Soil-landscape evolution on a Mediterranean high mountain

During the Quaternary, Sierra Nevada (southern Spain) was affected by several glacial–periglacial episodes, decreasing progressively in intensity with time. These cold episodes alternated with the ones characterized by landscape stability and soil formation. Twelve soils that were formed on pre-glacial surfaces and glacial deposits of various ages were studied in four sectors: Laguna Seca, Lanjarón Valley, Mulhacén Valley, and Corral del Veleta. The soil parent material in all of these sectors was mica schist. Organic matter content, cation exchange capacity (CEC), exchangeable bases, saturation degree, and pH, were found to be not correlated with the age of the surface. The macromorphological differentiation of the soils, their clay and Fed contents, and especially, the clay and iron oxide accumulation indices, increased with the relative age of the surface. In contrast, the Feo content and the Feo:Fed ratio diminished with the age of the surface. During the last few pedogenic episodes, soils were formed by strong leaching and acidification, but with very little chemical weathering. All of these features suggest that climatic shifts during the pedogenic episodes towards conditions less favourable to soil development, in addition to vegetation changes and disturbances on the soil surfaces, which started by periglacial processes, account for the soil evolution of the Sierra Nevada better than time as the only variable factor. The soils did not develop monotonically with time and the sequence of surfaces cannot be regarded in a strict sense as a chronosequence. The soils developed over a series of stepped pedogenic episodes; in each episode, especially in the oldest, the properties of the soils related to weathering could have approached or reached a steady state. Nevertheless, when these properties are plotted against time, a continued increase in soil development results.