Researchers find biodiversity key to global ecology

Joanna Dornfeld

University researchers think they’ve proven why biodiversity is so important to global ecosystems.

Ecology professor David Tilman published his group’s controversial findings in last week’s edition of Science that shows more plant species growing in an ecosystem increase productivity and efficiency.

Diverse ecosystems can help the global environment by removing carbon dioxide from the atmosphere or purifying water. But biodiversity – a variety of organisms co-existing in the same ecosystem – is decreasing throughout the planet.

“We should understand what effects simplifying systems has on (the ecosystems),” Tilman said.

Before Tilman published the initial findings in 1994 and 1996, most ecologists believed diversity destabilized ecosystems. But Tilman hypothesized the number of plants in an ecosystem not only stabilizes the community but also increases species productivity – or yield – and increases the amount of minerals the soil maintains.

His hypothesis challenged previous theories and sparked debate within the ecology field in 1997 when other scientists published papers contradicting his hypothesis.

“Controversy means it’s a time when lots of ideas were being generated,” Tilman said. “And frankly, I think it was a wonderful time for our discipline.”

Previously, Tilman had conducted an experiment suggesting the number of plant species in an ecosystem increased productivity and efficiency, but diversity was not controlled. So Tilman conducted an experiment to test the hypothesis with controlled diversity.

“It makes certain amounts of biological sense,” said Susan Galatowitsch, ecology of horticultural science associate professor. “I think it’s still a bit controversial at this point that biodiversity confers resilience.”

Tilman and his colleagues planted 168 plots of natural prairie grasses in 1994. Different plots were seeded with plant species ranging from one to 35 species. The group planted 18 different species, randomly planted in the plots.

The group found that the more plant species in a plot, the greater the total yield. They also found more diverse plots retained minerals in the soil more efficiently.

When there are multiple species in an ecosystem, there are increased opportunities to correct problems naturally, Tilman said.

The effects of diversity will be important for managing ecosystems in the future. The diverse plots removed carbon dioxide from the atmosphere 2.7 times faster than plots with only one species.

If the same kind of processes happen in forests as in grasslands, climate change could be slowed, Tilman said. Forests remove carbon dioxide from the atmosphere more efficiently than grasslands.

The majority of managed forests are planted with only one species. However, diverse forests could remove larger amounts of carbon dioxide from the atmosphere.

Diverse ecosystems could also improve natural water purification, therefore reducing the need for expensive water treatment plants, Tilman said.

“It suggests we should look at other services species provide,” he said.