Weather hinders oak trees’ growth

SLO County’s oak trees lose foliage and appear dead because of low temperatures in April

David Sneed

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A mid-April cold snap has caused oak trees in the state and in some of the interior parts of San Luis Obispo County to lose their foliage and look dead.

Oak experts with the UC Cooperative Extension report that some oak trees in the Sierra Nevada and coastal mountain ranges are almost completely bare when they would normally be fully leafed out. Other oaks have large numbers of dead leaves.

Doug McCreary, an expert in oak woodland management with the UC Berkeley Cooperative Extension, said the trees are not dead and should bounce back next year.

“Next year, it will probably be very difficult to tell which trees lost their leaves early and which remained foliated late into the season,” he said.

Bill Tietje with the UC Cooperative Extension in San Luis Obispo said the county’s oak woodlands were not hit as hard as those in northern parts of the state because the temperatures here did not get as low. However, temperatures on April 20 dipped below freezing in several inland locations in the county.

Tietje got a call from a North County resident who was concerned about oak defoliation. He also noticed that a valley oak he had planted in San Luis Obispo has brown leaves.

Blue oaks, valley oaks and interior live oaks were the species affected by the freeze, McCreary said. The damage appears to be worse in the mid-elevations of foothills and isolated frost pockets elsewhere.

“The problem for the oaks was that, at the time the freeze occurred, many trees were just starting to leaf out,” he said. “The recently emerged leaves were very succulent and tender and, consequently, vulnerable to the low temperatures.”

San Luis Obispo County is known for its oak woodlands. With 724,000 acres of them, the county is only second to Monterey County in the state which has nearly 1 million acres, according to the UC Extension’s Integrated Hardwood Range Management Program.

The mid-April freeze also damaged vineyards and orchards in the northern part of the state.

Reach David Sneed at 781-7930.