Native Vegetation

Native Vegetation

The organic material in soil comes from the plants growing in the area and is modified by the animals, insects, and microorganisms living there. The effect of vegetation is strong enough to influence the chemical and physical properties of the soil as well as its biological characteristics. For example, a soil formed under forest vegetation is usually more acid and has had more clay movement from the A horizon to the B horizon than a soil formed under similar conditions but developed under grass vegetation. The resulting soil differences persist for hundreds of years even if the vegetation changes. Consequently, it is possible to identify the native vegetation of a soil that has long been under cultivation, or a prairie-derived soil now under trees.

For contest purposes, native vegetation will be classified as forest, transition, prairie, or marsh. These types can be identified as follows:

FOREST

The A horizon formed under forest is usually no more than 3-6 inches thick and is underlain by an E horizon. The Ap horizon produced by tilling a forested soil contains a mixture of A and E materials that usually are lighter colored than an Ap in a prairie soil. The B horizon has a marked accumulation of clay, and both A and B horizons tend to have an acidic pH unless lime has been applied to neutralize the surface soil.

TRANSITION

Soils that show the influence of both grass and trees have A horizons nearly as dark as those of prairie soils but have E horizons between the A and B horizons (unless the E horizon is destroyed by tillage and/or erosion). Typically, the A horizons are between 6 and 10 inches thick if uneroded. The E horizons are less distinct than those developed under full forest vegetation and are commonly 1-3 inches thick. The B horizon development also tends to be intermediate between forest and prairie soils.

PRAIRIE

Soils developed under grass vegetation usually have thick, dark, and moderately dark A horizons unless the soil is so steep that major erosion has occurred or the soil is located on a floodplain and has received recent deposits of light-colored sediment. Prairie derived soils can have E horizons but only if they have poor internal drainage resulting from flat or concave topography and clayey subsoils. The B horizons usually have less clay accumulation than soils formed under forest vegetation occupying adjacent landforms and developed in similar parent material.

MARSH

Reeds, sedges, cattails, and other water-loving vegetation grow in areas so wet that organic materials accumulate and form peat. The particular kind of vegetation can often be identified from the nature of the peat, and are generally associated with Histosols.

Human Impact

Due to increasing human impact on soils, including accelerated erosion, material transport, significant tillage, or other impacts, original depth of topsoil and landscape
should be provided to determine the native vegetation.