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An Ecological Interpretation for the Small Mounds in Landscapes of Eastern Oklahoma¹

ABSTRACT

Many hypotheses suggesting the origin of small, oval, slightly domed mounds have been proclaimed but none widely accepted. Mounds typical to eastern Oklahoma were studied by relating climatic influences, patterns, distributions, sizes, shapes, relief, vegetation, and biological evidences to morphological characteristics of soil pedons within the mounds and associated landscape. Laboratory measurements included particle-size distribution, bulk density, extractable cations, and organic matter extractions.

Mounded soils occur in the greater than 102-cm rainfall belt on landscapes having occasional perched water tables. The pattern of the mounds which consists of sizes, shapes, and distribution is similar in these landscapes.

The average yield per hectare of forage was 4,997 kg on the mounds as compared to 3,227 kg in the intermound areas.

Evidence of biological activities is highly concentrated in mounds, increasing in the soil horizons where mottlings decrease due to decreasing wetness. Even though soil textures are similar, bulk densities show soils to be more porous in the mound than in the associated intermounds. The surface horizons of the mound soils are apparently continually "fluffed" by organisms and protected by a flourishing growth of vegetation sustained by the high productivity of these soils.

Mounds are concluded to be natural phenomena resulting from a soil environmental equilibrium, a condition created by the influence of a complex ecological association of a protective cover of grasses, and organisms of the landscape assembling in selected elevated soils to escape seasonal wet soil conditions.

Key Words: ecological relationship • mima mounds • biological origin

¹ Contribution from the Oklahoma Agr. Exp. Sta., Stillwater. Journal Manuscript No. 2640.

² Graduate Student and Professor of Soil Science, respectively, Department of Agronomy, Oklahoma State Univ., Stillwater 74074. The senior author is Soil Scientist, Soil Conservation Service, USDA Eufaula, Okla.

Received for publication April 6, 1973.