Drought watering regulations may leave trees high and dry
08/04/2014 12:00 AM
10/06/2014 8:26 PM
Ray Gulliksen sees the dead branches topping his birch trees as a signature of the drought.
The trees in his Fair Oaks front lawn are “showing quite a bit of stress,” he said.
The stress comes from watering restrictions that are turning lawns brown around the region and could also weaken trees, arborists warn.
Gulliksen has turned off his sprinkler system and cut his watering by half. He now waters once a week for 20 minutes. “I don’t feel like we’re giving the trees enough water, but I don’t want to use any more water than I have to,” he said.
New state water regulations approved last month by the State Water Resources Control Board call for steep cutbacks in lawn watering and other water uses. In Sacramento, the city has for months limited outdoor irrigation, including parks.
At present, Sacramento waters its parks in 10 to 20 minute increments, twice a week, as part of its water conservation plan. That watering is applied at three different start times within that 20 minutes.
“It’s not designed to be constant watering,” said Elizabeth Anderson, operations manager with the city’s department of Parks and Recreation,
That kind of watering suffices for lawns but not for trees, said John Lichter, arborist for the Davis-based Tree Associates.
A watering of 20 minutes is inadequate to bring enough water to the deep roots of some trees, said Lichter.
Lichter, who is also a consulting arborist for the city of Elk Grove, advocates for deep watering –which means soaking trees for more than an hour, sometimes two. He said deep watering should be done at least once every three weeks, and sometimes every two weeks depending on the drought tolerance of the tree. Younger trees will need more water than older, mature trees.
Lichter has encountered homeowners that are unaware of the effect reduced watering is having on their trees.
“I’m hearing a lot of folks telling me they’re not watering their lawns anymore,” Lichter said. “They ask me for a pruning estimate, and I tell them: ‘Do you want me to give you a pruning estimate if a lot of your trees are going to die?’ ”
In Davis there is no shortage of stressed or dying trees, said Bob Cain, urban forest manager for the city.
The city of Davis is responsible for taking care of 22,000 trees. The rest – 60 percent – exist on private land.
Tree failures in the city have been increasing. In 2012, there were 152 tree failures in Davis. In 2013 there were 203, according to Davis city data.
“A lot of the water-saving measures in town are exacerbating this,” Cain said. “People are just not watering their lawns. And the soil moisture is very low.”
Chronic water stress over long periods weakens trees and eventually kills them. Drought stress also makes trees more vulnerable to attacks by pests and disease.
Not much research has been done on urban trees and drought stress. More is understood about forests and drought stress. A study by the UC Cooperative Extension, which examined the effect of the prolonged drought of 1987-92, established that it hastened the demise of many oak trees in the state.
Which trees will be most affected depends on the soil and how they are irrigated. In Davis, Cain is seeing most stress among the Modesto ash species as well as among pear trees.
“In some cases the trees are dying,” said Cain.
Trees in the city of Sacramento are still faring reasonably well, said Joe Benassini, urban forester for Sacramento. “That’s not to say that we will not see anything later on in the season,” he said.
Drought stress may not be apparent in some trees, and may take years to show, he said.
Benassini said he thinks the older tree stock in the city and better soils in midtown and in south Sacramento may account for the healthier condition of the trees in the city.
Some of the stressed-looking trees in the city probably started to decline some time ago, before the current watering restrictions kicked in, he said. “That stress you’re seeing in trees? That is a result of years of inadequate irrigation over a prolonged period,” he said.
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