When Thoreau patrolled the rivers of Concord, he marveled at the humble button bush, which provided ''one of the wildest features in our scenery.'' What would he say now of the dramatically beautiful purple loosestrife? This invading alien is displacing the native plants and threatening wildlife in Concord's water meadows.
Perhaps he would agree with Cornell University biologist Richard A. Malecki that the habitat destruction isn't worth the floral show.
Malecki says the invader has endangered wildlife habitats over much of the Northeastern and parts of the Midwestern United States. He notes, for example, that the plant has invaded more than 1,000 acres of marshland in the Montezuma National Wildlife Refuge, a 6,000-acre park in central New York State.
That invasion has taken place over the past 31 years, beginning with a few sparse strands of the alien. Something similar has occurred among the water meadows around Concord. Vast splashes of brilliant rose purple now color these wetlands in summer. It is a stunning display unknown to Thoreau. But it doesn't offer the sheltering, nourishing habitat for waterfowl and other wildlife which the native plants provide.
''Invasion of this exotic perennial plant already has resulted in elimination of many native plants species from a number of wetland areas in the Northeast,'' Malecki said in an announcement from Cornell. ''If left unchecked, the detrimental effects of loosestrife encroachment will continue to place additional stress on wildlife resources that are plagued already by the loss of valuable wetland habitats,'' he warned.
Purple loosestrife is a hardy plant that originated in Europe. It thrives in marginally wet areas, such as flood plains and water meadows, which tend to be flooded in the spring and dry out during summer and fall. Its stems make a dense thicket that birds and animals cannot penetrate. Invertebrates on which water birds feed do not survive there.
The plant does provide some benefit besides its beauty. Bees harvest abundant nectar from the blossoms that hang on long panicle spikes. But, in wildlife preservation areas especially, that is poor compensation for lost habitat.
Malecki says intensive research is needed to find an effective way to control the loosestrife pest. Hand weeding, flooding (to drown growing plants), mowing, burning, even chemical weed killers, have been tried. But none of these measures are more than partly successful. Research at Cornell suggests that sowing Japanese millet might provide both wildlife food and competition for the loosestrife during the low-water summer growing period.
Whatever measures may prove effective, it may still be impossible to eradicate the alien plant without destroying the native flora, too. Thus purple loosestrife has become a beautiful pest that wildlife managers must learn to control and live with. It is another example of how an exotic species can upset a long-established ecology.