Urban trees dying in drought. What you need to know

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Limiting outdoor water use might be inadvertently creating a new casualty of the drought: trees.

Experts say many trees in Southern California are showing signs of drought stress or are outright dying due to lack of water.

As people stop watering lawns, many are also not watering trees, leading them to dry out and become vulnerable to disease and pests.

Losing mature trees not only hurts the urban ecosystem, it also can cause local temperatures to rise and home values to drop.

Here's what you need to know about urban trees and the drought.

Trees do a lot of good

It might go without saying, but trees in urban areas, or "street trees" as they are known, are really great to have around.

Not only do they look good, they also provide homes for animals, cool neighborhoods, clean the air and even raise property values.

In fact, a recent study from the US department of Agriculture found street trees in California provide one billion dollars in benefits every year.

Los Angeles has about 700,000 trees; neighboring Santa Monica has roughly 33,000.

It's not clear how many are stressed, but Hector Kistemann, Public Landscape Manager for Santa Monica, says it's likely every tree in his city is affected in some way.

Each tree lost to drought would cost thousands of dollars to remove, replant and regrow, not to mention the decades it would take for them to fully mature. 

Know the signs of a drought-stressed tree

It's not always easy to spot a parched tree, but there are some obvious signs to look for says Cy Carlberg, a consulting arborist currently working with Culver City. 

"Leaves can curl up and drop off, branches die," she said.

Some trees may turn yellow or even red out of season as the chlorophyll inside their leaves die off, she explained.

In deciduous leaves, look for wilting, scorched looking sections and browning between veins.

For evergreens, needles may change to a red or yellow color, and they may brown at the tips.

Symptoms may take a long time to appear, so it's best to err on the side of keeping trees healthy and happy while they are still green.

Dry trees are easy targets for pests

Water doesn't just keep a tree green, it also helps them fight off invaders.

Trees like the Canary Island Pine secrete resin to keep bugs from eating into their bark. Without sufficient water, they are unable to pump out as much resin.

"Most trees in fact become very susceptible to boring insects if they become water stressed," said Timothy Paine, a professor of entomology at UC Riverside.

Paine says all sorts of tree pests are thriving because of the dry weather.

As they grow in numbers, these bugs begin to attack more and more trees, sometimes even harming drought-tolerant ones.

Even drought-tolerant trees need to be weaned off water

Sure, it's a good idea to scale back on outdoor watering during a drought, but don't cut your trees off cold turkey!

"It needs time to get use to not having that water," said Rachel Malarich of the environmental group TreePeople.

Even native or drought-tolerant plants need time to adjust to a new watering cycle, she explained.

So if a tree previously was being watered every day by lawn sprinklers, that process should be slowly wound down over weeks and months.

In fact, Malarich says some trees can take up to five years to adjust to drier conditions.

To properly water a tree, don't treat it like grass!

The good news about trees is that they don't need daily waterings.

"Trees would prefer to a have large amounts of water less often," said Linda Eremita, an arborist with TreePeople.

For mature trees that have acclimated to drier conditions, she says you should only need to give it a soak once a month, depending on the soil and type of tree.

Younger trees may need weekly waterings.

Either way, the goal is to get water to the roots, which can be a foot or more below the surface.

Eremita recommends using an inline emitter to do that, which is basically a hose that slowly dribbles out water in multiple spots.

Spiral that out from the trunk and it’ll soak the roots.

Rachel Malarich, also with TreePeople says after that, add mulch.

"It helps keep that moisture in the soil," she explained.

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