The Dehesa: Does this Complex Ecological System Have a Future?

Abstract

The dehesas of the south-western Iberian Peninsula are "man-made" ecosystems characterized by a savanna-like physiognomy. The open tree stratum is dominated by three oak species, Quercus ilex, Q. suber and Q. pyrenaica, whose densities range from 10 to 80 trees per hectare. In this paper, the key processes involved in the agro- ecological function of the dehesas are discussed, with particular reference paid to the significant modifications of environmental conditions induced by the presence of isolated trees. I describe how, in the face of the physiological constraints imposed by climatic stress, the changes in soil properties caused by the presence of trees increases the availability and uptake of soil water and permits a more efficient use of the limited water resource by the vegetation. Finally, the key aspects of future research that need to be addressed in order to improve our understanding of the functional ecology of the dehesa ecosystem are proposed.