Wednesday, Aug. 29, 2007

NIH trees under stress from drought

Caretaker says canopy is healthy overall

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Motorists on Rockville Pike have noticed a worrisome sight: stressed trees at the National Institutes of Health in Bethesda.

This is something the NIH canopy shares with trees in Montgomery County, as the flora of Bethesda recuperates from a bout of rough weather.

Throughout the campus of more than 300 acres on Rockville Pike, trees are recovering slowly but surely.

‘‘They can appear to be sickly,” Lynn Mueller, chief of NIH ground maintenance and landscaping, wrote in an e-mail to The Gazette. ‘‘Their leaf tips will dry out and curl to conserve internal moisture. Deep green spring leaf color will fade,” but ‘‘overall they are not suffering from any disease.”

The campus has lost about 40 of its 8,000 trees this year. Drought stress is mostly to blame for the deaths, but February’s month-long freeze and recent scorching temperatures put more strain on the trees. No trees have been removed because of disease or infestation, according to Mueller.

Some trees along Wilson Drive are showing the effects of a project completed in 2004 to build a deep underground utility tunnel on the campus.

The trees that lived alongside the tunnel excavation were fed and aerated before construction began, Mueller explained, but ‘‘a dozen of the poplars down hill of the tunnel, or down stream of the water table, have died.”

After examining them and finding they had died, Mueller removed the trees’ side limbs and upper crowns — ‘‘topping” them — and left the trunks standing. Their decaying bark will attract insects, woodpeckers, nuthatches, titmice, chickadees, blue birds and squirrels, he said.

Concerns have been raised by Bethesda and Chevy Chase residents about home construction endangering trees in residential neighborhoods. But on the NIH campus, above-ground construction is not a major threat to trees, according to Mueller.

The main threat in recent months has been drought and extreme temperatures. This is typical in the area, according to Michael F. Galvin, Maryland Department of Natural Resources urban forestry supervisor.

‘‘It’s kind of like, you can’t not drink a glass of water for two months, and then drink a gallon at once,” Galvin said. Most of the forestry from Baltimore south is stressed by severe drought, he said.

Unlike most forested zones in Bethesda, the NIH campus is overseen by a federal team instead of state or county arborists. The 158 species of NIH trees are entered into an electronic tracking system that allows Mueller to quickly identify trees and monitor their health. He uses a device called a Resistorgraph to test sick trees for rotting interior if he finds fungus, open cavities or limb damage during a routine inspection.

The NIH plan mandates a one-for-one replacement of trees that must be removed.

‘‘Two for one is better,” said Caren Madsen of the Montgomery County Sierra Club chapter. Madsen noted that replanted trees can have trunks as small as one inch in caliper. ‘‘That’s basically deer food,” she said.

‘‘They’ll take a tree out that’s 27 inches in diameter, and replace it with a sapling, and say that’s one on one,” said Ralph Schofer, who represents the Maplewood Citizens Association on the NIH’s Community Liaison Council. ‘‘On the other hand, there’s no way they can transfer a 27-inch tree.”

Schofer echoed other sentiments from the council that residents are mostly pleased with the NIH tree maintenance program.

The Montgomery County forest conservation law requires that trees be reforested at a ratio of one-quarter acre to 2 acres planted for every one acre removed.

According to state foresters, the NIH canopy that buffers the campus from surrounding neighborhoods and makes northern Bethesda ‘‘green” is well above average.

‘‘I would consider them kind of the gold standard,” Galvin said.