Even After Heavy Rain, Trees May Need Help Surviving Drought

The drought is officially over, but its effects might continue for our area's trees.

The Washington region has experienced severe droughts in four of the past six years. Last summer's was the worst since the one in 2002, which rivaled the Dust Bowl of the 1930s. But no drought could survive the 9.21 inches of rainfall the Washington region received from May 1 to 21, more than three times the average moisture for this time.

You can track rainfall on the U.S. Drought Monitor Web site ( http://drought.unl.edu/dm/monitor.html). The site, operated by the Agriculture Department, the National Oceanic and Atmospheric Administration, and the University of Nebraska's National Drought Mitigation Center, also includes climate predictions, stream flow, drought severity, soil moisture forecast maps and a host of other information.

"I heard on the radio that the water table is back to normal because of record-setting rain this spring," said Rebecca Feldberg, arborist for Baltimore. "But that doesn't mean that the effects of the drought will not still be felt." She believes that last summer's dryness is still hurting our trees.

Many appear healthy, but questions remain: Will they survive this growing season or show serious stress by midsummer? Will any loss of trees be because of the severity of last year's drought, the cumulative effect of a six-year deficit or just part of the cyclical nature of climate?

Feldberg said she's seen large trees, 50 to 60 feet tall, that seemed perfectly healthy last year fail to leaf out this spring. But she said the most profound effect has been on young trees planted last year; despite a continuous watering program, many haven't survived.

Baltimore encourages homeowners to help by watering street trees. Residents who request to have trees planted in front of their houses are asked to commit to watering them for two years. At this time, it's not necessary to irrigate because there has been plenty of rain, Feldberg sad. However, during the dry summer months, she recommends giving trees 10 gallons of water twice a week.

Water can be applied in a variety of ways. One of my favorites is a do-it-yourself technique using one-gallon plastic jugs filled with water, with four or five small holes punched in the bottom. Set 10 of those around each tree, or more if necessary, depending on its size. Most of the water will drip directly into the area where the tree can absorb it.

Newly planted and young trees are not the only ones that require water during dry spells. Mature trees also benefit from irrigation when the weather is dry. However, even with diligent watering, trees can display stress from heat and lack of aeration to roots because tap water doesn't oxygenate roots in the same way as rainwater.

The value of the ample rainfall we have received this spring is about to be tested. Some arborists and other horticultural experts suggest that the droughts in recent years have caused root damage that will show itself this summer when trees use last year's food stores prematurely and perhaps defoliate before making enough food for next year.

We have a backyard forest of mature white oaks, hickories and tulip poplars, and we'll be monitoring any early defoliation to test the accuracy of these theories.

I have seen many browning white pines this spring, and I thought it was because of insects, disease or drought. The only time I have ever witnessed so much needle drop on white pines was from weevil damage, but I have seen no signs of that pest.