GEOLOGIC CONTROLS ON SECONDARY SUCCESSION IN AN ABANDONED CORN FIELD

The geologic processes of bedrock weathering and soil genesis, and the resulting hydrologic pathways have contributed to the spatial distribution of plant species in an abandoned Southern Indiana corn field during c. 35 years of secondary succession.

In this old field, fractures in the thin (c. 10 m), underlying limestone bedrock, sinkhole features, human activity, bioturbation, and topographic effects (low relief valleys and ridges) have contributed to the spatial variability in the hydrologic and chemical characteristics of the soil. The upper parts of most of the soils have been homogenized by agriculture so that well defined A/B horizon delineation is not common, and soil nitrogen values from a grid of study plots indicate a uniform nitrogen distribution across the field, with the exception of one plot with a high vegetation density.

Tree species and size data indicate that pine-dominated study plots tend to have low biodiversity, with the exception of a pine-dominated plot located in a topographically low area having a much greater Shannon biodiversity index value than the plots on topographic highs. Plots dominated by grasses or deciduous trees tend to exhibit greater hydrologic variability and higher biodiversity values than the pine-dominated plots.

Multiple scales of hydrologic variability have influenced the plant species distribution in this old field. Topographically low regions with moist soils and areas with sub-meter hydrologic variability have greater biodiversity than hydrologically homogenous upland areas.