The Sandhill Cranes at the Cedar Creek Ecosystem Science Reserve. (Photo: Cedar Creek Ecosystem Science Reserve)

When people intervene in the environment by, say, cutting down trees or spreading fertilizer around, it often results in less biodiversity. Long term, that's a scary prospect—among other things, biodiversity is essential to maintaining a robust food supply. Now, a series of experiments in the Minnesota grasslands suggests that not only is biodiversity essential for ecological stability, but anything that affects stability—fertilizers, say, or clearing land—does so because of its influence on biodiversity.

Ecologists have known for a while that forest fires, water shortages, and the introduction of additional nutrients into the environment might affect biodiversity. Nevertheless, the studies that establish those connections generally don't examine how biodiversity and other key variables, including biomass production and its year-to-year stability, connect with each other, argues a team of researchers led by Oxford University biologist Yann Hautier.

To investigate that relationship, Hautier and his team drew on 12 experiments on grassland ecosystems at the University of Minnesota's Cedar Creek Ecosystem Science Reserve. Those experiments, some of which have been ongoing for 28 years, looked at the effects on biomass production of a wide variety of factors, including the use of fertilizers, fire suppression, and directly controlling the number of plant species on a plot of land. When they analyzed the data, the researchers found no clear connection between biodiversity and biomass productivity, or the variability of productivity year to year.

It didn't matter what experimenters manipulated—if it lowered biodiversity, it lowered the stability of the ecosystem as well.

But when the team focused on stability—defined as the ratio of biomass productivity to its year-to-year variation—they found that biodiversity consistently increased stability. That was true whether experimenters directly controlled the number of species present but also when they'd influenced species diversity through other variables, such as the amount of nitrogen in the soil. In other words, it didn't matter what experimenters manipulated—if it lowered biodiversity, it lowered the stability of the ecosystem as well.

Those results strongly suggest that however we manipulate the natural environment, it's those manipulations' impact on biodiversity that ultimately determines how stable an ecosystem is, the researchers argue in a paper out tomorrow in Science.

"Our work suggests that conservation policies should encourage management procedures that restore or maintain natural levels of biodiversity or minimize the negative impacts of anthropogenic global environmental changes on biodiversity loss to ensure the stable provision of ecosystem services," the team writes.

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