Infiltration rates and soil moisture in a groved mulga community near Alice Springs, arid central Australia: evidence for complex internal rainwater redistribution in a runoff–runon landscape

Abstract

Spatial patterns of soil moisture and infiltration rate in a groved mulga woodland in arid central Australia are described. Infiltration rates within groves were measured with miniature cylinder infiltrometers set out in transects radiating from mulga stems, and extending into open sites beyond the plant canopy. Infiltration rates are highest close to stems, and decline rapidly with increasing distance, following a power-function relationship. This pattern of radially declining infiltration means that the soil surface within groves exhibits widely varying infiltration rates that are in some locations indistinguishable from those of intergrove soils. Contour-normal transects of surface soil moisture content and unconfined compressive strength were run across multiple wavelengths of the repeating mulga grove pattern. Soils within the lower intergroves were indistinguishable from those in the upper parts of groves in terms of these properties. Consequently, the position of the intergrove—grove boundary between these two locations could not readily be accounted for by the observed soil properties. Other factors (such as nutrient availability) may be involved in fixing the position of intergrove–grove boundaries, and this suggests the need for additional investigation of the mechanisms controlling the form of these patterned woodlands.