CAMBRIDGE, Mass. -- An invasive weed that has spread across much of the U.S. harms native maples, ashes, and other hardwood trees by releasing chemicals harmful to a soil fungus the trees depend on for growth and survival, scientists report this week in the Public Library of Science. The tree-stifling alien, garlic mustard (Alliaria petiolata), first introduced into the U.S. in the 1860s, has since spread to Canada and 30 states in the East and Midwest, with recent sightings as far west as Oregon.

While many mechanisms -- from the absence of natural predators or parasites to the disruption of long-established interactions among native organisms -- have been proposed to explain the success of invasive species, this new work is the first to show that an invasive plant harms native plants by thwarting the biological "friends" upon which they depend for growth. The work, which provides striking evidence for a unique process by which invaders harm native species, was conducted by researchers at Harvard University, the University of Guelph, the University of Montana, Purdue University, and the UFZ Centre for Environmental Research in Germany.

"While vanishing habitat caused by human activity is the number one threat to biodiversity, there is great concern over the impact of accidental and intentional dispersal of alien invasive species across the globe," says Kristina A. Stinson, a plant population biologist at the Harvard Forest, Harvard's ecology and conservation center in Petersham, Mass. "In North America, thousands of nonnative plants and animals have become established since European settlement and many more continue to be introduced. Some alien species cause little harm, while others can become very aggressive and radically transfigure their new habitat.

"The mechanisms for this phenomenon and its potential long term impacts remain poorly understood," Stinson adds, "but one possibility is that invasive species may disrupt fragile ecological
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Contact: Steve Bradt
steve_bradt@harvard.edu
617-496-8070
Harvard University
25-Apr-2006

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