Mississippi Alluvial Valley – More Information

Background information on the Mississippi Alluvial Valley region, a DU conservation priority area

The Mississippi Alluvial Valley (Region 21*) is the historic floodplain of the Mississippi River formed by melt water as glaciers receded approximately 12,000 years ago. The MAV is approximately 800 km long and covers portions of 7 states from southern Illinois to Louisiana.

The most recent climax plant community in the MAV consisted of approximately 10 million ha of bottomland hardwood forest dominated by hard and soft mast-producing trees including several species of oak (e.g., Nuttall, overcup, willow, water, etc.), hackberry, and green ash. Over 70 species of trees occur in the region. Elevation interacts with hydrology, especially the frequency, duration, and periodicity of flooding, to determine plant community composition and species distribution (Fredrickson 1978, Larson et al. 1981, Reinecke et al. 1989). For example, cherrybark and willow oaks occur on higher, less flood-prone sites, while overcup oak occurs on low sites that flood frequently and for long duration. Cypress and tupelo dominate permanently flooded sloughs (Reinecke et al. 1989).

Flooding in the MAV historically was driven by winter and spring precipitation. Winter rains in combination with greatly reduced plant evapotranspiration resulting from winter dormancy, typically resulted in winter flooding that made mast and other foods available to migrating and wintering waterfowl. Annual variation in duration and extent of flooding likely was great, but inundation of much of the MAV probably occurred each winter (Heitmeyer and Fredrickson 1981).

The landscape in the MAV has changed dramatically during the last 200 years, with the most rapid change occurring within the last 75 years. Today, only about 2 million ha or 20% of the original forest remains in the MAV, the rest having been converted to agricultural production. Initially higher elevation areas were cleared and placed into agriculture. However, even these relatively high sites were prone to flooding, which led to attempts to more or less successfully control hydrological events that sustained and were the very basis for development of this system. Flood control projects have reduced the extent of flooding in some parts of the MAV by as much as 88%, while simultaneously altering the ecologically important effects of flood periodicity, duration, and frequency (Reinecke et al. 1989).

* Region 21 - NABCI Bird Conservation Region 26

Importance to waterfowl

As a consequence of alteration of hydrology and conversion of forest to agriculture, the current landscape in the MAV is highly fragmented and much drier than in historical times. It is dominated by agricultural land, some of which provides significant waterfowl habitat via flooding of waste grain, particularly rice and soybeans.

No data exist to estimate historical populations of migrating or wintering waterfowl in the MAV. Suffice to say that reliable winter flooding and abundant food resources in most years combined to make the MAV one of the most continentally significant areas of winter and migration habitat for several species, particularly mallards, wood ducks, gadwall, green-winged teal, American wigeon, and hooded mergansers (Reinecke et al. 1989). Reinecke et al. (1992) used aerial transects to estimate at least 1.1-1.8 million mallards, or approximately 17-29% of the breeding population, wintered in the MAV during winters of 1987-88 and 1988-89. However, these data were collected when mallards and many other species of ducks were at historically low population levels resulting from extended drought on prairie breeding areas in the 1980s (Reynolds 1987).

In 1999, the mid-continent mallard breeding population was estimated at 10.8 million, a 41-48% increase from the late 1980s (Wilkins and Cooch 1999). Applying that increase to the estimates derived by Reinecke et al. (1992) suggests that perhaps 1.6-2.7 million mallards wintered in the MAV in 1998. There are no other statistically valid surveys performed to estimate winter populations of mallards or other species in the MAV. However, harvest of mallards from the MAV states, including TN, KY, AR, MS, LA (including portions of those states outside of the MAV) during 1998 was estimated at 1.68 million. Assuming a very high harvest rate of 0.25 (which should lead to a conservative population estimate), as many as 4-5 million mallards may have wintered in this region. Hence, based upon past surveys, estimated breeding populations, and estimated harvest, it seems reasonable to conclude that at least 1.1 and perhaps <4 million mallards may winter in the MAV in some years, representing 17-40% of the estimated 1999 mid-continent breeding population. Clearly, the MAV is the most important wintering area for mallards in North America. Further, Nichols et al. (1983) suggested that the overall importance of the MAV to wintering mallards increases with winter severity and in wetter than average winters when habitat conditions are best.

The MAV is also a continentally important area for breeding and wintering wood ducks (Bellrose and Holm 1994), and following widespread conversion of forested wetlands to agriculture, has become more significant to northern pintails, green-winged teal, and northern shovelers, as well as snow and white-fronted geese. Catahoula Lake, a 12,150 ha basin that lies within the MAV, provides habitat to peak populations of 400,000 ducks. Catahoula Lake is particularly important to early migrant blue-winged teal and northern pintails, with September/October concentrations of 150,000-300,000 occurring in most years. Additionally, it has wintered up to 128,000 canvasbacks, which is the largest concentration in the world (LDWF unpublished data). Catahoula Lake and the Lower Mississippi River Delta (Gulf Coast Conservation Region) combined winter 10-25% of the continental population of canvasbacks.

Overall, the MAV is most important as migration and winter habitat, but it is also a primary breeding area for wood ducks. The primary limiting factor for populations of migrating and wintering waterfowl is assumed to be foraging habitat. Ducks Unlimited, in an effort to continually refine conservation programs through adaptive management, set about assessing the amount of foraging habitat potentially available to waterfowl in the MAV. In addition, during the course of this effort, DU also collected information on within and among year variation in winter habitat conditions in the MAV. This is complex evaluation effort was initiated in 1997 and remains a work in progress. However, information gained to date from this study as well as others recently completed by other researchers have allowed DU to refine conservation programs.

Following are some conclusions based upon data gathered from 1997 through the winter of 2003-2004:

  1. The absolute quantity of potential foraging habitat and associated estimates of duck-use-days provided are in excess of what is required by LMVJV population objectives in all but the driest of winters in the MAV.
  2. The bulk of the foraging habitat in the MAV consists of privately managed harvested agricultural habitat.
  3. Natural flooding of cleared agricultural land and forested wetlands remain a vital, viable component of the winter habitat complex in the MAV, and in most years, provides substantial potential foraging habitat.
  4. There remain questions about foraging habitat quality, the role of refuges and the need for additional refuges in the MAV to enable birds to maximize use of potential foraging habitat.

While foraging habitat currently does not appear to limit the population of birds wintering in the MAV, it should be noted that the bulk of foraging habitat has no long-term protection. Indeed, much of the potential foraging habitat in the MAV is agricultural in nature and subject to the whims of changes in agricultural policy, agribusiness and other factors. However, given the current estimated level of foraging habitat in excess of that needed to support desired populations, an opportunity exists to shift the emphasis of conservation programs, as discussed below, from short term effort aimed at adding to the foraging habitat based, to long-term efforts aimed at protecting and securing the foraging habitat based indefinitely.

Importance to other wildlife

The forested wetland habitat that occurred in the MAV provided substantial habitat for a unique array of wildlife. Rivers in the MAV at one time provided habitat for some of the most diverse, abundant freshwater mussel populations on the continent (Christian 1995). Today, due to alterations in hydrology and increased sediment loads from agricultural lands, several mussel species in the MAV are endangered or have become extirpated or extinct. The complex of forested wetlands, sloughs and rivers supports over 60 species of fish, many of which have sport or commercial value (Hoover and Kilgore 1997). The life histories of many species are intricately related to the natural hydrology of the system. For example, some species key on peak riverine flood flows to stimulate spawning activities, whereas others use flooded forest as nursery habitat. Timing and duration of winter and spring flooding are important influences on fish population dynamics (Hoover and Kilgore 1997).

The forests of the MAV also supported a diverse resident and migrant avifauna in addition to waterfowl. Several species of neotropical migrant passerines, woodpeckers, and raptors likely had population centers, or source areas, centered in the MAV. Among these were many area-sensitive species that likely were common to abundant in the pre-agricultural MAV. For example, species such as the cerulean warbler and Swainson's warbler likely occupied much of the northern and entire MAV respectively, whereas currently they exist only in a few isolated, large remnants of forest (Hunter et al. 1992). The ivory-billed woodpecker and Carolina parakeet, once likely residents of much of the MAV, are extinct. The swallow-tailed kite, an area-sensitive raptor that once occurred well into the mid-MAV, now is restricted as a breeding bird to the Atchafalaya Delta in the extreme southern portion of the MAV. The future of these remaining populations is uncertain, particularly because the ultimate effects of relatively recent large-scale clearing and resultant fragmentation are not completely clear or immediate (Faaborg et al. 1992).

As with birds, several species of mammals have suffered population declines or extirpation as a result of landscape-scale changes to the forest of the MAV. The panther has been extirpated from the MAV for several decades. The Louisiana black bear, a subspecies of the American black bear, is a federally listed endangered species whose decline is directly linked to deforestation and fragmentation. The future of this subspecies may well depend on our ability to reforest and reduce fragmentation within its range (Black Bear Conservation Committee 1992). Forested wetlands in the MAV also provide habitat for at least 7 species of bats. Bat populations have never been monitored, but some species in the MAV appear to rely extensively upon large, hollow cypress trees for nursery habitat, and some may be area sensitive. Bats appear to share their requirement for such trees with black bears. It is very likely that bat populations in the MAV were negatively affected by conversion of forest to agriculture, though to what degree remains unknown.

Conservation programs

DU, via the SRO, and in cooperation with many state and federal agencies, private corporations, and private landowners, offers a full range of conservation programs in the MAV. Nearly all of DU's accomplishments in the MAV have been through partnerships with other conservation interests, but DU is a leading partner in delivery of many of these programs. DU has a full staff of biologists, RS/GIS analysts, and engineers that work in tandem on a variety of wetland restoration, enhancement, development, protection and evaluation and monitoring projects.

DU will shift toward conservation programs that emphasize long-term protection of flooded native emergent vegetation and forested wetlands. DU will continue to emphasize work with the USFWS, USFS, and all state agencies in the region to develop, restore or enhance wetlands on public land that will provide foraging habitat in perpetuity. The conservation easement program will be expanded and targeted to emphasize protection in perpetuity of existing tracts of forested wetland and other valuable foraging habitats that flood naturally. Finally, DU has formed a partnership with the USDA NRCS to deliver a large percentage of the WRP in the MAV. WRP is uniquely suited to the MAV with its emphasis on restoration of marginal farmland via reforestation with mast producing hardwood trees, and some restoration of hydrology. The majority of work completed under WRP provides foraging habitat for waterfowl that is protected via perpetual conservation easements.

Through FY2004, DU has conserved 242,504 ha of habitat in the area loosely defined as the MAV (i.e., generally the area identified by the NAWMP). DU conservation programs are an integral part of the NAWMP LMVJV goals, which call for plan partners to provide at least 376,514 ha of foraging habitat for wintering waterfowl (Loesch et al. 1994). Notably, the LMVJV plan only accounts for foraging habitat needs for winter defined as the 90-day period from December 1 through February 28 (Loesch et al. 1994). Considerable numbers of waterfowl occur in migration before and after these periods, consequently LMVJV goals may be conservative.

DU conservation programs in the MAV are delivered at the landscape scale. Currently, opportunities exceed funding and staffing capability. As such, programs are not specifically targeted to any particular area of the MAV. Staff at the SRO developed a specific action plan targeting areas for proactive conservation work in the MAV over through fiscal year 2008. The action plans calls for continued restoration work through the Wetland Reserve Programs and other programs that both restore and provide perpetual protection to habitat, increased emphasis on securing conservation easements, and increased extension efforts aimed at encouraging land use and agricultural practices that are wildlife and waterfowl friendly. Toward this end, the SRO has developed a marketing initiative entitled River CARE to publicize conservation programs and assist with fundraising efforts to support conservation programs.

Goals

The primary goal of DU conservation programs in the MAV will be to protect, restore, enhance, and manage wetlands and waterfowl habitat in the MAV consistent with the objectives of the LMVJV and River CARE. Specific goals include:

  • Maintain 242,504 ha conserved in the MAV prior to June 30, 2004, including 161,222 ha protected and 81,282 ha restored or enhanced.
  • Make a deliberate shift in emphasis of private lands programs toward extension work with agricultural producers.
  • Expand the existing conservation easement program and develop focus areas for the entire MAV, with a goal of protecting a minimum of 6,000 ha/yr through FY2008.
  • Restore or enhance at least 14,164 ha of public land that offers habitat benefits in perpetuity, in cooperation with state and federal agencies through FY2008.
  • Encourage active management on a minimum of 40,000 ha/yr through extension and technical assistance efforts.

Assumptions

  • The availability of foraging habitat during the wintering period can limit waterfowl population survival and recruitment rates as mediated through body condition, behavior, and mobility.

Strategies

  • Protect private lands through by expanding the existing conservation easement program through developing focus areas for the entire MAV.
  • Emphasize extension efforts to assist landowners to restore or enhance private land through partners programs and, and to encourage active management of habitat on private lands.
  • Restore or enhance public land in cooperation with state and federal agencies.
    Maintain and expand existing partnerships, while simultaneously exploring and developing additional partnerships that are consistent with the DU mission.