Fire and aspect induced differences on the erodibility and hydrology of soils at La Costera, Valencia, southeast Spain

Abstract

This paper presents measurements of soil aggregation parameters and rainfall simulation experiments from areas of Mediterranean scrubland vegetation in La Costera district, in the southern part of Valencia Province, Spain. Data were obtained using a portable rainfall simulator and from laboratory studies of aggregate stability, using the water-drop test and ultrasonic dispersion methods. Three locations were chosen to enable the influences of aspect and the post-fire recovery time of the vegetation on soil erosion and hydrology to be investigated. The slopes studied were (a) a north-facing slope burnt ten years before the experiment, (b) a south-facing slope burnt at the same time, and (c) a north facing slope, burnt two years before the experiment, similar to slope “a” in terms of its basic characteristics. The experiments demonstrate the importance of both wildfires and aspect on hydrological and erosional soil surface processes. The north facing slope at La Costera (slope a) has a higher aggregate stability than the corresponding south facing slope (slope b). The recently burnt north facing slope (c) is intermediate in terms of aggregation, but has the most erodible soils because of the lower infiltration rates and the low vegetation and litter cover. Nevertheless, for the slopes burnt ten years previously, the south-facing slope is more erodible than the north-facing one. The results suggest that the forest fire ten years ago did not produce a persistent degradation of the ecosystem, only higher soil and water losses during the first years following the fire. A southern aspect, where vegetation recovery rates are slower and the hydraulic stress is higher, favours the development of soils with a relatively low aggregate stability.