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Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands


After more than 50 years of study and debate, purple loosestrife (Lythrum salicaria), an emergent aquatic plant, has come to the forefront in marsh management discussions in the eastern and midwestern United States. The relatively recent and rapid westward expansion of the plant and its rise to dominance in many inland marsh and river systems are causes for alarm among botanists, wetland ecologists, and waterfowl managers. With nearly 190,000 hectares of wetlands being lost annually in the conterminous United States, it is imperative that the remaining habitat realize its optimum productivity. Unfortunately, purple loosestrife's strong competition with and replacement of other, more desirable aquatic emergents has led to a decline in wildlife food and cover values in many wetlands.

This report documents the spread and impacts of purple loosestrife in North America. It details the authors' research and personal observations and synthesizes a vast body of literature on L. salicaria. The publication should serve many purposes. First and foremost, it will be a valuable source book for all biologists interested in loosestrife ecology. It should also encourage additional research to find acceptable and effective ways of controlling purple loosestrife. Finally, the report will be of practical use to wetland managers facing the threat of loosestrife invasion.

In addition to being a comprehensive treatise on the accumulated body of knowledge on purple loosestrife, this publication serves to illustrate two fascinating phenomena. The first is the degree to which certain species can adapt to and colonize new environments. L. salicaria owes much of its rapid spread across North America to its wide tolerance of varying physical and chemical conditions, such as those characterizing disturbed habitats. The species also is a prolific seed producer and uses many mechanisms for seed dispersal. Second, the story told herein emphasizes how much we can impact our environment. L. salicaria seeds originally reached North America in the cargo and ballast of ships coming from Europe. Rootstalks may also have been brought in by horticulturists. The plant subsequently spread to interior wetlands by way of canals, irrigation ditches, and roads. Its use in horticulture and beekeeping industries has also expanded the range of the species. Thus, human activities, combined with loosestrife's physiological and ecological adaptability have led to its present day distribution in North America.

As a wildlife resource professional, I am concerned about the growing evidence that waterfowl, furbearers, and other wetland-dependent species are being adversely impacted by loosestrife. The resulting biological, recreational, and economic repercussions are disturbing; however, the authors offer hope. They review methods that can be applied locally by wetland managers to minimize the expansion of L. salicaria and to cope with existing infestations. Some States have designated the plant a noxious weed. Convincing arguments are also made for the development and implementation of a biological control program to address the loosestrife invasion. The favorable cost-benefit ratio presented provides food for thought. Clearly, a long-term solution is needed if this major ecological problem is to be halted. The suggested increased emphasis on research on biological control methods should receive immediate attention by concerned natural resource agencies.

Harvey K. Nelson
Regional Director
U.S. Fish and Wildlife Service
Minneapolis, Minnesota

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