The Fine Art of Flooding Bottomland Forest
Posted: Mon Jan 31, 2011 11:49 am
The Fine Art of Flooding Bottomland Forests
By Larry Williams
http://www.fws.gov/refuges/RefugeUpdate ... b_2011.pdf
Green tree reservoirs (GTRs) are common on national wildlife refuges, especially in the Southeast. Many were constructed in the 1900s to boost habitat for migrating ducks. Creating one usually involved building a levee to impound water on a bottomland hardwood forest and devising a way to deliver and remove water as needed. The result was expansive bottomland forest that could be deliberately flooded with shallow water to allow ducks to reach acorns and other foods produced by the trees.
GTRs were designed to mimic the natural floods that occurred in forests along river floodplains. In today’s fragmented landscapes, it would be impossible for refuges to sustain waterfowl populations without GTRs. Unfortunately, wildlife managers, like most people, can be guilty of too much enthusiasm. Early in the evolution of GTRs, we in the National Wildlife Refuge System tried to keep them flooded as long as possible to maximize habitat for ducks. We typically flooded them in late fall, as ducks arrived, and didn’t drain them until ducks left in spring. Our thinking was: If flooding the forest for a month is good, flooding it for four months must be great.
But, around 1980, watchful staff and long-term monitoring concluded that forests flooded too deep and too long begin to change in unhealthy ways.They stop regenerating because seeds can’t germinate in flooded soil and young trees can’t establish themselves. Existing trees show signs of stress: dead limbs, swollen trunks and small “epicormic” branches that develop on a tree’s trunk when it is stressed and needs photosynthesis capacity. Over a span of years, the species composition changes; important red oak species, such as cherrybark oak and willow oak, are replaced by flood-tolerant species like overcup oak and water hickory.
Felsenthal Pool
Felsenthal National Wildlife Refuge in southern Arkansas has one of the world’s largest GTRs. Its 15,000-acre Felsenthal Pool is surrounded by hardwood forest. With flooding, the pool can expand to 36,000 acres, creating vast habitat for wintering
mallards. By 2000, most refuges, wary of too much flooding, were already managing GTRs with healthy varied flood regimes. But Felsenthal Pool was a special case. The pool’s sheer size, the community’s interest in it and shared jurisdiction with the U.S. Army Corps of Engineers made any change to the flooding regime a challenge.
“It Got Pretty Rough”
When refuge manager Bernie Petersen arrived in 2007, he knew of these conflicts. “It got pretty rough,” he says. “I had several Congressional inquiries and lots of angry phone calls.” The pool’s trees were stressed, and the refuge forester saw a shift in forest composition, but citizens, especially waterfowl hunters, feared that not flooding the GTR, even for one year, would forever
change waterfowl use. The refuge and partners had to convince the public that less flooding was better.
They brought in experts from the U.S. Forest Service, Arkansas Game and Fish Commission, U.S. Geological Survey (USGS) and the Fish and Wildlife Service’s Migratory Birds program. All agreed that sustained flooding was hurting the pool’s habitat value. They
talked to hunters, citizens, county officials and Congressional staff, and they held tours to show stressed trees and lack of forest regeneration.
This education effort enabled the refuge, in cooperation with the Corps — which has jurisdiction for pool water levels — to experiment with less-frequent flooding. The experiments began in the winter of 2007-08. The results are looking good. Tree health is improving and waterfowl hunting has not suffered. The refuge, the USGS and the Corps are working on a long-term plan to alternate flooding with periods of dryness in a way that mimics weather cycles. Once again, we find ourselves returning to where Mother Nature started.
Larry Williams is chief of the
Refuge System’s Division of Budget,
Performance and Workforce.
By Larry Williams
http://www.fws.gov/refuges/RefugeUpdate ... b_2011.pdf
- Wildlife managers have learned that flooding too deep and for too long begins to change bottomland hardwood forests in unhealthy ways. (USFWS)
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GTRs were designed to mimic the natural floods that occurred in forests along river floodplains. In today’s fragmented landscapes, it would be impossible for refuges to sustain waterfowl populations without GTRs. Unfortunately, wildlife managers, like most people, can be guilty of too much enthusiasm. Early in the evolution of GTRs, we in the National Wildlife Refuge System tried to keep them flooded as long as possible to maximize habitat for ducks. We typically flooded them in late fall, as ducks arrived, and didn’t drain them until ducks left in spring. Our thinking was: If flooding the forest for a month is good, flooding it for four months must be great.
But, around 1980, watchful staff and long-term monitoring concluded that forests flooded too deep and too long begin to change in unhealthy ways.They stop regenerating because seeds can’t germinate in flooded soil and young trees can’t establish themselves. Existing trees show signs of stress: dead limbs, swollen trunks and small “epicormic” branches that develop on a tree’s trunk when it is stressed and needs photosynthesis capacity. Over a span of years, the species composition changes; important red oak species, such as cherrybark oak and willow oak, are replaced by flood-tolerant species like overcup oak and water hickory.
Felsenthal Pool
Felsenthal National Wildlife Refuge in southern Arkansas has one of the world’s largest GTRs. Its 15,000-acre Felsenthal Pool is surrounded by hardwood forest. With flooding, the pool can expand to 36,000 acres, creating vast habitat for wintering
mallards. By 2000, most refuges, wary of too much flooding, were already managing GTRs with healthy varied flood regimes. But Felsenthal Pool was a special case. The pool’s sheer size, the community’s interest in it and shared jurisdiction with the U.S. Army Corps of Engineers made any change to the flooding regime a challenge.
“It Got Pretty Rough”
When refuge manager Bernie Petersen arrived in 2007, he knew of these conflicts. “It got pretty rough,” he says. “I had several Congressional inquiries and lots of angry phone calls.” The pool’s trees were stressed, and the refuge forester saw a shift in forest composition, but citizens, especially waterfowl hunters, feared that not flooding the GTR, even for one year, would forever
change waterfowl use. The refuge and partners had to convince the public that less flooding was better.
They brought in experts from the U.S. Forest Service, Arkansas Game and Fish Commission, U.S. Geological Survey (USGS) and the Fish and Wildlife Service’s Migratory Birds program. All agreed that sustained flooding was hurting the pool’s habitat value. They
talked to hunters, citizens, county officials and Congressional staff, and they held tours to show stressed trees and lack of forest regeneration.
This education effort enabled the refuge, in cooperation with the Corps — which has jurisdiction for pool water levels — to experiment with less-frequent flooding. The experiments began in the winter of 2007-08. The results are looking good. Tree health is improving and waterfowl hunting has not suffered. The refuge, the USGS and the Corps are working on a long-term plan to alternate flooding with periods of dryness in a way that mimics weather cycles. Once again, we find ourselves returning to where Mother Nature started.
Larry Williams is chief of the
Refuge System’s Division of Budget,
Performance and Workforce.