U.S. scientists, part of an international research team, say hardwood trees are being harmed by an invasive weed spreading across the nation.
The weed harms native maples, ashes and other hardwood trees by releasing chemicals that kill a soil fungus the trees depend on for growth and survival.
The tree-stifling alien, garlic mustard -- Alliaria petiolata -- was first introduced into the eastern United States in the 1860s. It since has spread into Canada and 30 states in the East and Midwest, with recent sightings as far west as Oregon.
While many mechanisms have been proposed to explain the success of invasive species, the new study is the first to determine an invasive plant harms native plants by thwarting the biological "friends" upon which they depend for growth.
The study was conducted by researchers at Harvard University, the University of Guelph, the University of Montana, Purdue University, and the UFZ Center for Environmental Research in Germany.
The research appears in the current issue of the Public Library of Science.
Copyright 2006 by United Press International
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