Hydric erosion in Sierra Magina olive groves (Andalusia, Spain) - Prospects for sustainable development

Olive growing has become a veritable monoculture in the Jaen Province, Andalucia, particularly since Spain joined the European Community. Hydric erosion has been studied in olive groves, in the Sierra Marina rural district, using Cs-137, an artificial isotope of caesium. The Villamorena reference site that has been stable for half a century gives a good marker for the other diagnostic samples. Overall, the main process is netlowering of the land surface: it reaches its maximum (at least 25 cm) at the local level with bared olive trees. It is high (at least 10 cm) at the level of small watersheds and still reaches about 5 cm at the level of land plots, even in accumulation forms such as fans. Accumulation, at least 15 cm, is only observed in the downhill fans of terraced watersheds and in the pozas (small pits) dug at the foot of olive trees. The combination of Mediterranean climate, relief and lithology constitutes very favourable conditions for hydric erosion. Especially in autumn, intense rains rapidly saturate the soil surface and allow the appearance of early overland flow. Our results confirm studies that have demonstrated the role of soil tillage in olive grove soil erosion. This work brings new elements about the moderating effect of traditional ways of fitting out slopes and the persistence of natural elements in the landscape which was disregarded by previous studies. These results draw new perspectives for soil conservation and sustainable development in rural Mediterranean mountains.