Project 2.001 – Systems . Illustrate

Posted on March 13, 2011

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http://prezi.com/thbig411jqn9/mississippi-river-riparian-vegetation-and-batture-ecologies/

Mississippi River Riparian Vegetation and Batture Ecologies

The Lower Mississippi River Alluvial Plain is one of the most dynamic ecoregions in the world. The Mississippi river drains all or part of 31 states and two Canadian Provinces. The watershed is bordered in the North by Canada, on the east by the Appalachian Mountains, and on the West by the Rocky Mountains. The broad, flat Alluvial Plain begins at the confluence of the Ohio and Mississippi Rivers in Cairo, IL and continues to the Gulf of Mexico, with river terraces and levees providing the main elements of flood relief. This ecoregion provides important habitat for fish and wildlife and includes the largest continuous system of wetlands in North America. Soils tend to be poorly drained, except for isolated areas of sandy soils.

Bottomland deciduous forest vegetation used to cover most of the region before nearly 80% was cleared and drained for cultivation. Most of the northern and central sections of the region are in agricultural cropland and receive heavy amounts of pesticide, herbicide and fertilizer runoff.

The large drainage network of the Mississippi causes high amounts of suspended sediment, particularly towards the southern end of the river. This sediment is accreted against the levees, and stabilized by pioneer vegetation, which creates the land known as the batture. This area between the levees on either side of the river extends virtually the entire length of the alluvial plain along the course of the Mississippi River and its major tributaries, and on its main distributary, the Atchafalaya River. The levees have separated much of the river and its immediate habitat from the rest of the hydrologic system. In addition, large river channel dredging projects remove silt and sediment accumulations from the river channel to facilitate navigation along the Mississippi River. The levee system, dredging projects and the large concrete river revetments (installed by the US Army Corps of Engineers for flood protection) have all contributed to the decrease of sediment mobilization within the system, thus altering the delta formation at the mouth of the river and contributing to the loss of habitat for many coastal and estuarine species. [Chappman, et al]

The batture then, is a unique ecosystem, which would not exist without man-made levees, but still provides valuable wildlife habitat area for resident and migratory species.

Definitions of Batture

The earliest recorded origins of the batture can be traced back to the first French and Spanish settlers who built levees in the area around New Orleans. When sediment accreted on the riverside of the levee, merchants, politicians and property owners went to court to settle ownership rights to the land. In 1805, the courts of Louisiana ruled that lands developing on the other side of levees would be the rightful lands of the adjacent property owners and not the public property of Louisiana. These lands would come to be called “batture” from the French, meaning the land “beaten” by the river.

The Legal Definition of a batture still holds today as “an elevation of the bed of a river under the surface of the water; but it is sometimes used to signify the same elevation when it has risen above the surface. The term battures is applied, principally, to certain portions of the bed of the river Mississippi, which are left dry when the water is low, and are covered again, either in whole or in part by the annual swells.” [Bouvier’s Law Dictionary, 1856 Edition]

Louisiana Department of Wildlife and Fisheries considers the batture ecologies to be a major natural community type, and it is defined as the community that “develops on the slope between the natural levee crest and major streams/rivers. It is a pioneer community, which is first to appear on newly formed sand bars and river margins. The area receives sands and silts with each flood. The soils are semi-permanently inundated or saturated. Soil inundation or saturation by surface water or groundwater occurs periodically for a major portion of the growing season. Such conditions typically prevail during spring and summer months with a frequency ranging from 51 to 100 years per 100 years. The total duration of time for the seasonal event(s) normally exceeds 25 percent of the growing season.” [LNHP. 1986-2004.]

Batture lands are essentially specialized riparian zones, specific to leveed floodplains. Riparian zones are defined as “transitional semiterrestrial areas regularly influenced by fresh water, normally extending from the edges of water bodies to the edges of upland communities.” [Naiman et al, 1] These riparian zones are normally characterized by successional vegetation, since they are new landforms. Ecological succession is the observed process of change in the species structure of a community over time. Since the batture land is often in state of flux due to flooding, climax communities along batture lands is rare.  [Klimas]

Vegetation and the River Bank Erosion Process

Vegetation has a direct effect on the erosion of banks. There are several ways in which vegetation can affect the erosion process: through the growth of fibrous roots systems, canopy interception and transpiration, large woody debris, woody vegetation cover and sediment yield. [Bennett]

Soil is generally strong in compression, but weak in tension, whereas fibrous tree roots are strong in tension but weak in compression. Therefore, root-permeated soil makes up a composite material that has enhanced strength. Root diameter has a direct effect on the strength of the soil, with smaller, more fibrous roots contributing greater strength. [Bennett]

Vegetation increases bank stability by intercepting rainfall that would otherwise have infiltrated into the bank and by extracting moisture for transpiration. Transpiration is the loss of water from plants by evaporation. Both processes enhance strength by reducing positive pore-water pressure and encouraging matric-suction (capillary suction exerted by the soil matrix that induces water to flow into unsaturated soil). [Bennett]

The introduction of large woody debris (LWD) in rivers is a result of natural tree death, beavers or other wildlife, debris flows or stream bank failure, or timber harvesting.  LWD can have a marked effect on channel hydraulics by diverting channel flow, causing local scour, channel widening, and also creating sites of sediment storage.  When LWD accumulates it can provide a number of benefits to the surrounding biotic communities, such as the creation of fish refuges, deep pools that increase habitat diversity, stable surfaces for organism growth and development, and canopy cover for reduced water temperature. [Bennett]

Because riparian vegetation exerts profound influences on hydrologic and fluvial geomorphic processes, it strongly affects sediment yields, sediment contributions from channels and styles of morphologic adjustment. [Bennett]

Specifics of Plant Communities Occupying the Batture

For the purposes of identifying plant communities, trees are the most reliable way to record the activity with in a community, because of their longevity.  Several pioneer species dominate the batture lands, and indicate rapid successional growth along the batture. As mentioned, it is relatively uncommon to find a climax community growing along a batture.

Salix Nigra (black willow) is a temporary, short-lived pioneer species of very rapid growth. Populus deltoides (cottonwood) will outgrow willow and become dominant except where frequent and extended growing-season flooding covers the trees and limits its growth. As sediments build up in the community and succession progresses, willow and cottonwood become less dominant and secondary associates gain increasing importance in the community. Communities often succeed into Hackberry-American Elm-Green Ash or Sycamore-Sweetgum-American Elm Bottomland Forest. [LNHP. 1986-2004]

Black willow is the most commonly found tree species on the battures, and cottonwood is the primary associate. Secondary species may be, depending chiefly on successional stage, Betula nigra (riverbirch), Fraxinus pennsylvanica (green ash), Platanus occidentalis (American sycamore), Carya illinoensis (pecan), Celtis laevigata (hackberry), Acer rubrum (red maple), Forestiera acuminata (swamp privet), Planera aquatica (water elm), Ulmus americana (American elm), Taxodium distichum (baldcypress), Acer negundo (box elder) and Morus rubra (red mulberry). Salix interior (sandbar willow) may be common in certain sites. [LNHP. 1986-2004] Sapium sebiferum (Chinese tallow) is also a common nonnative/invasive species found on the battures.

DeSoto Park observed tree species included mostly Black Willow, Cottonwood and American Sycamore and Chinese tallow. Acer negundo (Boxelder), Cornus Drummondii (Rough leaf dogwood), and Red Mulberry were also observed on the site. The site also includes many species of vines and ground cover.

Which types of batture lands will develop into which communities is heavily dependent on the age of the land and the distance from the channel. Older lands farther from a channel generally have more potential for future wildlife habitat values. A study conducted by the US Army Corps of Engineers determined that Cottonwood-Willow stands on older lands away from the channel have the potential to be intensively managed to a Sweetgum-Oak composition within decades, while 150 years or more may be required for a Cottonwood-Willow stand on newly accreted land to succeed to Sweetgum-Oak. [Klimas]

Another study conducted by the US Army Corps of Engineers explored which plant communities could grow along Mississippi River revetments. Revetments differ from battures in that they are purely man-made constructions. The common materials are concrete mats, asphalt paving, and loose rock paving (rip rap). Of these materials, the rip rap supported the most plant growth, with plant growth only occurring in cracks and seems along the pavement of the other two materials. In general, only two species of trees occurred on the lower half of the revetments, Salix nigra and Salix interior, however the upper banks supported a more diverse tree species assemblage. Vines and ground cover were the major component of plant communities on the revetments, but some species of annual plants managed to colonize the lower revetments where sediment was deposited after the river receded. [Webb et al.]

Human Influence on Batture and Riparian Systems

Riparian ecologies are adapted to exploit the dynamic nature of river systems. The cottonwood tree is an impressive example of this adaptation. Cottonwood seeds deposited along the river germinate only during a brief period of suitable moisture content on fine sediment as floodwaters recede. To release the seed has to coincide precisely with the flood recession so as not to wash away or dry the substratum so quickly that seedling roots cannot grow fast enough to stay in contact with the capillary fringe of the water table. [Naiman, et al]

It is this type of spatial relationship developed by living beings between themselves and their environments that shapes the processes that drive the dynamics of populations, communities and ecosystems. To understand the spatial organization of an environment is to see the whole of an ecosystem without knowing the minutia of details that make up the sum of its parts.

In this same respect, human modification of a natural system that they themselves caused to exist can be a confusing ethical issue. Is it better to allow these riparian systems that have developed along the battures and the man-made levees to follow their own successional, “natural” path or modify them to produce some perceived wildlife benefit? Individuals will invent a justification on either side based on personal experience, social culture, and where they are from. A useful philosophy to consider then, is in this quotation: “’Nature’ cannot be divorced from ‘man and society,’ requiring one to be open to other disciplines often better qualified to study spatial organizations and humans (such as geography, history, anthropology, economy, and sociology). This also requires one to incorporate symbolic and aesthetic values and to remember that every landscape has witnessed a culture and therefore has a memory as well as an environmental savoir faire created and recreated with time.” [Naiman, et al, 11]

Bibliography and Works Cited

Bennett, Sean J., and Andrew Simon. Riparian Vegetation and Fluvial Geomorphology. Washington, D.C.: American Geophysical Union, 2004. Print.

“Bouvier’s Law Dictionary, 1856 Edition.” Index. Web. 11 Mar. 2011. <http://www.constitution.org/bouv/bouvier_s.htm&gt;.

Chapman, S.S., Kleiss, B.A., Omernik, J.M., Foti, T.L., and Murray, E.O., 2004, Ecoregions of the Mississippi Alluvial Plain (color poster with map, descriptive text, summary tables, and photographs): Reston, Virginia, U.S. Geological Survey (map scale 1:1,150,000).

LNHP. 1986-2004. The natural communities of Louisiana. Louisiana Natural Heritage Program, Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA.

Naiman, Robert J., Gene E. Likens, Michael E. McClain, and H. De%u0301camps. Riparia: Ecology, Conservation and Management of Streamside Communities. Burlington, MA: Elsevier Academic, 2005. Print.

United States. US Army Corps of Engineers. Mississippi River Commission. Forest Vegetation of the Leveed Floodplain of the Lower Mississippi River. By Charles V. Klimas. Vicksburg, 1988. Print.

United States. US Army Corps of Engineers. Mississippi River Commission. Vegetation Development on Revetments Along the Lower Mississippi River. By James W. Webb and Charles V. Klimas. Vicksburg, 1988. Print.

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