Mississippi lowland forests

• Category: Forest Biomes.
• Geographic Location: North America.
• Summary: This biodiverse region is threatened by land conversion, but has attracted forces willing to battle to preserve it. The region is home to vast numbers of wintering waterfowl, endangered species like freshwater mussels, and the possibly extinct ivory-billed woodpecker.

The Mississippi Lowland Forest ecoregion—also called the Mississippi Alluvial Valley—encompasses the historic floodplain of the lower Mississippi River that was formed by receding glaciers more than 12,000 years ago. Extending from the southern tip of Illinois to the Gulf of Mexico, a distance of approximately 500 miles (800 kilometers), this region drains nearly 40 percent of the North American continent.

While much reduced, this 43,360-square-mile (112,300-square-kilometer) complex of old-growth forested wetlands interspersed with swamps, cypress-tupelo brakes, shrub-scrub wetlands, and emergent wetlands once provided wetland functions and wildlife values of inestimable worth.

These habitats supported a stunning variety of forest interior species, including the ivory-billed woodpecker (Campephilus principalis), one of the largest woodpeckers known and the biggest ever to inhabit the United States. An intensive search effort has been underway for this species following unconfirmed sightings in eastern Arkansas in 2004 and on the Louisiana-Mississippi border in 2017, but these sightings are unconfirmed, and thus the species has been listed as critically endangered.

Biodiversity

Historically, seasonal flooding was the primary ecosystem driver for the Mississippi Lowland Forest, creating a dynamic patchwork of diverse habitat types that supported a wide variety of plant and animal species. The historical climax plant community (a steady-state community composed of species best adapted to average conditions in that area) consisted of more than seventy species of bottomland hardwood trees, dominated by hard (nuts) and soft (berries) mast-producing trees. These featured several species of oak (e.g., Quercus nuttallii, Q. lyrata, Q. phellos, Q. nigra), hackberry (Celtis occidentalis), and green ash (Fraxinuspennsylvanica). Mast and other foodstuffs produced by these trees provided forage for huge populations of migrating and wintering waterfowl.

Frequency and duration of periodic flooding interacted to determine plant community composition and species distribution. For example, Q. pagoda and Q. phellos tended to occur on higher, less flood-prone sites, while Q. lyrata occurred on low sites that flooded frequently and for longer periods of time. Bald cypress (Taxodium distichum) and tupelo (Nyssa aquatica) dominated the permanently-flooded sloughs.

Throughout the twentieth century, however, elaborate and highly-managed flood control systems were developed to constrain the Mississippi River within a relatively narrow floodplain; natural flooding has been reduced by 50 to 90 percent. As a result, fully 80 percent of the Mississippi Lowland Forest biome has been lost, making the Mississippi Alluvial Valley (MAV) one of the most heavily-converted ecoregions in the United States. What does remain comprises tens of thousands of tiny fragmented patches, fewer than 100 of which are believed to be large enough to support self-sustaining populations of forest-breeding birds and other area-sensitive wildlife. Yet, despite this attrition, a wide variety of animal species, including 40 percent of all North American waterfowl, still utilize this ecoregion for all or part of their life cycle.

Avian and Fish Activity

Mississippi lowland forests currently serve as the continent’s most important wintering habitat for mallard (Anas platyrhynchos) and wood duck (Aix sponsa). Other waterfowl species, such as gadwall (Anas strepera) and green-winged teal (Anas crecca), are also common. Catahoula Lake and the lower Mississippi River delta together also support 10 to 25 percent of the continent’s population of canvasback (Aythya valisineria), the largest concentration of these ducks in the world.

Unfortunately, while the region’s wetlands still support good numbers of waterfowl, habitat loss and fragmentation has impacted feeding areas and forested sites that provide needed isolation for pair bonding and thermal refuges during cold snaps. Ironically, while land conversion has decimated habitats for some species, it has benefited others—such as northern pintail (Anas acuta), green-winged teal, northern shoveler (Anas clypeata), greater white-fronted goose (Anser albifrons), and snow goose (Chen caerulescens), which all respond favorably to open, agricultural habitats.

In addition to waterfowl, Mississippi lowland forests once provided habitat for some of the most diverse and abundant freshwater mussel populations in North America. As a result of alterations in hydrology and increased agricultural sediment loads, many of those species are endangered or extinct.

Moreover, more than ninety species of fish, many of sport or commercial value, are found here. Many of these have life history strategies that are intricately tied to flooding and the natural hydrology of the system. For example, some fish species rely on peak flood flows to stimulate their spawning activities; others use flooded forest as nursery habitat.

Historically, several species of neotropical migrant passerine birds, woodpeckers, and raptors most likely had source populations in the MAV. Though current populations are much reduced and/or restricted in distribution, certain areas still support a diverse resident and migrant avifauna. Species such as the cerulean warbler (Dendroica cerulea) and Swainson’s warbler (Limnothlypis swainsonii) currently persist in a few large, isolated forest remnants. The swallow-tailed kite (Elanoides forficatus), once widespread in the mid-MAV, is now restricted as a breeding bird to the Atchafalaya Delta in the extreme southern portion of the ecoregion. The future of the MAV’s remaining bird populations is uncertain, particularly because the ultimate effects of relatively recent large-scale clearing and resultant fragmentation have not been fully realized.

Mammal Habitats

Like birds, several species of mammals have suffered population declines or extirpation as a result of landscape-scale changes and human encroachment. Panthers (Puma concolor) once ranged throughout the region; remnants of this population still exist in Florida. The once endangered Louisiana black bear (Ursus americanus luteolus) was removed from the list of threatened and endangered species on March 11, 2016, thanks to conservation efforts. This habitat generalist often overwinters in hollow cypress trees, a rare commodity, in or along sloughs. While poorly studied, it is likely that the region supports several species of bats, which also depend on cypress trees for nesting and roosting.

Environmental Conservation

The MAV’s largest and least-spoiled forested tracts generally remain in the wettest areas: the Cache River Wetlands in Illinois, Crowley’s Ridge and Mingo National Wildlife Refuge in Missouri, White River National Wildlife Refuge in Arkansas, and the Atchafalaya Basin and Big Woods Conservation Area in Louisiana. These forests provide important ecosystem services, such as groundwater recharge, flood attenuation, and water quality enhancement through sediment filtration. They also support a high degree of biodiversity, much higher than in corresponding upland forests.

Conservation partnerships between federal, state, and nongovernmental organizations, such as Ducks Unlimited, are working to restore or enhance public lands in the MAV. They are also working to return cultivated private lands to wildland through the application of conservation easements. The possible rediscovery of the ivory-billed woodpecker has led to a larger effort by organizations, hunters, and landowners to conserve and restore the ecosystem. In the meantime, the conservation of large hardwoods—home to the beetles that are a favorite meal of this species—is contributing to the resurgence of other native creatures, such as the Louisiana black bear.

The impact of climate change on these forests has posed additional challenges to such conservation and species protection programs. The alternating impacts of extreme weather patterns, such as higher temperatures and drought juxtaposed by more frequent and intense flooding events due to increased precipitation, have caused damage, disrupted native breeding and spawning schedules, and, in some locations, have facilitated the introduction and spread of nonnative flora and fauna in the region.

Bibliography

Cooperrider, Allen Y., Raymond J. Boyd, and Hanson P. Stuart. Inventory and Monitoring of Wildlife Habitat. U.S. Bureau of Land Management, 1986.

Elliott, A. B., et al. "Conservation–Protection of Forests for Wildlife in the Mississippi Alluvial Valley." Forests, vol. 11, no. 1, 2020, p. 75. doi.org/10.3390/f11010075. Accessed 8 Nov. 2024.

Gardiner, Emile S. “Outlook for Mississippi Alluvial Valley Forests.” Southern Forest Futures Project, 2015. United States Department of Agriculture, www.srs.fs.usda.gov/pubs/gtr/gtr‗srs201.pdf. Accessed 8 Nov. 2024.

“Louisiana Black Bear.” Bear Conservation, 20 Feb. 2021, www.bearconservation.org.uk/louisiana-black-bear/. Accessed 8 Nov. 2024.

“Lower Mississippi Alluvial Valley.” National Fish and Wildlife Foundation, www.nfwf.org/landscapes/lower-mississippi-alluvial-valley. Accessed 8 Nov. 2024.

“Mississippi Alluvial Valley—Level I Ducks Unlimited Conservation Priority Area, the Most Significant Winter Habitat Area for Mallards in North America.” Ducks Unlimited, www.ducks.org/conservation/where-ducks-unlimited-works/mississippi-alluvial-valle. Accessed 8 Nov. 2024.

Noss, Reed. “Mississippi Lowland Forests.” One Earth, www.oneearth.org/ecoregions/mississippi-lowland-forests/. Accessed 8 Nov. 2024.

Schwartz, Charles W. and Elizabeth R. Schwartz. The Wild Mammals of Missouri, 2nd rev. ed. University of Missouri Press, 2001.