Scientists focus on endangered prairies

more than 90 percent of biodiverse prairies in the Northwest have vanished
more than 90 percent of biodiverse prairies in the Northwest have vanished

For the imperiled prairies of the Pacific Northwest, the equation is simple, says Environmental Studies professor Scott Bridgham: Germinate or die.

Bridgham, associate professor Bart Johnson of Landscape Architecture and a large team of postdoctoral associates and graduate students recently investigated the effects of climate change on native plant range distributions and community structure of Pacific Northwest prairies, a once dominant ecosystem now rapidly vanishing. The project was funded by the Department of Energy’s Office of Biological and Environmental Research.

Many consider loss of biodiversity the only truly irreversible global environmental change that Earth faces. The problem is acute in the Pacific Northwest, where 90 percent to 99.9 percent of the species-rich historical prairies have disappeared.

Among other questions, Bridgham’s team sought to understand how climate change will affect the distribution, abundance and fitness of native and exotic grasses and wildflowers in the prairies, and in what ways the species’ sensitivity to climate change differs as they approach or go beyond their current northern range limits.

Bridgham’s team studied three prairies across a 520-kilometer range from Washington to southern Oregon, with sites located in Rainier, Wash., Eugene and Selma. Seeds of native species were planted and followed through two annual cycles as the team manipulated climates by adjusting heat and precipitation.

The study showed that higher temperatures harmed species planted within their current range, but did not affect those that had been moved north of their current range. The best predictor of the plants’ survival was whether they were able to germinate despite the change in climate.

“Across all sites and treatments, germination was the most critical stage,” Bridgham said. “If you germinated, you tended to survive.”

The study suggests that one way to preserve the diversity of the prairies in the face of climate change would be to move species north of where they currently exist. But that approach is considered highly controversial by conservation groups because of potential negative effects on local genetic diversity, Bridgham said.

In a companion study, Bridgham’s team studied the potential for climate change to cause an increase in carbon dioxide release due to an increase in the respiration of roots and soil microbes. There is widespread concern that because grasslands contain vast amounts of soil organic carbon, future climatic warming will increase soil respiration and, thus, exacerbate human release of greenhouse gases.

They found that warming of soils in southern Oregon had little effect on soil respiration because of severe drought during the growing season as compared to large temperature effects farther north. If future climate change increases summer drought conditions farther north, as is predicted, soil respiration in the northern range may become less sensitive to warming over time, or even suppressed, Bridgham said.

“While the negative effects of climate change on biodiversity are of great concern,” Bridgham said, “our study suggests that the soil carbon feedback to climate change in grasslands may be less severe than other studies have indicated.”

- by communications specialist Matt Cooper, UO Office of Strategic Communications