Role of rapid vegetation changes and disturbances on dust emissions

Background/Question/Methods

Aeolian processes redistribute sediment and nutrients within desert landscapes with important implications for vegetation and land degradation. The differential rates of soil deposition and erosion by aeolian processes can result in differential rates of hydrological processes such as run-off and infiltration; with implications for vegetation patterns. Vegetation structure and patterns, in turn, affect the spatial dynamics of sediment transport, soil moisture, and nutrients in the system. Desert grasslands and shrublands are highly susceptible to accelerated soil erosion by wind following disturbances (e.g., fires and grazing). Moreover, these ecosystems worldwide are threatened by contemporary shifts in vegetation composition (e.g. encroachment by shrubs, invasion by exotic grasses), which alter the frequency and intensity of disturbances and dust emissions. Here, using extensive wind tunnel studies, field experiments (in grasslands and shrublands of North America) and modeling, the interactions among hydrologic-aeolian processes and vegetation dynamics are demonstrated. The goal was to identify the effects of the interactions of contemporary vegetation changes and disturbances on dust emissions.

Results/Conclusions

Results highlight the role of vegetation shifts and disturbances in altering the timing and magnitude of dust emissions.  In particular, grassland and shrub-encroached grasslands exhibit comparable aeolian activity soon after disturbance, but the duration of accelerated dust emissions (“window of disturbance”) is shorter in the case of grasslands. Thus, shrub encroachment coupled with disturbances such as fire as well as strong winds and persistent dry conditions may lead to irreversible loss of resources. On the other hand, fires in some shrub-encroached grasslands may have a beneficial effect, where prescribed fires can result in the progression towards a grassland state, due to post-fire enhancement of sediment redistribution and resource homogenization. The degree of post-fire aeolian transport and its attenuation with time was found to be strongly affected by the antecedent vegetation type and post-fire climatic conditions. The interactions among sediment transport processes, disturbances and vegetation dynamics are explored from patch to landscape scales and their roles in dust emissions and land degradation are discussed.