Warmer temperatures to expand California exotic grass populations

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Warmer temperatures in California could lead to a substantial statewide expansion of exotic grass populations, according to a new study that catalogued over 400 native and exotic grasses in the state.

Researchers from UC Berkeley say exotic grasses dry out faster than native varieties, making the state more vulnerable to wildfires. Exotic grasses also hold pathogens that attack crops, such as wheat, or affect people who eat beef from cows that graze on exotic species. They also compete with native grasses for water.

“As climate changes in the coming century, which at this point is quite certain, this means we expect the distributions of the grasses to change as well,” said David Ackerly, a UC Berkeley professor of integrative biology and the inspiration behind the study. “Sadly, what this predicts is that the alien species that already dominate the Central Valley and other hotter regions of the state will become even more widespread in the future.”

Since 2008 Ackerly has studied functional ecology, which measures the role plants play in the ecosystem and how those roles may alter with climate change. Functional ecology is being used to predict the consequences of global warming in California, which models predict will be between 2.2 and 5.8 degrees warmer by 2100.

“Over the next century, changes in the global climate are expected to have major consequences for plant communities, possibly including the exacerbation of species invasions,” the study said.

Using functional ecology, Emily Dangremond, a graduate student in the UC Berkeley department of integrative biology, and postdoctoral fellow Brody Sandel, now at Aarhus University in Denmark, divided the state into 800 zones. In each, they catalogued the grasses and mean temperature.

Dangremond and Sandel found zones with warmer temperatures tended to have more exotic species that had traits more adaptable to warmer temperatures. Exotic grasses on average were taller, had longer and wider leaves, and had larger seed size than native grasses, allowing for more light-capturing ability. Their larger seeds also give them a competitive advantage over native grasses.

“Given the current pattern, we’re predicting in a climate change scenario, the climate will act as a filter, favoring plants that have traits adaptable to higher temperatures,” Dangremond said.

Dangremond said the study shows there are going to be more invasive plant species in the future, but the consequences aren’t yet clear. “This study is meant to say we need to be more vigilant of invasive plant species since we predict their populations will increase,” Dangremond said.

The yearlong study is available online and published in the journal Global Change Biology.

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