Flower di­ver­sity di­min­ish­ing

Sci­en­tists see cli­mate change in ac­tion in Cal­i­for­nia wild­flower fields as some species are re­duced.

Los Angeles Times - - CALIFORNIA - SASHA HARRIS- LOVETT sasha. harris- lovett @ latimes. com Twit­ter: @ sasha_ hl

Drier, sun­nier win­ters are stress­ing Cal­i­for­nia’s wild­flow­ers.

These twin trends have con­spired to re­duce the di­ver­sity of wild­flower species in a North­ern Cal­i­for­nia re­search meadow by 15% over 15 years, ac­cord­ing to a study pub­lished this week in the Pro­ceed­ings of the Na­tional Academy of Sciences.

The re­sults of­fer clear ev­i­dence that cli­mate change af­fects plant di­ver­sity on a lo­cal scale, said UC Davis ecol­o­gist Elise Gor­nish, who worked on the study.

“Cli­mate- driven di­ver­sity de­cline is oc­cur­ring at a scale that is vis­i­ble to the rel­a­tively ca­sual ob­server,” Gor­nish and her col­leagues wrote in the study.

The wild­flower loss was ev­i­dent even when the re­searchers ex­cluded data from 2013 and 2014, when Cal­i­for­nia’s drought kicked into high gear.

The UC Davis team didn’t set out to study the ef­fects of drought or cli­mate change.

When the re­searchers be­gan­they were their cu­ri­ousstudy in about 1999, the ways that cat­tle graz­ing and wild­fires af­fect plant di­ver­sity. Twice a year, sci­en­tists headed north­west to the McLaugh­lin Nat­u­ral Re­serve, a pro­tected area in Napa and Lake coun­ties that is man­aged by UC Davis for re­search pur­poses. Its roughly 7,000 acres serve as a gi­ant out­door lab­o­ra­tory for ecol­o­gists, ge­ol­o­gists and bi­ol­o­gists, along with 38 other wild ar­eas the Univer­sity of Cal­i­for­nia main­tains across the state. “They’re re­ally price­less,” UC Davis plant ecol­o­gist Su­san Har­ri­son, lead au­thor of the study, said of the lands. Over time, the re­searchers no­ticed that the big, in­tense blooms of wild­flow- ers that used to ap­pear in the spring were be­com­ing less and less fre­quent. So they de­cided to an­a­lyze changes in plant species over time.

They picked 80 dif­fer­ent sites from all over the re­serve and counted all of the species grow­ing in five small plots at each site. They also es­ti­mated how much area each plant species cov­ered within each plot.

The re­search team cor­re­lated changes in plant growth with changes in rain­fall pat­terns, tem­per­a­ture, cloud cover and hu­mid­ity.

Across all 80 sites, clus­ters of na­tive wild­flower species be­came in­creas­ingly less di­verse from 1999 to 2014, the re­searchers found. In par­tic­u­lar, the species that were dis­ap­pear­ing fastest were those with broad leaves, which are most sus­cep­ti­ble to drought.

The 15% de­cline in wildf lower species di­ver­sity was cor­re­lated with about 50% less rain in midwinter, about 20% more sun in fall and win­ter, and a 20% drop in win­ter hu­mid­ity.

The down­ward trend in midwinter rain­fall over the en­tire re­serve was par­tic­u­larly strik­ing, the re­searchers said. To­tal rain­fall from De­cem­ber to Fe­bru­ary plunged from about 20 inches in 1999- 2000 to about 10 inches in 2013- 2014.

“There has al­ways been like a week dur­ing Jan­uary where you go around in your shirt­sleeves, but those pe­ri­ods have been get­ting longer and longer — and warmer and drier — in the past 15 years,” Har­ri­son said.

That’s bad news for wild­flow­ers.

Many types of Cal­i­for­nia wild­flow­ers ger­mi­nate in the cool midwinter months, Har­ri­son said. For a seedling to sur­vive long enough to make sturdy roots and send up a f lower, it needs the soil near the sur­face to stay moist. If the soil dries, the nascent wild­flower will wither and die be­fore it can re­pro­duce.

Even if the to­tal an­nual rain­fall were to stay the same, wild­flow­ers can be af­fected by the tim­ing of the storms, Har­ri­son said.

To take ac­count of other fac­tors that might af­fect plant di­ver­sity, the re­searchers made sure about half of the sites were in ar­eas with fer­tile soils, no graz­ing and no re­cent history of fire. The other sites had in­hos­pitable soils, oc­ca­sional graz­ing and had burned in 1999. Even when these vari­ables were con­sid­ered in their model, the link be­tween cli­mate change and wild­flower growth held up.

The UC Davis team is con­tin­u­ing to mon­i­tor the re­search sites to see how de­creases in wild­flower di­ver­sity af­fect larger ecosys­tem pro­cesses such as soil nu­tri­ent cy­cling, pol­li­na­tion and the spread of in­va­sive plants.

But the 80 plots al­ready in­di­cate that Cal­i­for­nia’s grass­lands may look quite dif­fer­ent in win­ters to come, Har­ri­son said.

“In­stead of see­ing a beau­ti­ful dis­play of wildf low­ers, we’d see all grass and no f low­ers, or just a few f low­ers,” she said.

Don­ald & Sylvia McL augh­lin Univer­sity of Cal­i­for­nia Nat­u­ral Reser ve

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