Tasas de erosión laminar históricas en dehesas

Résumé

In this work, a methodology is presented to estimate historical soil erosion rates using the inflection point (IP) of trees whose roots have been partially exposed, which is validated with the 137Cs technique. In addition, a method is developed to correct the vertical displacement of the IP produced by the secondary growth of the roots and to avoid overestimation of the rates. The study was carried out in three representative hillsides of Dehesa located in the Buitrera and Parapuños farms (province of Cáceres). Average vertical displacement of the IP was 10.2 cm. The erosion rates reported by the 137Cs technique were similar to those obtained with the IP method: 29.3 t·ha-1·y-1 and 27.3 t·ha-1·y-1 in Buitrera and, 28, 0 t·ha-1·y-1 and 26.7 t·ha-1·y-1 in Parapuños, respectively. During the 17th, 18th and first half of the 19th century erosion rates were very low in both farms (0 t·ha-1·y-1). In Buitrera, from the second half of the 19th century onwards the rates amounted to 7.4 t·ha-1·y-1 and, from the 20th century reached values close to 30.0 t·ha-1·y-1. In Parapuños, erosion rates increased at the end of the 19th century, with a rate of 18.0 t·ha-1·y-1. Soil erosion rate increases throughout the last centuries were presumably related with an intensification of land use, such as cultivation and excessive stocking rates of domestic animals. Factors such as bare soil and the flow power to erode influenced the spatial variation of the erosion rates (R2=0.76).