Flooding disperses invasive plant, fish species

Associated Press Modified: April 29, 2012 at 2:16 pm •  Published: April 29, 2012
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BETHEL, Vt. (AP) — Last year's hurricanes and flooding not only engulfed homes and carried away roads and bridges in hard-hit areas of the country, it dispersed aggressive invasive species as well.

In Vermont, the floodwaters from Tropical Storm Irene and work afterward to dredge rivers and remove debris spread fragments of Japanese knotweed, a plant that threatens to take over flood plains wiped clean by the August storm.

The overflowing Missouri and Mississippi rivers last year launched Asian carp into lakes and oxbows where the fish had not been seen before, from Louisiana to the Iowa Great Lakes. Flooding also increased the population along the Missouri River of purple loosestrife, a plant that suppresses native plants and alters wetlands.

"It's quite an extensive problem around the country and it's spreading," said Dr. Linda Nelson, aquatic invasive species expert with the U.S. Army Corps of Engineers. The agency's budget for controlling invasive aquatic plants has grown from $124 million in 2008 to $135 million for fiscal year 2012.

Dr. Al Cofrancesco, director of the Corps' Invasive Species Center in Vicksburg, Miss., said invasive species are not a problem when they're in their native range.

"There are things that keep them in natural balance. The problem occurs is when we move into areas where they don't have those natural controls or regulators and they expand very rapidly," he said.

In Vermont, floodwaters and repair work broke off portions of stems and woody rhizomes of the aggressive Japanese knotweed. The perennial, imported from Asia as an ornamental, was already a problem in Vermont and a dozen other states in the Northeast, the Pacific Northwest and the Midwest. It spreads quickly on riverbanks, floodplains and roadsides, choking out native plants, degrading habitats of fish, birds and insects and weakening stream banks

"The whole Irene event was ideal" for knotweed, said Brian Colleran, a coordinator for Vermont's knotweed program.

The plant, which resembles bamboo when mature, spreads quickly in disturbed soils. Just this week, new young plants were inching out of the silt on the banks of the Camp Brook, a tributary of the White River, where the land looks like a moonscape since floodwaters washed away trees, rocks and other native plants. Once these invasive plants take over, their root structure and a lack of groundcover and native plants and trees with deeper roots, weakens the stream banks, causing erosion, and flood damage.

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