- The Washington Times - Monday, August 26, 2002

RICHMOND Those things crunching under your feet may make it seem a little like fall.
Some trees are dropping their leaves already, because of the drought.
It's a defense mechanism, explains professor Robert Jones, head of the biology department at Virginia Tech. He says the drought's effect on trees will be apparent for several years to come, well beyond this early shedding.
The leaf-dropping process is called abscission, a normal process by which a plant sheds its leaves, said Mr. Jones. The tree builds a "corky" barrier between the leaf and the stem at the base of the leaf, cutting off the leaf from water. "Eventually, that's the end of the story. The leaf shuts down and dies," Mr. Jones said.
The leaves are sacrificed so the trees can more efficiently use water to store the carbohydrates they need to survive in the long haul, like a long-distance runner who eats or "packs" large amounts of carbohydrates before a race.
A big tree can suck down a lot of water up to 100 gallons a day said Mr. Jones, so it must be efficient to survive. "A green leaf is basically a leaky faucet. They can control water loss a little bit, but they will still lose some water," he said.
Ongoing drought means thirsty trees can't scavenge enough water to remain healthy. Some types of trees are more prone to abscission than others, namely trees that grow new leaves all summer and tend to shed leaves more readily. Mr. Jones said examples are: sycamore, sweet gum, birch and yellow poplar, or tulip trees.
The drought is increasing trees' mortality rates in the Middle Atlantic region, in places such as Virginia, Maryland and the District.
In a typical year, about 1 percent of medium-sized to large trees in a forest die. Severe drought can increase that number to 3 percent, 4 percent or even 5 percent. Mr. Jones has seen higher numbers of dead trees in Virginia forests this year, and he expects to see more in upcoming years.
Those that don't die will be weakened by several years of dry conditions. "Some of the trees that were healthy, they may not die, but this drought will stress them," said Mr. Jones. "If another stress factor comes along, they can't deal with it."
In the short run, the earlier leaf-dropping suggests sad news for those who trek to their favorite scenic spots for fall leaf-watching.
Mr. Jones predicts "less-than-excellent" leaf color this fall especially in particularly parched areas without a lot of rain in September.

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