The Stresses of Summer Force Trees' Survival Out on a Limb

While forest fires in the West have captured the nation'sattention, a similar but less visible disaster has been wreakinghavoc with East Coast trees: an arboreal broil caused by thissummer's record-breaking drought and high temperatures.

From Georgia to New Jersey, extreme water shortages and heat waveshave placed even drought-resistant trees under severe stress, causingearly leaf loss, increased susceptibility to disease and prematuredeath.

In metropolitan areas such as the District and its Virginia andMaryland suburbs, trees are taking an even bigger hit because cityroads, sidewalks and buildings radiate extra heat and because sparseurban rainfall typically gets diverted into storm sewers before treeshave a chance to sate their thirst.

"I don't mean to sound alarmist, but this is the worst crisis fortrees along the eastern coast of the United States since the chestnutblight at the beginning of the century," said Kim D. Coder, aprofessor at the University of Georgia's Warnell School of ForestResources in Athens. That fungal disease all but wiped out theAmerican chestnut, which until 1900 was a dominating presence in EastCoast hardwood forests.

It's not just this year's scorching weather that's bringingEastern trees to their knotty knees, Coder said. Much of the regionhas been parched for three or four summers in a row. So instead ofputting on inches and pounds during the summer growth season, treeshave been raiding their own precious carbohydrate food stores. ManyEast Coast trees have just about used up those reserves and are nowputting their last bursts of energy into especially large batches ofacorns or cones -- a classic response to extreme environmental stressthat says, in effect, "I may not make it, but the next generationmight."

"Especially in urban centers," Coder said, "we are at the end ofwhat these trees can handle."

That's bad news for people, as well as for trees, urban foresterssay. In populated areas, trees do much more than give residents shadyrespite. They cleanse the air of pollutants such as nitrogen dioxide,sulfur dioxide, carbon monoxide and ozone. And evaporation from treeleaves pulls significant amounts of heat from the urban atmosphere,lowering air temperatures and reducing the need for air conditionersat night.

Perhaps because trees seem so stoic and impervious to stress --and perhaps because urban citizens overestimate the level of carelocal governments can offer their trees -- residents too often failto help these woody giants in their time of need, experts say.

Water is the key. Although last week's rain provided some short-term relief, the showers had no significant impact on the overalldrought, weather service officials said. Trees can lose hundreds ofgallons of water on a single hot day, so they need a fairly regular,if modest, supply. About 90 percent of water-absorbing tree roothairs are in the top foot of soil, so as little as an inch of waterdripped or sprinkled around a tree once a week can save it frombecoming next year's chain saw fodder.

And although scorched leaves are already hitting the ground inmany neighborhoods, it's not too late to help, said Bonnie Appleton,a Virginia Tech extension specialist with the Hampton Roadsagricultural research center in Virginia Beach. Many trees are justnow making their leaf and flower buds for spring. "If people watertheir trees now," Appleton said, "it can have a big effect nextyear."

A couple of inches of mulch can also do a lot to maintain soilmoisture between waterings. But this is not the time to addfertilizer, Appleton said, which can be harmful to leaves and rootsduring periods of water stress.

Trees face a central problem during hot and dry periods: They needcarbon dioxide from the atmosphere to perform energy-capturingphotosynthesis, yet there is no way to let that gas into the plantwithout at the same time losing precious water to the atmosphere.

Gas intake and water loss occur through tiny leaf pores calledstomata. During midday temperature highs, stomata close to minimizewater loss -- putting a crimp in photosynthesis that the plant cantolerate for limited periods. During long days and weeks of extremelyhigh temperatures, however, stomata stay shut to save water, andtrees find themselves in an energy crunch. Photosynthesis slows oreven stops and, gradually, leaves are dropped.

If leaf loss is scattered throughout a tree, it can usually besaved with added water, experts said. But if a tree is losing majorhanks of foliage, especially around the crown, then energy storeshave probably been emptied, and the tree is dying.

Even when water is available, extremely high temperatures can harmtrees directly. The enzymes that facilitate the chemical reactionsthat keep trees alive operate best between 70 degrees and 80 degreesFahrenheit. When temperatures hit the mid-90s, photosynthesis startsto shut down. In the 100-degree range, fatty elements of tree cellmembranes start to "melt," and chlorophyll molecules break down.

At about 115 degrees, enzymatic molecules literally fall apartinside cells, and tree tissues suffer irreparable damage that canspread with each new day of unrelenting heat.

City trees get even hotter than their country counterparts,because solar energy bounces off concrete and brick surfaces asinfrared radiation, adding 9 degrees to 12 degrees to the air wellinto the night. Passing cars and trucks, whose surfaces in summer canexceed 120 degrees, add to the heat load on leaves. And roots, whichwork best at temperatures between 60 degrees and 80 degrees andgenerally stop functioning when soil temperatures exceed 95 degrees,can find themselves roasting, because summer soil temperatures canexceed 100 degrees.

Street cuts to accommodate utility work and road resurfacing takefurther tolls on urban trees by disturbing delicate root hairs. MarkBuscaino, the District's chief forester said that although 4,000streetside trees are being planted annually in Washington, losseshave long been outpacing gains.

A study of Washington tree cover over the 25 years ending in 1997,conducted by American Forests, found that tree canopy had declined byabout 44 percent.

"Every tree out there is a miracle," Buscaino said.

A miracle that this year could use a helping hand.

The Stresses of Summer Force Trees' Survival Out on a Limb

While forest fires in the West have captured the nation'sattention, a similar but less visible disaster has been wreakinghavoc with East Coast trees: an arboreal broil caused by thissummer's record-breaking drought and high temperatures.

From Georgia to New Jersey, extreme water shortages and heat waveshave placed even drought-resistant trees under severe stress, causingearly leaf loss, increased susceptibility to disease and prematuredeath.

In metropolitan areas such as the District and its Virginia andMaryland suburbs, trees are taking an even bigger hit because cityroads, sidewalks and buildings radiate extra heat and because sparseurban rainfall typically gets diverted into storm sewers before treeshave a chance to sate their thirst.

"I don't mean to sound alarmist, but this is the worst crisis fortrees along the eastern coast of the United States since the chestnutblight at the beginning of the century," said Kim D. Coder, aprofessor at the University of Georgia's Warnell School of ForestResources in Athens. That fungal disease all but wiped out theAmerican chestnut, which until 1900 was a dominating presence in EastCoast hardwood forests.

It's not just this year's scorching weather that's bringingEastern trees to their knotty knees, Coder said. Much of the regionhas been parched for three or four summers in a row. So instead ofputting on inches and pounds during the summer growth season, treeshave been raiding their own precious carbohydrate food stores. ManyEast Coast trees have just about used up those reserves and are nowputting their last bursts of energy into especially large batches ofacorns or cones -- a classic response to extreme environmental stressthat says, in effect, "I may not make it, but the next generationmight."

"Especially in urban centers," Coder said, "we are at the end ofwhat these trees can handle."

That's bad news for people, as well as for trees, urban foresterssay. In populated areas, trees do much more than give residents shadyrespite. They cleanse the air of pollutants such as nitrogen dioxide,sulfur dioxide, carbon monoxide and ozone. And evaporation from treeleaves pulls significant amounts of heat from the urban atmosphere,lowering air temperatures and reducing the need for air conditionersat night.

Perhaps because trees seem so stoic and impervious to stress --and perhaps because urban citizens overestimate the level of carelocal governments can offer their trees -- residents too often failto help these woody giants in their time of need, experts say.

Water is the key. Although last week's rain provided some short-term relief, the showers had no significant impact on the overalldrought, weather service officials said. Trees can lose hundreds ofgallons of water on a single hot day, so they need a fairly regular,if modest, supply. About 90 percent of water-absorbing tree roothairs are in the top foot of soil, so as little as an inch of waterdripped or sprinkled around a tree once a week can save it frombecoming next year's chain saw fodder.

And although scorched leaves are already hitting the ground inmany neighborhoods, it's not too late to help, said Bonnie Appleton,a Virginia Tech extension specialist with the Hampton Roadsagricultural research center in Virginia Beach. Many trees are justnow making their leaf and flower buds for spring. "If people watertheir trees now," Appleton said, "it can have a big effect nextyear."

A couple of inches of mulch can also do a lot to maintain soilmoisture between waterings. But this is not the time to addfertilizer, Appleton said, which can be harmful to leaves and rootsduring periods of water stress.

Trees face a central problem during hot and dry periods: They needcarbon dioxide from the atmosphere to perform energy-capturingphotosynthesis, yet there is no way to let that gas into the plantwithout at the same time losing precious water to the atmosphere.

Gas intake and water loss occur through tiny leaf pores calledstomata. During midday temperature highs, stomata close to minimizewater loss -- putting a crimp in photosynthesis that the plant cantolerate for limited periods. During long days and weeks of extremelyhigh temperatures, however, stomata stay shut to save water, andtrees find themselves in an energy crunch. Photosynthesis slows oreven stops and, gradually, leaves are dropped.

If leaf loss is scattered throughout a tree, it can usually besaved with added water, experts said. But if a tree is losing majorhanks of foliage, especially around the crown, then energy storeshave probably been emptied, and the tree is dying.

Even when water is available, extremely high temperatures can harmtrees directly. The enzymes that facilitate the chemical reactionsthat keep trees alive operate best between 70 degrees and 80 degreesFahrenheit. When temperatures hit the mid-90s, photosynthesis startsto shut down. In the 100-degree range, fatty elements of tree cellmembranes start to "melt," and chlorophyll molecules break down.

At about 115 degrees, enzymatic molecules literally fall apartinside cells, and tree tissues suffer irreparable damage that canspread with each new day of unrelenting heat.

City trees get even hotter than their country counterparts,because solar energy bounces off concrete and brick surfaces asinfrared radiation, adding 9 degrees to 12 degrees to the air wellinto the night. Passing cars and trucks, whose surfaces in summer canexceed 120 degrees, add to the heat load on leaves. And roots, whichwork best at temperatures between 60 degrees and 80 degrees andgenerally stop functioning when soil temperatures exceed 95 degrees,can find themselves roasting, because summer soil temperatures canexceed 100 degrees.

Street cuts to accommodate utility work and road resurfacing takefurther tolls on urban trees by disturbing delicate root hairs. MarkBuscaino, the District's chief forester said that although 4,000streetside trees are being planted annually in Washington, losseshave long been outpacing gains.

A study of Washington tree cover over the 25 years ending in 1997,conducted by American Forests, found that tree canopy had declined byabout 44 percent.

"Every tree out there is a miracle," Buscaino said.

A miracle that this year could use a helping hand.