New Study Challenges Ideas on Plant Diversity

September 23, 2011 - News Release

It’s time to scrap the textbook model used for decades to explain plant diversity in grasslands in Canada and worldwide, according to a paper published this week in Science by a global team of ecologists that includes a University of Guelph researcher.

The authors call for new models to help understand and manage these increasingly threatened ecosystems, including Western Canada’s oak savannah, the salt marshes of the American South, the alpine meadows of Europe and Africa’s Serengeti plains.

The paper describes a worldwide study that tested the so-called “hump” model of grassland diversity used for more than 30 years. Referring to the paper’s results, Prof. Andrew MacDougall, Department of Integrative Biology, said, “I think it’s the death of the hump.”

That longtime model says grasslands in differing climates or continents should develop in the same way. “In ecosystems with limited productivity, for example, there is low diversity because only a few different plant species are able to handle the poor growing conditions,” he said.

Past the hump’s peak, the amount of material — plant productivity for ecologists — keeps rising. But diversity, or species richness, then falls as only a few top plants come to dominate the ecosystem.

Ecologists and resource managers have applied this productivity-species richness relationship to predict how periodic burns and the culling of grazing animals might affect the restoration of native grasslands.

This new global study by 58 researchers on five continents disproves that classic relationship, said MacDougall. Measuring plant productivity and species richness in nearly 50 plant communities in North America, Africa, Europe, Asia and Australia, the scientists found no consistent pattern linking productivity and species diversity.

In their paper, the team members call for ecologists to develop new approaches to studying these complex ecosystems, including factors such as grazing impacts and human disturbance.

MacDougall said the accepted productivity-richness relationship had made intuitive sense; undergrads still find it in many ecology textbooks. More and more, ecologists had begun to question it.

Running this global experiment allowed the collaborators to test the model properly. Until this year, MacDougall had been the only Canadian researcher on the team since it began in 2007. He works in Garry oak savannah on Vancouver Island.

A University of Toronto researcher has since joined the group. A new researcher in Argentina has also widened the team’s scope to South America. Including other new members, the network — co-ordinated by researchers at the University of Minnesota — now runs in more than 70 sites worldwide.

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