As winter storms rage on, water-saturated ground and high winds are putting trees at risk -- and trees across the Bay Area are no exception.
Since Dec. 31, when a series of strong storms began moving through the area, Palo Alto's Public Works Department has responded to at least 100 tree calls related to the wet and windy weather, according to city arborist Pete Gollinger.
"Public Works staff have been responding to storm emergency calls virtually around the clock since New Year's Eve," he said.
The city also has brought in two tree contractors to assist with the tree work, he added.
"Every situation is unique," he said. "Most whole tree failures observed during the recent storms were due to high winds occurring during a period of super-saturated soils."
At least eight calls involved trees causing impacts to power lines that led to significant power outages, according to the city. In one case, an 80-foot-tall, 20-inch diameter tree came down and blocked Page Mill Road near Hanover Street.
Downed trees have accounted for only a portion of calls for service during the storms, Gollinger said. Other types of calls have included flooded roadways, clogged storm drains and debris removal.
Thomas Whitney, a technical adviser with The Davey Tree Expert Company, said in a statement that soil saturation and wind are the main culprits bringing down trees.
"Roots attach to soil, so if soil is displaced, the tree is prone to uprooting," he said. "Pervasive drought and/or recent fire also can weaken tree roots and predispose the soil to these issues."
Strong winds also can overpower the strength of a tree's root system, Whitney said.
With storms coming one on top of another, Gollinger said, the water has no time to move down to the water table, leading to "supersaturated soils."
"If high winds occur while the soil is still saturated, we see a larger number of whole tree failures than if the storms were spaced further apart," he said.
Homeowners can do little to prepare their trees for the current storms, but, Whitney said, it's important to care for trees year-round to build their resilience for more extreme weather. Homeowners can promote healthy soil and fine root development by mulching around trees, watering during dry periods and conducting soil renovation if necessary.
If a tree owner is concerned or wants to be proactive, Gollinger recommended hiring a certified arborist to evaluate trees in question.
Whitney agreed. For now, while the winter storms continue, Whitney recommended leaving tree care to experts, with the exception of already-fallen wood.
"Arborists are trained to deal with storm damage safely. Dead trees or broken limbs are extremely dangerous when they are still suspended above the ground," he said.
To report fallen trees in Palo Alto, call Palo Alto Public Works at 650-496-6974 on weekdays from 7 a.m. to 4 p.m. and 650-329-2579 after hours. For emergencies, call 911.