Global warming: Invasive grasses to thrive in warmer world

Global warming will put native grasses at a disadvantage to invasive species.

Consequences include loss of native species, greater wildfire risks

By Summit Voice

SUMMIT COUNTY — The warmer and drier conditions predicted across the West by most climate change models will help invasive grasses replace native vegetation. The exotics are better equipped to deal with warmer weather. Some of them harbor animals that attack endangered species, while others make lands more susceptible to wildfires.

Two researchers at the University of California, Berkeley, catalogued the ranges of all 258 native grasses and 177 exotic grasses in the state and estimated how climate change – in particular, increased temperature and decreased rainfall – would change them. They concluded that many of the traits that now make exotic grasses more successful than many natives also would allow them to adapt better to increased temperature and likely expand their ranges.

“When we looked at current patterns, we found that warmer temperatures favor certain traits, and these are the traits possessed by exotic species,” said coauthor Emily Dangremond, a graduate student in the UC Berkeley Department of Integrative Biology. “This led us to predict that, if the mean temperature increases in all zones in California, there is an increased likelihood of finding exotic species, and an increase in the proportion of species in a zone that are exotic.”

The trait-based approach used in functional biology enables researchers to predict the consequences of global warming and extrapolate the findings to grasslands beyond California.

The increase in exotic species could increase the risk of wildfires, since the non-native grasses dry out more in the summer than native grasses. Some grasses serve as reservoirs for viruses and other pathogens that attack food crops, while others more efficiently suck up water that would normally be used by other grasses and plants.

Dangremond is involved in a study of European beachgrass (Ammophila arenaria), which she has found harbors deer mice that eat endangered lupines. The beachgrass has invaded sand dunes along much of the coast in California, Oregon and Washington, she said.

Exotics have several traits making them more adaptable to higher temperatures. They tend to be taller, have longer and wider leaves, higher specific leaf area, higher nitrogen mass in the leaves and higher seed mass, and were less likely to be perennial. Noxious invasives were even more extremely adapted to warmer temperatures.

These traits account for the success of invasive exotic grasses, Dangremond said. Taller grasses, for example, give exotics more light-capturing ability and the ability to outcompete natives for light. Similarly, the larger seeds of exotic species could give these grasses a competitive advantage at the seedling stage.

“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,” Ackerly wrote. “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.”

“I hate to be a doomsayer, but the problem is getting worse because of humans,” Dangremond said. “Humans promote the spread of invasive species by disturbing areas and letting weedy species come in, and grazing herbivores like cows and elk tend to have a negative effect on native plants anyway. Native species really have a lot to contend with now.”

The study has been accepted for publication in the journal Global Change Biology.

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