Previous studies have shown that for specific ecosystem services, such as nutrient cycling, biodiversity did not seem to matter. "You could lose species without seeing much impact," says ecologist Andrew Hector of the University of Zurich, who partnered with fellow ecologist Robert Bagchi of the University of Oxford on the new research. "We found that higher levels of biodiversity were required to support ecosystem functioning in total."
Basically, different types of grassland plants provide varying types of services, with some overlap. "When we looked at the groups of species that affected different pairs of ecosystem services, they shared only one fifth to one half in common," Hector notes. By tracking as many as seven ecosystem services—ranging from clean water to total production of hay—they found that a panoply of plant species was required to maintain these functions.
The research, published in Nature, primarily examined plants and to a lesser extent microbes and insects. "The same idea could apply [to insects and germs]," Hector says. "Loss of biodiversity could lead to vacant or underexploited niches and this could have a negative impact on ecosystem functioning and services."
Hector, for one, has moved on to the Sabah Biodiversity Experiment, designed to examine this question in the tropics. Experimental plots of roughly 3,000 square acres have been planted with either one, four or 16 different species of dipterocarp trees—the tallest trees in the rain forest of Malaysian Borneo, which have been largely eliminated by logging. "We want to know if replanting with a more diverse mixture of species can help restore fully functional forest ecosystems when compared to the more usual practice of planting [one]," he says. Indications from the grasslands of Europe are that he will need as many species as he can get.