Abstract
A large part of the agricultural terraces in mountain environments are abandoned, like those from the Filabres range in Almeria, SE Spain. While many of such terraces show signs of soil erosion (wall disruptions, surface crusts, pipes and gullies), others in steep slopes remain well preserved after 50 years since their abandonment and still seem to play an active role against soil erosion. In order to know both magnitude of soil erosion and controlling factors in different types of abandoned terraces, a rainfall simulation campaign with a portable sprinkler was carried out in 45 representative microsites. Runoff, derived-infiltration and sediment production were measured and their relationships to basic soil parameters (particle size distribution, pH, EC, organic matter content, aggregate stability), geomorphic position, and ground cover, were examined. Under the average applied rainfall intensity (48 mm/h, which represents a precipitation with a return period of 5 years in the area), narrow bench terraces from steep hillslopes, have larger infiltration values and deliver less sediments than large bank terraces in alluvial plains. The presence of stony pavement sieving crusts on narrow-bench terraces and also on un-terraced alluvial fans, play an essential armouring effect against soil erosion while favouring water infiltration. Considerations are made about the evolution of the different types of traditional terraces in the area under both past agricultural and present abandoned status, and also about possible uses under a sustainable land management policy.
Highlights
In many parts of semiarid mountains of SE Spain, the landscape is partly covered by many types of agricultural terraces
Forty five rainfall simulations at an average intensity of 48 mm/h (5 years return period) in five landforms essentially associated to abandoned agricultural terraces have revealed that runoff coefficients and total infiltration are related to some landform attributes, like plant cover and slope gradient
SOLE-BENET et al (2002) reported that during the cultivation of Rambla Honda soils or just after their agricultural abandonment, sediment yields could have been much higher under rain intensities similar to those tested in this research due to the fact that large amounts of fines were available at the soil surface because of the tillage, even done by animal traction, but since the abandonment and once the rock pavement sieving crust (VALENTIN & BRESSON, 1992) is formed, its armouring effect decreases substantially sediment yields under later rainfall events (SOLE-BENET et al, 2002)
Summary
In many parts of semiarid mountains of SE Spain, the landscape is partly covered by many types of agricultural terraces. The southern versant of the Filabres range, in Almeria province, is one of such areas. Those terraces associated to ephemeral rivers are known to be many centuries old (GARCIA LATORRE & GARCIA LATORRE, 2007) and were irrigated, and sometimes still are, by diversion channels (boqueras) from the main one or from adjacent sloping contributing areas, known as jessour in the Maghreb (BALLAIS, 1990; SCHIETTECATTE et al, 2005). The terraces show a quite dense cover of the sparse bush Retama sphaerocarpa
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