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

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 change(1-3). Here we show, using free-air CO2 enrichment (FACE) technology in an intact Moja ve Desert ecosystem(4), that new shoot production of a dominant perennial s hrub is doubled by a 50% increase in atmospheric CO2 concentration in a hig h rainfall year. However, elevated CO2 does not enhance production in a dro ught year. We also found that aboveground production and seed rain of an in vasive annual grass increases more at elevated CO2 than in several species of native annuals. Consequently, elevated CO2 might enhance the longterm su ccess and dominance of exotic annual grasses in the region. This shift in s pecies composition in favour of exotic annual grasses, driven by global cha nge, has the potential to accelerate the fire cycle, reduce biodiversity an d alter ecosystem function in the deserts of western North America.