Simulated global environmental changes impact plant diversity

In a high-performance machine, each part is essential to the overall function of the whole. In ecology, species diversity is necessary to the smooth operation of the ecosystem. Until recently, little attention has been paid to the potential ecological effects on plant diversity from combined global environmental changes including increased atmospheric CO2, warming, elevated nitrogen pollution, and increased precipitation. Scientists from the Carnegie Institution’s Department of Global Ecology in Palo Alto, California, and Stanford University published a study on this subject in the June 16-20, 2003, Proceedings of the National Academy of Sciences Online Early Edition. “We were surprised at how quickly some environmental changes can alter the complexion of an ecosystem,” said Erika Zavaleta, the study’s lead author and a new member of the faculty at the University of California, Santa Cruz. The finding is significant for understanding what can happen to ecosystems when confronted with the interrelated climactic and atmospheric changes that are observed today and that presage larger changes in the future.

The Carnegie and Stanford scientists conducted their three-year study in the Jasper Ridge Biological Preserve – a typical California grassland where the 43 plant species are a mixture of grasses and wildflowers. “We simulated a series of possible future environments for California, with four global change factors: elevated CO2, warming, nitrogen pollution, and added precipitation, alone and in combinations. Different combinations with altered levels of two, three, and four of these variables are likely to reflect future conditions in different parts of the globe,” said Chris Field, director of the Carnegie Institution’s Department of Global Ecology and coordinator of the Jasper Ridge study.

“At the end of three years, we found that treatments with three of the four experimental treatments changed total plant diversity. Elevated CO2 reduced diversity as did adding nitrogen. More water increased plant diversity and, warming alone had no effect,” Zavaleta explained. The four treatment combinations that represent likely possible futures all resulted in decreased wildflower diversity; but total diversity was not affected because there was an increase in the grasses. The largest loss of wildflower diversity came with elevated CO2 plus warming and nitrogen pollution, and all four of the factors combined. “Given the importance of the wildflower species for wildlife, nutrient cycling, and natural beauty, the losses under realistic global changes are a cause for concern,” said Zavaleta.

Field emphasized: “Over the last century we have witnessed an 30% increase in atmospheric CO2 , an overall global warming of about 1 F, increases in nitrogen pollution from human activities, and changes in rainfall patterns. We are in the process of determining how the interactions among these components are affecting the health of the planet. This study and others like it at Global Ecology can provide some sorely needed answers.”

The Jasper Ridge Global Change Experiment was supported by the National Science Foundation, the David and Lucile Packard Foundation, the Morgan Family Foundation, the Jasper Ridge Biological Preserve, and the Carnegie Institution. The Carnegie Institution (www.CarnegieInstitution.org) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments in the U.S.: Embryology, Geophysical Laboratory, Terrestrial Magnetism, The Observatories, Plant Biology, and Global Ecology.