Water & Drought

UC Davis study finds dry weather threatening California wildflowers

Wildflowers flourish along a trail below the summit of Mt. Tallac in Lake Tahoe in summer 2013. Mt Tallac is one of the iconic hikes in Tahoe. UC Davis researchers, in a report published Monday, found that dry, hot weather has caused wildflower diversity to decline.
Wildflowers flourish along a trail below the summit of Mt. Tallac in Lake Tahoe in summer 2013. Mt Tallac is one of the iconic hikes in Tahoe. UC Davis researchers, in a report published Monday, found that dry, hot weather has caused wildflower diversity to decline. rpench@sacbee.com

Dry, hot weather has reduced the diversity of California’s beloved native wildflowers, perhaps irrevocably, according to a new study from University of California, Davis researchers.

California is home to thousands of native wildflower species, which have been threatened for decades as non-native species, development and agriculture have encroached on their habitat. The drought and climate change pose new challenges.

The period between December and February has for the last 15 years been marked by long periods of dry, sometimes hot, weather. Such weather causes the upper layer of soil to dry and makes it hard for wildflowers to grow, UC Davis researchers found.

“Fifteen years ago, you had just these wonderful wildflower years,” said Susan Harrison, a UC Davis professor of environmental science and policy and the lead author of the study, which was published Monday in the journal Proceedings of the National Academy of Sciences. “The good years aren’t quite as good anymore and the good years aren’t as frequent anymore.”

Dry weather in midwinter affects annual California wildflowers when they are tiny seedlings, Harrison said.

If those seedlings are merely lying dormant, the trend observed by Harrison may not have dire effects, she said. The seeds, under this scenario, will simply sprout once it starts to rain.

But if the seedlings are sprouting and then dying quickly due to lack of water, it may not be easy for California’s wildlife population to fully recover.

Harrison is focusing future research on which scenario is likely to play out.

At stake is the “diversity” of California’s native plants, she said. “Diversity is a term for the number of species.” Without diversity, she said, California plant populations would become “a monoculture.”

Dan Gluesenkamp, executive director of the California Native Plant Society, said the UC Davis research is important but inconclusive. California has a broad range of ecosystems, and wildflowers behave differently in each of them.

“In California, variability is the norm,” he said. “They have 15 years of data. … For a California grassland, that’s not a lot of time.”

Gluesenkamp, whose organization has roughly 10,000 paying members, said the best way to protect California native plants is to identify which plants are threatened and set aside habitat for them in trusts and parks. He also called for more native plant restoration.

“I wouldn’t worry about the sky falling because of climate change,” he said. “But keep watching.”

Harrison said she would love for her research to be proven wrong. However, the data gathered over 15 years at the McLaughlin Reserve, part of UC Davis’ Natural Reserve System, showed negative trends across a broad spectrum of plants.

“California native-dominated grasslands are getting very, very rare,” she said. “The climatic trends are probably widespread. There is no reason to think (the McLaughlin Reserve) is different or exceptional.”

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