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Mel Neave and others Division of Geography, School of Geosciences, Madsen Building (F09), University of Sydney NSW, 2006 Australia Abstract: Semiarid environments typically exhibit low and unevenly distributed vegetation covers. This creates, at the coarsest level, a binary system of vegetated and unvegetated surfaces that behave quite differently in terms of their geomorphic responses. In the Jornada del Muerto Basin in southern New Mexico, USA, vegetation changes over the last 100 years have transformed the landscape from one covered by semidesert grasslands to a shrubland dominated system. These variations in the biological character of the environment have contributed to alter geomorphic functioning. Thus, biological and physical processes are intimately linked within this system. This paper aims to investigate the nature of biophysical interactions in the Jornada del Muerto Basin through an examination of current knowledge on erosion processes on a hillslope in the basin. This hillslope, known as Summerford bajada, has been the focus of numerous geomorphic and ecologic studies but links between the findings of such research are often not undertaken. Therefore, the goal of this paper is to produce a conceptual model that considers the multi-faceted nature of physical and biological links within this system. At a fundamental level, the erosion of Summerford bajada is dominated by fluvial processes. However, the volume of runoff generated and its ability to undertake change is greatly affected by the distribution of vegetation across the surface. This ultimately controls processes such as crust development and soil infiltrability, which influence runoff and sediment generation. Thus, biophysical interactions in semiarid environments, such as the Jornada del Muerto Basin, represent non-linear systems that exhibit multiple feedbacks. Biophysical interactions in semiarid regions, however, extend beyond relations between vegetation, runoff and erosion. Animal activities also contribute to alter rates of sediment movement from surfaces with low vegetation covers but have less of an impact on well vegetated environments. This response appears to be related to the formation of raindrop induced surface crusts on soils that are not protected by vegetation canopies. Digging by small mammals disrupts the crusts making loose sediment available for transportation by overland flows. Combined, these results indicate that biophysical interactions in semiarid environments such as the Jornada del Muerto Basin represent non-linear systems that exhibit multiple feedbacks. This creates complex response networks between the biological and geomorphic systems of semiarid environments and highlights the need for integrative investigations in these regions. |
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