The Dry Garden: Plant guru Peter Raven on how climate change will prompt change at home


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As the program had it, the ceremony at Rancho Santa Ana Botanic Garden in Claremont was to honor Peter Raven. But those who came away from Sunday’s event might be forgiven for believing that Raven, the man Time magazine called a “hero for the planet,” had come to honor Rancho Santa Ana.

For those unfamiliar with Raven, he is to plants what David Attenborough is to animals. He co-authored the seminal textbook “The Biology of Plants” and advised the Clinton administration on biodiversity. Under his directorship for almost four decades, the Missouri Botanical Garden (the oldest botanic garden in continuous operation in the country) became a lifesaver for the sweeping Flora of North America project. Soon Raven will be in London, at the Chelsea Flower Show, an American lecturing the English on the future of sustainable gardening.


It merits adding here that Raven is not just American, but Californian, born in San Francisco in 1936. As a 1999 profile in Time noted, “at 8 he became a student member of the California Academy of Sciences. At 12 he joined the Sierra Club. At 15 he discovered a member of the heather family, a Presidio manzanita, which had not been seen for 50 years. This subspecies, Ravenii, was later named for him.”

After attending UC Berkeley and then UCLA, early in his career Raven spent a year as taxonomist and herbarium curator at Rancho, one of Southern California’s premier botanic gardens dedicated to native flora. Marking National Public Gardens Day, Raven returned to Claremont to discuss Rancho Santa Ana’s future and the role of botanic gardens in general.

Referring to Rancho’s founder, Susanna Bixby Bryant, and the formation of the original garden in the era of silent films and flappers, Raven told the gathered Southern Californians, “Mrs. Bryant never really thought about conservation. She certainly thought that California was changing and what should we do about it and let’s keep some of the plants, but no one in 1927 could have foreseen the terrible threats to species that we have today.”
It would be inaccurate to describe Raven’s address Sunday as doom-laden, but he did not dance around the uncertainties posed by climate change. “The Intergovernmental Panel on Climate Change estimates that from 20% to 40% of all species in the world will be extinct by the end of this century,” he said. “That’s a horrendous figure.”

The good news for Southern California, he told the audience, is that our region is already the product of a cataclysm. We have lessons all around us in adaptation in the face of what at the time was a disaster, and so do a handful of regions like ours.

Those regions, like Los Angeles, are dotted between the 30th and 40th parallels of the northern and southern hemispheres. Their floras were sharply altered after glacial events back in the day, meaning the Miocene, sent cold ocean currents ripping past hot land. This transformed what probably had been subtropical climates into ones marked by long dry seasons and the almost complete absence of summer rainfall. Now known as “Mediterranean climate zones,” these regions cover most of California and the Mediterranean basin along with parts of Chile, South Africa and Australia.

“When the rains stopped in the summer, a lot of plants dropped off,” he said. But then something so dazzling happened that Raven confessed to the group that the way he visualizes it is as “a crystal in a kaleidoscope.” As water-hungry flora died off, speciation filled in the breach. Our hallmark chaparral community shrubs such as manzanita and Western lilac emerged. “Consider that buckeyes have their leaves in the summer across most of the country,” Raven said, “but the California buckeye has no leaves in the summer, but leaves in the winter.”


The geography of California is so varied, the emerging plant genera threw off unknown numbers of distinct species adapted to often terribly specific conditions in mountains, coastal plains, deserts and stream banks. As such, California’s myriad microclimates are identified by botanists like Raven by following “[northern] maples down to the Santa Monica Mountains and desert plants all the way up to the Bay Area.”

According to Raven, what we face now in climate change is another big climactic event. Given human-acceleration of climate change coupled with population growth and finite natural resources, the evolutionary power of plants may not be able to keep pace. Our native flora most certainly holds the answers of what will survive, but the what, how and where parts are unclear.

To cope, Raven argues, we must know the existing flora and be able to call upon species with the best ability to adapt. And so he told the audience Sunday: Botanical gardens must become seed banks, collecting and preserving what grows now and what might prove right for the future.

While they’re at it, he added, public gardens must also re-educate us.

“Botanical gardens emerged as medicinal gardens, to grow herbs to see what would cure people. Then, in 18th century, they became showcases of the diversity of the plants found by explorers. In the modern era, botanical gardens must be a major force to educate people.” Raven would like to see water conservation, cultivation and care of native flora, food production, runoff prevention and topsoil preservation as priorities.

Can our public gardens adapt fast enough? For that matter, can we? Raven has faith. Look at how we tackled smog, he said. “When I first moved to L.A. in 1956, it was still mandatory to burn all your combustible trash in an incinerator in your back yard. By 1957, it was strictly prohibited.”
“It makes sense that we’ll come to a point where we’re sustainable,” he said. “The question we must ask ourselves now is how long it will take and what we will lose in the process? What kind of a landing do we want to have? What kind of world do we want to live in? We need to put forth an enormous energy to keep the kind of world we really want.”

-- Emily Green

Green’s column on sustainable gardening appears here weekly.

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