Warmer Winters Threaten California Wildflowers

In California, the species diversity of native wildflowers is shrinking, following several years of drier winters, says a new study.

Drought-intolerant species suffered the worst declines, the researchers confirmed.

The study is based on 15 years of monitoring about 80 sampling plots at McLaughlin Reserve, part of University of California, Davis’ Natural Reserve System, and shows the first evidence of climate change impacts on the state’s grasslands.

Lead author Susan Harrison, environmental science and policy professor, said:

“Our study shows that 15 years of warmer and drier winters are creating a direct loss of native wildflowers in some of California’s grasslands. Such diversity losses may foreshadow larger-scale extinctions, especially in regions that are becoming increasingly dry.”

Comparable trends have been observed in other Mediterranean environments, for example southern Europe, strengthening the case for increased climate change awareness in the world’s semi-arid regions.

Combined with climate change predictions, this means the future grassland communities of California are expected to provide less nutrition to herbivores, be less productive, and become more vulnerable to invasion by exotic species, the study says.

The researchers expect these negative effects to trickle up through the food web, affecting insects, seed-eating rodents, birds, deer, and domesticated species like cattle, all of which rely on grasslands for food.

It may be possible for wildflowers and grasses to cope with the current drying period through their deep seed banks, which can lie dormant for decades waiting for the right conditions to germinate. But California’s drought is expected to exacerbate in the coming decades, so rescue effects may end up being too late for some species.

Susan P. Harrison, Elise S. Gornish, and Stella Copeland
Climate-driven diversity loss in a grassland community
PNAS June 22, 2015 doi: 10.1073/pnas.1502074112

Photo: Peter Kemmer/flickr