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Why did California's high winds fell so many trees?

December 2, 2011 |  1:28 pm

Why did the powerful Santa Ana winds that hit Southern California this week fell so many trees?

Experts said one reason was that the winds were remarkably choppy and unpredictable.

In some places, winds suddenly shifted from 10 mph or 20 mph to more than 80 mph. The shift made trees as well as roofs and power lines vulnerable.

PHOTOS: Santa Ana winds | Submit your photos

"Everything lined up perfectly," said Bill Patzert, a climatologist for Jet Propulsion Laboratoryin La Cañada-Flintridge.

Trees were no match for the winds, especially those with heavy canopies. Patzert noted that trees in urban Southern California neighborhoods don't have the strong root systems found in more natural environments.

"L.A. trees don't have deep roots. The urban forest is artificial and is primarily watered by lawn sprinklers," Patzert said. "So what keeps our urban forest alive is people watering their lawns, which are not natural, so you don't have deep root systems. So our trees are very vulnerable to Santa Ana events."

Walter Warriner, a Santa Monica arborist and community forester, agreed, adding that the large canopies of many local trees lack strong foundations.

"When you look at a tree above ground there's a ratio of 20 to 1 compared to below ground, so there's not that many roots holding our big trees in place," he said.


Second round of high winds still expected, forecasters say

Santa Ana winds: Rare weather system produced powerful gusts

Santa Ana winds: Pasadena neighborhood boxed in by fallen trees

--Hector Becerra and Matt Stevens