Swamp

Natural Levee)

SLACKWATER AREAS fine textured soils

FRONT LAND medium textured soifs

Figure 4.15 Idealized section of a Mississippi alluvial plain. The vertical scale is exaggerated in showing the relationship between topographic position, soil, and tree cover.

these situations involve batture lands, those tracts between either natural or man-made levees and water courses, where water tables in summer may be too deep in the ground to enable capillary delivery of moisture through the sand. Other difficult sites for natural regeneration are those where plastic clay covers the surface of the soil. One finds such in low-lying flats underlain by hardpans and in silty-clay basins below terraces that border rivers. Under all of these conditions, either soil moisture or aeration periodically may be too limited to sustain stands of many species. Poor aeration under these conditions takes place where soil moisture is overly abundant.

Edaphic and Physiographic Characteristics

Many soils of the South's bottomlands exhibit azonal features. Such soils are too immature to display well-defined horizons within or between the surface- and subsoils. First bottoms, the major sites of relatively recent origin, compose the present main flood plain. Waters often overflow them. Impervious waxy clays, silts, and fine sandy loams prevail in these lands immediately adjacent to rivers. Second bottoms, lands which at an earlier time were the first bottoms of the same rivers, appear now as terraces slightly above a river's elevation. Second bottoms flood only occasionally. On them, acidic silt loam and silty clay loam are major textural classes

Other edaphic and physiographic zones of river bottoms include sloughs, swamps, ridges, flats, and fronts. Sloughs, sluggish side channels or rivulets from a river, may also appear as mudholes or marshy backwaters.29 Swamps are other secondary sites in both first and second bottoms. Swamps, except during extreme droughts, are inundated for the greater part of every growing season. Alluvial swamps along flowing rivers differ from tidewater and peat swamps of the Coastal Plain estuaries: the former have fairly firm clay bottoms which occasionally dry out, while water stands permanently in swamps composed of organic soils.

Ridges, the banks of former stream courses, stand 2 to 15 feet above surrounding flats. Although rarely flooded, seasonal overflows do deposit coarser soil materials on them, thereby providing better surface drainage than for most other topographic classes of bottomlands. Flats, lying between the ridges, have poor surface drainage because of the high proportion of clay in them. The perennial deposits of alluvium also discourage favorable internal (subsurface) drainage. In low flats, free water may take several weeks to subside after streams return to their banks; in high flats, a few days. Ridges and flats in the second bottoms become obscure as sheet erosion lessens their evidence. Battures, land between a river's bank and a levee, unless protected by engineered dikes, frequently flood.

Figure 4.16 Mixed hardwood stand in a southern river second-bottom. More than 25 valuable species for various uses grow in these sites where soil moisture is always adequate, but the land never flooded for more than a few days at a time. (USDA Forest Service photo)

In all bottomland sites, nutrient drain likely exceeds nutrient gain where forests are managed on short rotations. The element-demanding broadleaf trees, in contrast to coniferous species, utilize nutrients more rapidly than soil genesis permits their restoration. This is largely because leaching to streams of elements temporarily stored in living foliage begins shortly after leaf fall in the autumn of the year. Lightning strikes that release nitrogen from the atmosphere and accompanying rainfall that washes it to the ground cannot maintain the level of this essential nutrient for maximizing growth of these trees on these sites. Erosion, and with it the transfer of nutrients, plays a major role in maintaining nutrient levels adequate for broadleaf trees in bottomland biomes.

Figure 4.17 Overcup oaks seeded-in on the banks of this small oxbow lake prior to the river changing its course and thus creating the lake. Great numbers of seedlings appeared under these parent trees following a bumper seed crop and a spring and summer without rain. The following winter, after a month of high water on the site, all the seedlings had died.

Figure 4.17 Overcup oaks seeded-in on the banks of this small oxbow lake prior to the river changing its course and thus creating the lake. Great numbers of seedlings appeared under these parent trees following a bumper seed crop and a spring and summer without rain. The following winter, after a month of high water on the site, all the seedlings had died.

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