The vegetation in the Villuercas region (Extremadura, Spain) and in Serra de San Mamede (Alto Alenteio, Portugal). The effect of different land use on the vegetation pattern
Orellana, Joséalfredo Vicente; de Mera, Antonio Galán
The effects of different agricultural regimes on the mosaic of plant communities and the dynamics of the landscape are analysed: smallholdings in Alto Alenteio (Portugal) and latifundia in Extremadura (Spain). The Spanish area is located in the Sierra de Guadalupe, in Villuercas. The Portuguese area is located in Serra de S. Mamede, in Alto Alenteio. These two areas selected have identical geology, similar climatic conditions and the same type of climax vegetation (Arbuto unedonis-Querceto pyrenaicae sigmetum, Sanguisorbo agrimonioidis-Querceto suberis sigmetum, and Pyro bourgeanaeQuerceto rotundifoliae sigmetum), but different replacement communities can be observed. The differences have been studied in all types of vegetation, including forests, pastures, crops, roads, trails, irrigation ditches, streets and walls of some villages, and hydrophilous plant communities. Beyond the classical associations, fragmentary vegetation types are also considered (basal communities, derived communities). The mosaic of vegetation types was sampled by SIGMA relevés (15 in Extremadura and 15 in Alto Alenteio, of 1 km2 each one). As a result, "dehesas" are more frequent in Spain than in Portugal, where forests have been cleared for agriculture. Rockrose shrubs (Cistus ladanifer), and heaths (Erica sp.), indicate burnt areas. Generally, Extremadura shows well conserved pastures suitable for livestock grazing (Poo bulbosae-Trifolietum subterranei, Pulicario-Agrostietum pourretii, Gaudinio-Agrostietum castellanae), while in Portugal, subnitrophilous fallow land communities are more variable, due to the more intensive and less mechanised use of soil (Chrysanthemo-Chamaemeletum fuscati, Rumici angiocarpi-Coleostephetum myconis). Roadside communities are clearly linked to their history and influenced by the contact communities. Communities linked to settlements are more diversified in Portugal than in Spain, because stony walls around fortresses and in Jewish quarters (Parietarietum judaicae, Anogrammo-Umbilicetum rupestris), and medieval paved streets with their respective plant communities (Gymnostiletum stoloniferae, Euphorbio-Oxalidetum corniculatae), have been conserved. Riverside vegetation complexes also differ in Spain and Portugal, as a result of different relief features and hydrological conditions. In Extremadura there are wide plains disturbed by the flooding of rivers, with the association Pyro bourgeanae-Securinegetum tinctoriae ("tamujares"); in Portugal, riversides are more abrupt, thus alder (Scrophulario-Alnetum glutinosae) and willow groves (Viti-Salicetum atrocinereae) are more frequent.