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Aim To investigate the role of clay in limiting the development of woody biomass in drylands. Location Australia. Methods Spatial data representing woody biomass, soil clay content and climate for the Australian continent were interpreted to explore the relationship between a moisture index and woody biomass on clay and non-clay substrates. Moisture and soil water potential were investigated through time for clay and sand plains. Sub-soil clay and other soil characteristics were compared between areas with and without high tree mortality after drought. Results The substantially lower woody biomass on clay soils than non-clay soils in the drylands of the Australian continent verifies the inverse texture effect. A clay floodplain consistently held more water than an adjacent sandplain, but soil moisture in the clay was effectively inaccessible to plants for much longer periods because of more negative values of water potential in the clay soil. Small increases in sub-soil clay were associated with high tree mortality. Main conclusions Our findings suggest that the 'inverse texture effect', which describes the negative association of woody biomass with soil clay content in drylands, may mostly relate to the moisture-retentive properties of clay rather than being caused by reduced infiltration and enhanced evaporation from clay-rich soils. Our evidence suggests that clay soils constrain woodiness in drylands by exacerbating water stress, and confirm the fundamental role of aridity in determining woody biomass and the global distribution of grassland. [ABSTRACT FROM AUTHOR]

A method is proposed to estimate the threshold wind speed for dust emissions as a function of soil moisture in arid regions. This method, which is applicable at the local scale, employs a model of the surface heat budget to estimate the spatial distribution of thermal inertia-derived soil moisture (TISM) and an analytical footprint model to estimate dust source areas. It incorporates readily available satellite and meteorological data. The soil moisture inside the dust source area is estimated for individual dust phenomena observed at a synoptic surface observation site, and then, together with the corresponding observed wind speed, the threshold wind speed as a function of soil moisture is found by employing the parametrization of Fécan et al. (Ann Geophys 17:149–157, 1999). This relationship represents the local dust climatology at the observation site, although the data include some outliers. The results show that readily available data for the natural environment can be used, as an alternative to wind-tunnel data, with the parametrization used to derive the threshold wind-speed relation. The derived relation indicates the TISM and wind speed at which the probability of a dust phenomenon is 10%. Moreover, the threshold wind-speed results are not sensitive to the principal footprint-model parameters. The TISM standard error of approximately 0.04 m3 m−3 could significantly affect the results under dry and weak-wind conditions, but this sensitivity can be avoided if the soil clay content or the soil type at the observation point is known. [ABSTRACT FROM AUTHOR]