The West Pontchartrain-Maurepas Swamp IBA is a baldcypress-tupelo swamp surrounding Lake Maurepas in southeastern Louisiana. West Pontchartrain-Maurepas Swamp is one of the largest contiguous tracts of wetland forest remaining in the Lower Mississippi River Alluvial Valley, but levee construction along the Mississippi River has isolated the swamp from spring flood events for almost 200 years. The result is that approximately two-thirds of the swamp is converting to open marsh or open water due to saltwater intrusion in areas adjacent to Lake Maurepas, and nutrient deprivation and/or permanent flooding with stagnant, anoxic water in interior areas of the swamp. In stressed swamp, the overstory is generally sparse, the tops of nearly all tupelo trees have broken off between 3-10m off the ground, overall tree mortality is approximately 2% per year, and no tupelo regeneration has been observed for 15 years. It is expected that 50% of the remaining swamp will convert to open marsh by 2050. A small amount of relatively healthy, closed canopy swamp or bottomland hardwood forest exists on river banks and levees of major canals with slightly higher elevation and some freshwater input. This IBA supports extremely dense breeding populations of Prothonotary Warbler and Northern Parula, even in areas of degraded swamp. This is probably because nesting cavities for Prothonotary Warblers are abundant in senescent tupelo, and nesting sites for Northern Parulas are abundant in Spanish moss on midstory trees. Apparent nest success for both species is high in the West Pontchartrain-Maurepas Swamp IBA, Brown-headed Cowbird parasitism is low in Northern Parula nests and has not been observed in Prothonotary Warbler nests.
This site holds high densities of breeding Prothonotary Warblers, Northern Parulas, and Yellow-throated Warblers. Active rookeries of White Ibis, Great Blue Heron, Great Egret, Little Blue Heron, Tricolored Heron, Green Heron, and Snowy Egret also occur, as do many Bald Eagle nests. Duck species using the swamp include Mallards, Wood Ducks, Gadwall, American Widgeon, Northern Pintail, Northern Shoveler, along with American Coot.
The West Pontchartrain-Maurepas Swamp IBA is threatened by tree mortality primarily caused by saltwater intrusion and/or permanent flooding with stagnant water. Other threats include destruction of regenerating trees by nutria and annual spring defoliation of the dominant tree species by forest tent caterpillars and baldcypress leafrollers. Hurricane Katrina felled much of the midstory in areas adjacent to Lake Maurepas, but more interior areas were relatively undamaged by the storm. Both Prothonotary Warblers and Northern Parulas use midstory trees as nesting substrate. Prothonotary Warblers use natural cavities in senescent tupelo, but tree mortality in stressed swamp is high, and Prothonotary Warbler populations will probably decline with tupelo populations. Northern Parulas use spanish moss as a primary nesting substrate, and any reduction of spanish moss in a hurricane event may impact their populations. Marsh areas are in danger of converting to open water due to saltwater intrusion, flooding and subsidence. Invasive Salvinia molesta may be outcompeting duck weed, and local hunters have noted a dramatic decline in wintering duck populations.
Actual threats, sources of threats, and levels listed
Altered composition/structure - 2
Altered water quality - 1
Herbivory - 7
Modification of water levels; changes in natural flow patterns - 10
Salinity alteration - 10
Toxins/contaminants - 3
Sources of threats:
Channelization of rivers or streams - 10
Construction of ditches, drainages or drainage systems - 10
Development and maintenance of pipelines, roads or utilities - 2
Invasive/alien species - 5
Levee or dike construction - 10
Oil or gas drilling - 5
Saltwater intrusion - 10
Shoreline erosion - 7
The U.S. Army Corps of Engineers owns the Bonnet Carre Spillway Reserve. The State of Louisiana owns Joyce, Manchac, and Maurepas Swamp WMAs. Much of the remainder of this IBA is privately owned.
Forested areas of Maurepas Swamp are approximately 80% swamp and water tupelo and 20% baldcypress. Understory tree species include swamp red maple, green and pumpkin ash, and waxmyrtle. In closed-canopy swamp there is little herbaceous vegetation, but in stressed, open-canopy swamp there is a contiguous layer of herbaceous vegetation dominated by arrow arum, smartweed, and alligator weed. In marsh areas, the plant community varies along a salinity gradient, with Spartina dominating more saline areas, and bulltongue in fresher areas. Common Salvinia is an invasive species in this site that makes the area less suitable for large numbers of waterfowl. Marsh categories include larger proportions of salt and brackish marsh and a smaller proportion of intermediate marsh. Open water was excluded from this site to the extent possible, as it does not support large populations of birds. Most of the area is subject to flooding, especially during easterly winds.
The primary purpose of the Bonnet Carre Spillway Reserve is flood control in the Lower Mississippi Valley. Designed after the 1927 Flood to help with the Mississippi River and Tributaries (MR&T) flood control, it has been opened 9 times since 1937, most recently during the high water year of 2008. During floods, the Mississippi River, through the Spillway, brings fresh water and nutrients into Lake Pontchartrain, improving habitat for some wildlife species and birds. The area is also used for recreational bird-watching.
Most of the land area of the West Pontchartrain-Maurepas Swamp IBA is utilized only during the deer hunting season. Recreational fishing and boating occurs on bayous, canals, rivers and Lake Maurepas, and some commercial fishing and crabbing occurs on rivers and Lake Maurepas and passes to Lake Pontchartrain. Many private camps are located on major rivers and bayous. Alligators are hunted on waterways in fall. Duck hunting has declined with decreasing use of the area by wintering ducks. Access to the swamp areas is mostly limited to pirogues and canoes, but some access on foot is possible in the Maurepas Swamp WMA