Land use change effects on abandoned terraced soils in a Mediterranean catchment, NE Spain

Abstract

The Serra de Rodes catchment (NE Spain), enclosed in the Natural Park of Cap de Creus, represents a typical Mediterranean ecosystem. This semiarid environment, with hot summers and mild winters, has been progressively abandoned by farmers during the last century. Nowadays, most of hillside soils are abandoned and only small patches of vineyards and olive trees are cultivated with very low management and incomes. In this study, we have assessed the effects of land use and land use change on the main soil quality parameters. Along two altitudinal gradients, we selected 11 random environments representative of the current land uses, in sequence from cultivated to early abandonment. The different vegetation stages were grouped in four main land use types according to the age of abandonment: cultivated fields (vineyard and olive trees, 0 years), recent abandonment (dense and cleared shrubs, 5 years), mid-abandonment (cleared cork trees and dense olive trees, 25 years) and early abandonment (dense cork trees and pine trees reforestation, 50 years). Erosion plots were installed in the previously selected environments for soil physicochemical characterisation, throughout 1-year observation, monitoring nutrient losses, runoff volume and sediment yield data. Analysis of variance (ANOVA) indicates significant differences in the main soil quality parameters such as soil organic matter (SOM), total nitrogen (N), water holding capacity (WHC) and pH, among the selected environments under different land use conditions. Factor analysis of the principal components (PCA) enabled the identification of three soil quality indices: index of soil erosion and nutrient losses (SENL), index of soil quality and fertility (SQF) and index of vegetation cover and soil protection (VCP). Soil organic matter, nutrient supply, soil vegetation cover and soil compaction are critical for soil degradation in these environments and they must be managed appropriately in order to ensure continuous soil rehabilitation. Furthermore, the main conclusion that may be drawn from this study is the significant influence of land use on the main soil quality parameters.