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Abstract: In arid and semiarid rangelands, soil erosion has been widely considered an important soil degradation process and one of the main factors responsible for declining soil fertility. In this study, we determined the sediment production and the enrichment ratios of clay, organic C, and total N by using rainfall simulations on runoff plots (0.60 × 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that spatial variability in soil loss rate and enrichment process exists as a result of the local differences in both plant composition and soil surface characteristics. Sediment production was significantly lower in the GS (14.2 g m−2) compared with the DGS and DSS (38.2 and 51.5 g m−2, respectively). In the GS, the enrichment ratio of clay was significantly greater (3.9) and enrichment ratio of organic C was lower (3.1) than in the DGS and the DSS, though differences in enrichment ratios of total N were not significant. The high rate of soil loss and nutrients through overland-flow may limit the opportunities that promote the pathway from DGS back to GS community, favoring the dominance of shrubs. [Copyright &y& Elsevier]

Abstract: In grazed semiarid ecosystems, considerable spatial variability in soil infiltration exists as a result of vegetation and soil patchiness. Despite widespread recognition that important interactions and feedbacks occur between vegetation, runoff and erosion, currently there is only limited quantitative information on the control mechanisms that lead to differences in infiltration from different vegetation types. In this paper, we determine (i) the relationship between vegetation and soil surface characteristics and (ii) the soil infiltration rate by using rainfall simulations on runoff plots (0.60 × 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that vegetation and soil infiltration are closely coupled. Total infiltration was significantly higher in the GS (69.6 mm) compared with the DGS and DSS (42.9 and 28.5 mm, respectively). In the GS, soil infiltration rate declined more slowly than the others communities, reaching a terminal infiltration rate significantly greater (57.7 mm) than those of DGS and DSS (25.7 and 12.9 mm, respectively). The high rate of water losses via overland-flow may limit the possibilities for grass seedling emergence and establishment and favor the persistent dominance of shrubs. [Copyright &y& Elsevier]

Abstract: The Valdes Peninsula has the most noticeable aeolian landforms of the Patagonian drylands. The southern sector of the peninsula is affected by the advance of several fronts of active sand dunes grouped in discrete megapatches. The objectives of the study were to: (1) analyse the morphology of sand dunes, and (2) measure the migration rates and orientation of the sand dunes along a 33-year period (1969–2002). These studies used a series of field techniques in conjunction with aerial photography and satellite data, such as AVIRIS and Landsat imagery. Four main types of active sand dune forms were identified: (1) compound linear; (2) compound transverse; (3) compound dome-shaped; and (4) complex dome-shaped. Because of the windy climate, dune mobility is high; there is an eastward migration to an average speed of 9.1±2.7myr−1. Despite this high rate and since observed changes in the total area of active dunes were small, active processes of vegetation encroachment are deducible. Thus, wind and effective rainfall appear as the main factors regulating the process, in short and long-term, respectively. Although the orientation and disposition of the dunefields is in agreement with the prevailing west winds, the active dunes present a variety of forms, which reflect local variations in the wind flow. The circulation is strongly influenced by the shape of the coastline and the actual existence of the dunefields is due to this friable windward coast found nowhere else in Patagonia. [Copyright &y& Elsevier]