Wind Erosion in Western Queensland Australia

Chapter 4 –Modelling Soil Erodibility DynamicsA limitation to using data from studies of soil aggregation dynamics is that the temporalresolutions of these studies have varied from monthly to seasonal sampling, with datareporting at up to annual time scales (Table 4.1a). This coarse temporal resolution ofsampling has provided snapshots in time of soil surface conditions. These temporallydisparate samples have been pieced together to form soil erodibility time-series like thatpresented by Merrill et al. (1999), and have demonstrated dynamic responses of soils to interseasonaland inter-annual climate variability. Importantly, however, the resolution of thestudies is insufficient to identify immediate responses of soil surface conditions to rainfallevents or disturbance that may display the logistic behaviour in the model presented here.Studies reporting on soil crusting effects on wind erosion have been conducted in bothcultivated and rangeland environments (Table 4.1b). Unlike the studies monitoring dynamicsoil aggregation effects on wind erosion, the studies of soil crusting effects have been short induration. They have been experimentally based rather than monitoring soil crust-erodibilitychanges in response to climate variability and management. The focus of much of this workhas been on understanding disturbance effects on biological soil crusts and resulting changesin soil erodibility. Soil crust disturbance levels in these studies have been reported usingqualitative descriptors, e.g. ‘low’, ‘moderate’, ‘high’, as opposed to quantitative measuressuch as crust cover or crust strength (Belnap and Eldridge, 2001). These physical indicatorsof crust condition have not been consistently reported or acquired with standard measurementprocedures (Table 4.1b).Methods used to manipulate soil crust conditions have not been standardised. This has meantthat a range of disturbance mechanisms have been used, including trampling in heavy bootsto passing over the soil surface in a motorised vehicle (e.g. Gillette et al., 1982). Whilestudies examining disturbance impacts on soil crust conditions (Table 4.1c) have usedquantitative measures of disturbance intensity, these measures are proxies (e.g. animal dungdensity) for real disturbance intensities (e.g. stocking rates) that are required as input tospatially explicit models.The characteristics of these studies have important implications for applying the research inparameterising models of soil crust effects on wind erosion. The coarse temporal resolutionof monitoring studies (Table 4.1a), the lack of quantitative methods for defining soildisturbance intensities (Table 4.1b), and the poor transferability of disturbance methods and124