Feedbacks between fires and soil erosion processes in desert grasslands: Implications for land degradation

Dr. Sujith Ravi, of UA B2 Earthscience, presents the Brown Bag Seminar on "Feedbacks between fires and soil erosion processes in desert grasslands: Implications for land degradation".

Abstract: Hydrological and aeolian processes are major drivers in the dynamics of arid landscapes in that they redistribute soil resources with important implications on the composition and spatial patterns of dryland vegetation. These processes are thought to play a major role in the conversion of disturbed desert grasslands into shrublands, with possible impacts on regional climate and desertification. At its early stages the grassland-to-shrubland transition is thought to be reversible and fires have been shown to contribute to the reversibility of the system. Even though fires are known to interact both with wind and water erosion, an understanding of these interactions and of their effect on aridland degradation is still missing.  Here using replicated field manipulation experiments and wind tunnel studies it is shown that fires tend to counteract the heterogeneity-forming dynamics of land degradation associated with shrub encroachment, by enhanced post-fire redistribution of soil resources from the fertile shrub-dominated areas (or “fertility islands”) to the bare soil interspaces. The enhancement of post-fire redistribution of soil resources is attributed to the enhancement of post fire soil erodibility, in particular, erosion by wind, which dominates in these landscapes. Further, the possible impacts of fire-erosion interactions on vegetation composition and structure are investigated using a spatially explicit model of vegetation dynamics. The modeling study shows the possible long-term effect of fires on the stability and resilience of fertility island systems. In particular, it is found that the fertility islands are dynamic rather than static features of these landscapes.