The effect of land parameters on vegetation performance and degree of erosion under Mediterranean conditions

Important land parameters such as soil texture, soil depth, topography, parent material, and climatic conditions were studied in a semi-detailed soil survey conducted in the island of Lesvos, and were related to the vegetation performance and degree of erosion. Rainfall data indicated that the island could be divided into two major climatic zones: a semi-acid (western part) and a dry sub-humid (eastern part). A 45% rainfall gradient has been recorded in the above two climatic zones. The great reduction in rainfall combined with the higher evapotranspiraton demands in the semi-arid zone has significantly affected vegetation performance and degree of erosion in the area. Due to the general lack of available water, the semi-arid part of the island is dominated by poor marquis vegetation, while olive trees, oak and pine forests prevail in the dry sub-humid part under similar topogaphical and geomorphological conditions. Vegetation cover increases with increasing rainfall and soil depth. Slope grade has a variable effect on soil erosion in the various climatic zones. Erosion is decreasing with increasing rainfall for the same slope classes. Severely eroded soils prevail in the semi-arid zone with slopes greater than 12%, while slightly to moderately eroded soils are found in the dry sub-humid zone under similar slope classes. The highest rates of land degradation have been measured in areas with soils formed on pyroclastic formations. Areas with soils formed on basic igneous rocks, shale and lava are well vegetated and protected from erosion under a broad range of slopes and weather conditions. (C) 2000 Published by Elsevier Science B.V. All rights reserved.