Fall colors in ... Riverside? Stop your snickering

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When people talk about blazing fall foliage in Southern California, they’re usually referring to fire season. Not this year. Cooler temperatures and wimpier winds have turned local leaves into a New England-esque canvas of fiery reds, fluorescent yellows and neon oranges.

It has been an unusually intense, long-lasting display, says John Poimiroo, who tracks autumn scenery up and down the state at Californiafallcolor.com. (Motto: ‘Dude, autumn happens here too.’)

Across Southern California, trees are aglow in rarely seen hues. Crape myrtles, left, typically a lackluster yellow in fall, broke out in pink and scarlet this year. Chinese pistaches added tinges of rose to their traditional orange wardrobe. And Daimyo oaks, a Japanese and Korean native that usually turns ‘a sickly, hideous brown,’ burst into a vivid orange-red, says botanist Frank McDonough, resident answer man for the Los Angeles County Arboretum & Botanic Garden in Arcadia. ‘I’ve been here 12 years and never seen this.’

Several factors influence autumn palettes. Shorter daylight hours trigger the leaf makeover process, shifting deciduous trees to hibernation mode. The chlorophyll that tints foliage green breaks down, bringing yellow and orange pigments to the fore. Red pigments only surface in cold, sunny weather, to protect leaves from sun damage while the tree absorbs their last nutrients, says Louis Santiago, an assistant professor of physiological ecology at UC Riverside. Some trees go two-tone: Leaves facing the sun turn red and the shady side stays yellow.

Normally, most L.A.-area trees don’t reach the red stage, thanks to autumn heat waves and leaf-stripping Santa Ana winds. But this year’s chillier temperatures and weak winds unleashed an exceptional spectrum, from yellow ginkgos and orange bald cypresses to pink tupelos and burgundy flowering pear trees.

Curiously, the plant pyrotechnics started about two weeks later than usual, observers say. Liquidambars, for example, which are specifically bred to produce fall colors in warm climates, tend to peak here around Thanksgiving, McDonough says. This year, they waited until early December.

The belated start and spectacular colors seem to be a statewide phenomenon this season, says Poimiroo, a former state tourism director who launched his autumn blog last year. Poimiroo, who also unveiled a ‘Why go to New England?’ ad campaign in the 1980s to promote fall tourism in Yosemite, insists that California has the cumulatively longest and most varied autumn colors in the nation. The season kicks off in early September in the Sierra, gradually descends through lower elevations and doesn’t fade until December in coastal areas, he says.

Sure enough, earlier this week, Twitter was still crackling with fall foliage reports, from San Diego to Santa Rosa.

But the spectacle is almost over. ‘Enjoy it while you can,’ Santiago says, because many trees have already peaked and the rest should be bare branches by Christmas Eve. -- Roy Rivenburg

Photo, top: The colors peaked on what’s believed to be a Chinese pistache tree in Griffith Park earlier this month. Credit: Anne Cusack / Los Angeles Times

Photo, middle: Crape myrtle leaf detail. Credit: Los Angeles Times

Photo, bottom: The show in Santa Rosa, Calif., on Dec. 8. Credit: Kent Porter / Associated Press