Why juniper trees can live on less water( DURHAM N.C. -- An ability to avoid t...)

DURHAM, N.C. -- An ability to avoid the plant equivalent of vapor lock and a favorable evolutionary history may explain the unusual drought resistance of junipers, some varieties of which are now spreading rapidly in water-starved regions of the western United States, a Duke University study has found.

"The take-home message is that junipers are the most drought-resistant group that has ever been studied," said Robert Jackson, a professor of global environmental change and biology at Duke's Nicholas School of the Environment and Earth Sciences.

"We examined 14 species from the U.S. and Caribbean, and they're all relatively drought-resistant -- even ones in the mountains of Jamaica that get hundreds of inches of rain a year," he said.

"They've been expanding for about 100 years in some places, and drought plays a role in that," added Jackson, who is corresponding author of the new report published Feb. 27 in the American Journal of Botany's online edition. "For example, recent droughts have decimated pinyon pine populations in pinyon-juniper woodlands of the Southwestern U.S. but left the junipers relatively unscathed."

Many juniper species -- including several popularly known as cedars -- "are invading drier habitats and increasing in abundance where they already exist by surviving droughts that other conifers cannot," the report said.

The work was funded by the National Science Foundation, Duke University and the Andrew W. Mellon Foundation.

To understand why junipers are so successful, Jackson's graduate student Cynthia Willson and Duke associate biology professor Paul Manos assessed structural and genetic features in the 14 species that can explain their special drought tolerance.

They found a key structural adaptation in junipers: resistance to what scientists call "cavitation" -- a tendency for bubbles to form in the water-conducting xylem tissues of plants.

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