Wind Erosion in Western Queensland Australia

Chapter 2 – Land Erodibility ControlsA number of microbiotic (biological) crust types exist. These are characterized by thebiological organisms driving crust formation. Organisms associated with microbiotic crustformation include: mosses and liverworts, lichens, fungi, algae, cyanobacteria, and othermicrobiota. Microbiotic organisms facilitate crust formation by binding soil particles togetherthrough secretion of gels or binding with structural filaments. Crust classification systemshave been proposed based on surface micro-topography of the crusted soil (Eldridge andGreene, 1994; Johansen, 1993). These include: smooth, rugose, rolling, and pinnacletopographies. These surface structures generally reflect the climate of the region ofoccurrence. For example, smooth crusts are associated with hot hyper-arid habitats, whilstpinnacled crusts are associated with cold climates in which frost heaving occurs (Belnap etal., 2001a). As for physical crusts, climate, soil texture, and soil chemistry play importantroles in biological crust formation and structural characteristics. The presence and type ofvegetative cover also affect biological crust formation. Vegetation affects the ability ofprecipitation to reach the soil (or crust) surface, and in a species-species competition sense(Belnap et al., 2001b).Physical and microbiotic crust formation are particularly sensitive to climate and soil texturalcharacteristics. The amount, intensity, and frequency of precipitation determine the type ofphysical crust formation, and where present, biological crust growth or degradation (Belnapand Gillette, 1998). In addition to these factors, the precipitation efficiency is regulated bysolar radiation intensity and potential evaporation. These latter factors influence the rate ofsoil particle transport, deposition and binding, and the ability of microbiotic organisms toutilise the moisture, or in fact survive close to the soil surface. Soil texture, in particular sandand clay content, have been found to affect the soil particle binding, and habitat suitability formicrobiota (Diouf et al., 1990; Skidmore and Layton, 1992). Physical crusts do not formreadily in sandy soils due to a lack of fine particles required for inter-particle binding. Loamyand clay textured soils, however, provide conditions suitable for inter-particle binding byphysical (structural and depositional) processes, and stable habitats for crust formingmicrobiota.While crust formation may be triggered by precipitation, crust degradation or breakdownoccurs as a result of photo-degradation, burning, structural breakdown (e.g. in self-mulchingsoils), trampling by livestock, mechanical disturbance, and in the case of biological crusts,death (Eldridge and Green, 1994; Belnap and Eldridge, 2001). The extent and intensity of51