Ecohydrologic Effects of Soil Mosaics in Patterned Australian Drylands

Ecosystem patterning is widespread in the Australian drylands. The spatial ecosystem mosaics may have morphologies ranging from vegetation patches of irregular shape and size, to near-perfect contour alignment of elongate vegetation bands. Differences in canopy rainfall interception and stemflow funnelling contribute to distinctly different water balances of groves and intergroves. These may be further amplified by difference in loadings of organic litter, which may also intercept significant amounts of the scant rainfall. However, the primary source of hydrologic distinctiveness of groves and intergroves is differentiation in soil properties. Among soil properties that have ecohydrologic importance are surface properties, including the presence and extent of development of inorganic and biological soil crusts; soil organic matter content and related changes in soil structure; soil infiltrability, which is in part related to faunal macroporosity, and surface stone mantles. Additionally, at the local scale, textural differentiation of the mineral soil component becomes significant, especially where shrub mounds of aeolian and splash-transported fine sands have developed.

Patterned Australian dryland ecosystems can exhibit wide variation in these key soil properties over quite small spatial scales. Variation may be apparent over one or two canopy radii around individual shrubs, but may additional be developed systematically within groves and intergroves as a result of sediment translocation in surface runoff. In these ecosystems, it becomes apparent that conventional soil taxonomy and soil mapping are unsuitable tools for the analysis and reporting of relevant soil ecohydrological properties.

This presentation will illustrate these points using results from a range of Australian dryland ecosystems, including mulga (tall shrub), chenopod, and tussock grassland environments. Aspects of the ecohydrology of these ecosystems that remain in need of investigation will be highlighted.