Elevated CO2 increases productivity and invasive species success in an arid ecosystem

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Arid ecosystems, which occupy about 20% of the earth's terrestrial surface area, have been predicted to be one of the most responsive ecosystem types to elevated atmospheric CO2 and associated global climate change1,2,3. Here we show, using free-air CO2 enrichment (FACE) technology in an intact Mojave Desert ecosystem4, that new shoot production of a dominant perennial shrub is doubled by a 50% increase in atmospheric CO2 concentration in a high rainfall year. However, elevated CO2 does not enhance production in a drought year. We also found that above-ground production and seed rain of an invasive annual grass increases more at elevated CO2 than in several species of native annuals. Consequently, elevated CO2 might enhance the long-term success and dominance of exotic annual grasses in the region. This shift in species composition in favour of exotic annual grasses, driven by global change, has the potential to accelerate the fire cycle, reduce biodiversity and alter ecosystem function in the deserts of western North America.

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Figure 1
Figure 2: The relative ratio (elevated CO2/ambient CO2) of plant density (left), above-ground plant biomass (centre) and seed rain (total seed production; right) per unit area at the Nevada Desert FACE Facility in May, 1998.


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We thank D. Jordan, E. Knight, G. Hendrey and the Brookhaven National Laboratory for technical support; C. Biggart, L. DeFalco, C. Grant, E. Hamerlynck, M. Hargrove, K. Hightower, K. Huxman, F. Landau, D. Pataki, K. Salsman, T. Shiver, D. Stortz-Lintz, and M. Taub for field and laboratory assistance; and J. Titus for soil nitrogen data. Financial support was provided by the DOE- and NSF-EPSCoR programs and panel grants from NSF/TECO and DOE/TCP, and additional support was provided by the NAES. We also thank the DOE/Nevada Operations Office and Bechtel Nevada for site operations support.

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Correspondence to Stanley D. Smith.

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