Albuquerque, N.M. -- Just as you can't judge a book by its cover, you probably can't judge a tree's drought tolerance by its leaf response, according to Penn State researchers.

"It appears that leaf physiology is not the only way to look at the drought tolerance of trees," says Dr. Marc Abrams, professor of forest ecology in the College of Agricultural Sciences.

Conventional measures of drought tolerance in trees include adaptations deemed necessary to conserve or withstand an absence of water, including deep roots and thick leaves that can continue to photosynthesize -- convert sunlight into usable energy. Drought intolerant species tend to have shallow roots and shut down during drought. It is not unusual for drought-intolerant species to drop their leaves in time of drought and stop photosynthesizing.

The researchers decided to look at another measure of a tree's drought response, the amount of energy put into trunk growth.

"It appears that the drought tolerance ranking of trees in Central Pennsylvania based on ecological distribution or leaf physiology during drought is not an indication of a tree's growth response during drought," the researchers told attendees at the Ecological Society of American Conference, today (Aug. 14) in Albuquerque. "When we looked at the tree rings for drought years, some trees that are considered intolerant to drought, had average or above average growth."

The researchers, who include Abrams; Charles M. Ruffner, graduate student in forest resources; and T. A. Morgan, undergraduate in forestry resources, looked at trees growing in four different areas in the ridge and valley province of Pennsylvania -- ridge, valley, barren and riparian.

The ridge tops were the driest areas and the riparian areas near rivers and streams were the wettest. The valley makes up a moist intermediate soil climate and the barrens are
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Contact: A'ndrea Elyse Messer
aem1@psu.edu
814-865-9481
Penn State
14-Aug-1997