In this article from the Marin Independent Journal, Nick Crawford, sales arborist for Davey's San Francisco office, tells readers what heavy spells of rain can mean for drought-stressed trees.
Posted: March 14, 2016
By PJ Bremier
It’s National Arbor Week. Check your trees.
“Long stretches of drought followed by brief periods of extreme rain stresses trees,” says Nick Crawford of Davey Tree Expert Co. “Heavy rains, high winds, mudslides and recent El Niño storms have damaged, uprooted and killed many local trees.”
Flooding, he adds, “can literally drown a tree’s roots, causing the cells to die from lack of oxygen. The excessive water washes the soil from root zones and that can lead to an unstable trunk.”
Michael Greene, a certified master arborist for Bartlett Tree Experts, is worried about Marin’s trees, too.
“From a structural point of view, more live oaks are falling over than before,” he says. “The ground is so soft for the first time in years now and there’s so much weight on live oaks that it doesn’t take much for them to fall over. “
The most vulnerable oaks grow on slopes.
“They’ve been growing at an angle for years and when there’s excessive rain and lots of water on the canopy, the tree can come over with a big clump of dirt on its root ball with often no decay at all,” he says.
Greene is also concerned about Monterey pines. “The big problem this year is that more of them will be dying as the red turpentine and Ips beetles start flying now through October,” he says. These beetles thrive on stressed trees, introduce their fungus under the bark when they burrow and eventually plug up the tree until it succumbs.
Historically, the red turpentine beetle attacks first, targeting the bottom of a tree, and then the Ips beetle, carrying fungus from dying trees, attacks the top.
“But there are so many Ips beetles and so many dying trees because of the drought now, that we’re seeing Ips beetles attack first,” he says.
Watch for telltale signs of the red turpentine beetle, he says — a gob of what looks like pink Bazooka bubble gum or a pile of rock salt on the bottom of the tree. A dying top signals the infestation of the Ips beetle. It’s too late to save that tree but you can save others by removing the dead tree as soon as possible.
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