Trees out on a limb

Arborist says mature evergreens at special risk for drought stress

“Brown is the new green” signs are sprouting in yards all over the Bay Area as more residents are letting their landscapes go dry in response to the drought. But one place you may want to continue letting water flow is to your mature trees.

“The crunch that everyone’s trying to resolve is that they’re cutting back on water use because we have to, but they don’t want to lose trees, especially mature trees that have been growing for decades,” says Nicholas Crawford, board certified master arborist with the Davey Tree Expert Co. in San Francisco.

“The risks of not watering trees outweigh those for other landscape plants and turf. Lawns can go dormant and will rebound, but with trees, you don’t have that option.”

When the weather is warm and it hasn’t rained for a couple of months, trees may suffer from drought stress. That shows up as leaves that are wilting, browning at the edges, dropping at an unusually high rate, or a canopy is more sparse than normal.

Along with increasing property values, trees help clean the air of pollutants, control erosion, reduce runoff after storms and create

shade that lessens the need to use energy for cooling. The more mature the tree, the greater the benefit.

If a lawn, perennials or shrubs die from lack of water, they’re relatively inexpensive to replace. But losing a mature tree can be pricey.

Removing a dead tree can cost hundreds or even thousands of dollars, depending on the size and situation; if you choose to have a new one planted, you’ll incur the costs of installation as well as of the tree itself. And over time, you’ll end up using more water.

“When you replace a tree, you end up with a much smaller tree, you re-set the environmental benefits, and it takes much more water to grow that tree to its mature size than if you’d provided supplemental water to your mature tree during the drought,” Crawford says.

Evergreen trees are most at risk. While it’s normal for deciduous trees to create and lose a new set of leaves every year, evergreens rely on leaves that are more than a year old to generate enough energy to survive. And if drought causes premature leaf loss, the tree declines.

“When the leaves are dropping and turning brown, the stress is so great that it’s hard to recover,” Crawford says.

Brant Ward / The Chronicle Nicholas Crawford, master arborist with Davey Tree Expert Co., checks a drip watering system in S.F. that he recommends for mature trees.

Brant Ward / The Chronicle Crawford, exposing the drip system on an S.F. median, says risks of not watering trees outweigh those for other plants and turf.

Brant Ward / The Chronicle Homeowner William Wood takes a pan of water from a bucket that gathers water in his kitchen sink, to water trees in his S.F. backyard.