Soil-landscape evolution on a Mediterranean high mountain

During the Quaternary, Sierra Nevada (southern Spain) was affected by sever al glacial-periglacial episodes, decreasing progressively in intensity with time. These cold episodes alternated with the ones characterized by landsc ape stability and soil formation. Twelve soils that were formed on pre-glac ial surfaces and glacial deposits of various ages were studied in four sect ors: Laguna Seca, Lanjaron Valley, Mulhacen Valley, and Corral del Veleta. The soil parent material in all of these sectors was mica schist. Organic m atter content, cation exchange capacity (CEC), exchangeable bases, saturati on degree, and pH, were found to be not correlated with the age of the surf ace. The macromorphological differentiation of the soils, their clay and Fe -d contents, and especially, the clay and iron oxide accumulation indices, increased with the relative age of the surface. In contrast, the Fe-o conte nt and the Fe-o:Fe-d ratio diminished with the age of the surface. During t he last few pedogenic episodes, soils were formed by strong leaching and ac idification, but with very little chemical weathering. All of these feature s suggest that climatic shifts during the pedogenic episodes towards condit ions less favourable to soil development, in addition to vegetation changes and disturbances on the soil surfaces, which started by periglacial proces ses, account for the soil evolution of the Sierra Nevada better than time a s the only variable factor. The soils did not develop monotonically with ti me and the sequence of surfaces cannot be regarded in a strict sense as a c hronosequence. The soils developed over a series of stepped pedogenic episo des; in each episode, especially in the oldest, the properties of the soils related to weathering could have approached or reached a steady state. Nev ertheless, when these properties are plotted against time, a continued incr ease in soil development results. (C) 2000 Published by Elsevier Science B. V. All rights reserved.