The Heat Is Online

Enhanced CO2 Will Cut Plant Diversity

Global warming may wipe out a fifth of wild flower species, study warns

The Independent (U.K.), 17 June 2003

One in every five species of wild flower could die out over the next century if levels of carbon dioxide in the atmosphere double in line with predictions, scientists said yesterday.

A study of the impact of global warming on plants has found that most of the environmental changes are likely to result in a substantial loss of plant life. Even though plants need carbon dioxide to survive, the research found that higher levels of the gas reduced numbers of wild flowers by 20 per cent, and cut overall plant diversity by 8 per cent.

Scientists from Stanford University in California altered the environment of 36 open-air plots of land - on which between five and 20 wild plants had been growing - over a period of three years. They doubled carbon dioxide, increased "rainfall" by 50 per cent, caused average temperatures to rise by 1.7C and added nitrogen pollutants to the soil - all of which are likely to happen because of global warming. The researchers, who published their study in the Proceedings of the National Academy of Sciences, described the findings as "dramatic".

Plots that received all four treatments - which emulated the environmental conditions likely to exist 100 years from now - suffered a decline of 25 per cent in wild flowers and even those given extra nitrogen or carbon dioxide suffered a 10 or 20 per cent decline.

Only increased watering resulted in a rise in diversity. The scientists suggested that increased carbon dioxide, temperature and nitrogen allowed some plants to grow faster for longer, making it difficult for other plants to survive.

Professor Christopher Field, who led the study, said the team was surprised to find that increased carbon dioxide and watering caused such opposite effects given that they were both essential for plants to grow.

"One hypothesis is that elevated carbon dioxide added moisture to the soil, which tended to extend the growing season of the dominant plants, leaving less room for other species to grow," Professor Field said.

His colleague, Erika Zavaleta, said the study demonstrated how some wild plants would suffer while others benefited from the effects of climate change. "Certain kinds of species are much more sensitive to climate and atmospheric changes than others. It turned out that wild flowers were much more sensitive to the treatments than grasses were, no matter what combination of treatments we tried," Dr Zavaleta said.