UNCORRECTED PROOF Carbon isotope evidence for an abrupt reduction in grasses coincident with European settlement of Lake Eyre, South Australia Beverly J. Johnson, 1 * Gifford H. Miller, 2 John W. Magee, 3 Michael K. Gagan, 4 Marilyn L. Fogel 5 and Paul Quay 6 ( 1 Quaternary Research Center and the School of Oceanography, University of Washington, Seattle WA 98195-7940, USA; 2 Institute of Arctic and Alpine Research and the Department of Geological Sciences, University of Colorado, Boulder CO 80309-0450, USA; 3 Department of Geology, The Faculties, Australian National University, Canberra 0200, ACT, Australia; 4 Research School of Earth Sciences, Australian National University, Canberra 0200, ACT, Australia; 5 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC 20015, USA; 6 School of Oceanography, University Washington, Seattle WA 98195-7940, USA) Received 17 February 2004; revised manuscript accepted 23 December 2004 Abstract: Stable carbon isotopes in emu eggshell (EES) reflect emu diets and consequently the vegetation availablefor food sources. At Lake Eyre, South Australia,isotopic data suggest that there has been a rapid and dramatic change in vegetation at some point over the last 200 years when compared with the rest of the Holocene. The proportion of C 4 plants in emu diets has been reduced by approximately 20% in response to an overall shift in C 4 /C 3 biomass at Lake Eyre. Isotopic measurement of the dominant plants at Lake Eyre indicate that the C 4 plants are almost entirely comprised of grasses and some chenopods and the C 3 plants are comprised of the dominant chenopods, shrubs, trees and forbs. We surmise that the /20% reduction in C 4 plant biomass reflects landscape degradation and loss of C 4 grasses resulting from a combination of effects, including overgrazing by both introduced (e.g., sheep, cattle and rabbits) and native (e.g., kangaroos) animals, increasing drought and a change in fire regime beginning in the late 1890’s. The magnitude of vegetation change that occurred in the last 200 years is as great as that which occurred during the last glacial maximum ( /21000 years ago), and provides the first evidence for major environmental change at Lake Eyre soon after Europeans settled the arid zone. Key words: Australia, European settlement, environmental change, carbon isotopes, emu, eggshell, plants, grasses, historical change. Introduction Vegetation changes related to the most recent migration of humans into Australia (i.e., European settlement beginning over 200 years ago in AD 1788 (summarized in Flannery, 1994)) have been documented in the semi-arid regions of eastern Australia for the last century (summarized by Noble, 1997). For example, a decrease in perennial grass biomass resulting from the introduction of grazing animals (e.g., sheep and cattle) is thought to have led to a decreased fire frequency and a subsequent rise in woody shrubs in semi-arid western New South Wales (Harrington et al., 1979; Duyker, 1983; Hodg- kinson and Harrington, 1985; Noble and Grice, 2002). Isotopic evidence corroborating the aforementioned trends is relatively *Author for correspondence. Present Address: Department of Geology, Bates College, Lewiston, ME 04240, USA. (e-mail: bjohn503@ bates.edu) Y:/Arnold/HL/Articles/HL861ra/HL861ra.3d[x] Monday, 23rd May 2005 14:33:14 The Holocene 15,6 (2005) pp. 890  /898 # 2005 Edward Arnold (Publishers) Ltd 10.1191/0959683605hl861ra