Atchafalaya Basin altered by man, nature
By RICK BOGREN
BATON ROUGE — Man-made modifications in the Mississippi River Valley — levees, cut-offs and dams — have all caused changes in the ecology of the Atchafalaya Basin and similar areas, Wes Cochran, a graduate student in the School of Renewable Natural Resources, told a conference audience recently.
Those and effects of natural and man-made disasters and disruptions were featured as scientists presented results of some of their research at the fourth Louisiana Natural Resources Symposium Aug. 1 to 2 on the LSU campus in Baton Rouge.
The fourth in a series of biannual conferences was presented by the LSU AgCenter School of Renewable Natural Resources.
“The conference is focused on the effects of human and natural changes on forested and wetland ecosystems and wildlife,” said Todd Shupe, of the AgCenter’s Louisiana Forest Products Development Center and one of the organizers of the event.
The move from riverine flooding to rain-dominated flooding has disrupted the basic ecology of the remaining fragments of bottomland hardwood ecosystems, Cochran said.
The changes constrict and isolate floodplain habitat, causing less flooding “with longer, deeper floods in some areas and cessation of floods in others,” Cochran said. The results include a region-wide shift in vegetation composition with more shade-tolerant and flood tolerant species.
Urban neighborhoods moving into rural areas are another demonstration of human-induced disturbances that affect ecosystems through the Gulf Coast states, said Francisco Escobedo, of the University of Florida at Gainesville.
“What happens is forest systems — working forests — become urban and lose their ‘ecosystem services’ that include carbon storage, timber availability and water quality and quantity,” Escobedo said.
Similar to other disturbances, urbanization can alter ecosystem structure and function, he said.
Another example of “man-made” problems is the growth of feral hog populations, said Kim Marie Tolson, of the University of Louisiana-Monroe.
“Hogs are a human-induced disaster on our landscape,” Tolson said. “They have the highest reproductive potential of any large mammal in North America.”
The feral hog is the No. 2 game animal harvested in the United States — second only to white-tail deer — and can tolerate a wide range of habitat types and climates, she said.
Tolson’s research focuses on feral hog reproduction in Louisiana. “Their proclivity to reproduce combined with their omnivorous diet has led to many problems for the forest and agriculture industries.”
Nonhuman-caused disasters include floods and hurricanes, and hurricanes can have a substantial influence on freshwater fisheries, said LSU AgCenter researcher Michael Kaller.
“Hurricanes are somehow changing the biogeographic habitats of these systems,” Kaller said. Louisiana freshwater fisheries had fewer fish following hurricanes Katrina and Rita because of changes in water quality.
In addition, the opening of the Morganza Floodway in 2011 had a profound effect on fish. “After the Morganza flooding, the slate was wiped clean,” Kaller said. “This is a different Atchafalaya Basin.”
Fish were negatively affected, primarily through a loss of diversity, including recreationally and economically important species, he said. Changes to habitat may be a far greater source of long-term mortality and may impede recovery.
“Although hurricanes are natural phenomena in coastal landscapes, their intensity and frequency can exceed the ability of freshwater resources to respond,” Kaller said.
Along with creating problems with fisheries, hurricanes also can disrupt many different forms of wildlife.
Scott Durham, of the Louisiana Department of Wildlife and Fisheries, described how Hurricane Isaac affected deer populations in 2012.
“White-tail deer were especially affected in unprotected regions of St. Bernard and Plaquemines parishes,” he said. “Additional significant flooding occurred in the marshes and swamps adjacent to lakes Pontchartrain and Maurepas, where wind-driven water depths were estimated at over 5 feet above normal in some areas.”
About 90 percent of the season’s fawns were lost along with moderate adult mortality, Durham said.
After the flood, however, came a new period of “green-up” — like spring, Durham said. This provided the surviving deer “a high period of nutritional availability.”
“Most coastal regions are adapted to floods, and habitats recover,” he said. “However, subsidence and other contributing factors in coastal decline appear to make these regions and associated wildlife more and more vulnerable.”