The greater the biodiversity, the better the chances of grassland restoration, researchers find

Monday, February 18, 2013

by DIANNE FETTERLY

University of Guelph researchers are recommending growers consider adding several species of vegetation if considering restoring marginal fields to grasslands.

Dr. Andrew MacDougall, a professor and grasslands specialist at the university said a 10-year study conducted on Vancouver Island shows that encouraging several species of vegetation on marginal fields and woodlots will provide a beneficial crop cover, whereas having just one or two species of plants may not survive in the case of a major disturbance such as fire, flood or drought.

“If you don’t have extreme drought, then you can do well with just one or two species of cover,” he said.“But if drought continues to become more prevalent, then farmers could benefit from planting a diversified species of native grasses.”

MacDougall and his team conducted their study in the island's savanna/ grasslands. He explained that when European settlers came to the area in the mid-1800s they operated mixed farms geared primarily towards dairy cattle. Over the years, much of the native grasses were replaced with pasture grasses like Orchard Grass and Kentucky Blue, and after 150 years of these types of management practices, coupled with intensive grazing, the grassland was converted from high diversity to a low diversity of just a few species.

Researchers wanted to determine what, if any, were the effects of the loss of biodiversity.

In order to demonstrate outside disturbances to the grasslands, MacDougall’s team first burned off the grassland area, followed by subsequent fires in later years.

“Within the first year we saw changes,” he said.

As long as the system remained unaffected by outside disturbances such as fire or drought, “there was no detectable effect of diversity loss,” he explained. “But when perturbation did finally occur, the effects of diversity loss were revealed . . . system collapse except where collections of native species still happened to remain.”

The area grown to the European pasture grasses was incapable of handling the sudden and intense disturbance, resulting in an invasion of trees. But the land covered in the remaining native species did very well after the burn and actually resisted the establishment of trees, MacDougall said.

After a major disturbance, the system with just one or two plant species breaks down, and other species, such as trees, take over . . . then we just end up with the plants that are able to adapt, explained Kevin McCann, a Guelph professor who specializes in ecosystems. It was “surprising how quickly the system recovered following such a sudden and intense disturbance,” he added.

McCann said he sees advantages to farmers in returning marginal fields to grasslands beyond environmental benefits. Having a more diverse variety of plant species around the edges of fields could foster natural predators, which, in turn, would help control pests in the crops, he said.

The researchers' work was recently written up in Nature magazine. BF