Prairies from California to Washington state are catching the heat not just from wildfires but also from warming temperatures. For ranchers, it all means stress on pastureland.

Two newly launched University of Oregon projects, funded by separate federal agencies, will help better understand the effects of rising temperatures and changing precipitation patterns on both native plants and forage crops, most of which were brought into the area as ranchers moved west.

In Oregon and Washington, Lucas Silva is subjecting diverse prairies and pastures to conditions expected in the next 50 years to see how they respond and share carbon and nutrients through below-ground networks. Northeast of Sacramento, Lauren Hallett is testing whether compost amendments being added to increase grassland forage and carbon sequestration — an approach being used by ranchers — has different effects depending on rainfall conditions.

Silva and Hallett are assistant professors in the UO’s Environmental Studies Program.

“These are historically managed systems,” said Silva, who began preparing three research plots last month for two years of experiments beginning next spring under a grant from the National Science Foundation. “In thinking about the ranchers, a question is whether monocrop pastures and diverse prairies behave differently under drought stresses.”

Silva, also a faculty member in the Department of Geography, will be looking at how native and forage grasses use soil resources, especially carbon and nitrogen, and whether there are networks of exchange between them and soil fungi.

“We have pasture and prairie replicated at our sites across three different latitudes,” he said. “By experimentally manipulating temperature and rainfall across these sites, we can determine if there is a climate threshold at which pasture or prairie resilience will be lost.”

Silva’s plots were previously used by UO scientists Scott Bridgham, Bart Johnson, Bitty Roy and Laurel Pfeifer-Meister under a five-year National Science Foundation grant and an expired Department of Energy grant. Their work has resulted in a series of papers, which overall reflect what Bridgham calls the Californication of Pacific Northwest prairies.

Warming, Bridgham said, could negatively affect native species at the northern edge of their ranges unless they can move further north, either naturally or by assisted migration.

“Warming will likely drive prairie plant communities from their current state of primarily perennial species to exotic annual grasses, similar to prairie communities in California,” he said.

That, he said, likely will have affects on wildlife and livestock, fire dangers and pollination, he added.

Soil moisture and temperature are important in controlling soil respiration in the prairies. The moisture is key in the dry springs and summers of Southern Oregon whereas temperature is important further north in somewhat wetter growing seasons, Bridgham said.

Silva will leverage that previous work, focusing on the moisture factor in the networking of soil carbon and nutrients in root-fungi connections. His team will inject gases into each site to feed the plants and their root fungal partners under stressful conditions.

“We’re testing how plants talk to each other, and trying to figure out the rules that govern this communication,” Silva said.

Hallett, with a grant from the U.S. Department of Agriculture, is working at the Sierra Foothills Research and Extension Center, which is operated by the University of California system. Her team will add soil amendments and manipulate rainfall amounts.

The research is driven by recent practices by ranchers who have been applying compost on their pastureland in a project with Whendee Silver of University of California, Berkeley. That effort, Hallett said, has resulted in a pronounced increase in carbon uptake by the soil and may provide ongoing benefits.

A remaining question is whether the effects are resilient under variable rainfall conditions, said Hallett, who also is a faculty member in the Department of Biology.

“We are looking at potential synergies and tradeoffs on the ecosystem as a result of this strategy of adding compost,” she said. “We’ll have a compost amendment, which is mostly organic nitrogen from processed waste, and another treatment will be inorganic nitrogen fertilizer. These will be compared with unmanipulated areas.”

Over three years, her team will hit the areas with extreme wet or drought conditions using shelters and irrigation. It is hoped that the project will speak to the sustainability of using compost as a climate-mitigation strategy and help ranchers understand additional benefits or potential costs.

“One of the major things we can do for mitigation is to add and store more carbon than we emit,” she said. “The goal is to test whether a strategy to store carbon in soil will affect other things we value, such as forage for our cows to eat and native plant diversity.”

—By Jim Barlow, University Communications