4 Ecosystems

FIGURE 5 Histograms comparing the carbon isotope ratio values for fossil tooth enamel older than 8 Ma (lower charts) with those that are younger than 6 Ma for six regions of earth adopted from Ceding etal. (1998a). 

Stable-isotope studies of paleosols from Pakistan and East Africa are in good agreement with the paleodietary studies. The Siwalik sequence in Pakistan has excellent exposures covering the last 20 Ma. 5 C studies of paleosol carbonates show a virtually pure C3 ecosystem up to about 7.5 Ma ago, a transitional period of ecosystem change lasting 1-1.5 Ma, and then C4-dominated 

The quantum-yield model predicts that important changes in the global proportions of C4 biomass occurred during the Pleistocene 

CO2 record Byrd ice core Antarctica Neftel etal (1988) 

FIGURE 7 Predicted relative carbon gain by the quantum-yield model and therefore predicted competitive success by C,- and C4-grass canopies across the Great Plains of North America under today s atmospheric carbon dioxide levels. Noted are the predicted cross-over points from Cy to C4-dominance based on the quantum-yield model and the observations for soil organic matter (Tieszen et al 1997) and for aboveground harvests (Epstein etal, 1997). Adopted from Ehleringer (1978). 

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