Warm-Temperate Forests of Central Portugal: A Mosaic of Syntaxa

Despite extensive afforestations with allochthonous tree species, the Atlantic façade of the mountain chain that extends through central Portugal still presents several examples of autochthonous forests that show significant floristic and ecophysiological diversity. Along a N-S transect of no more than 100 km along this range, zonal forest types may vary from semi-deciduous Quercus robur formations with evergreen understory (Viburnum tinus or Arbutus unedo) to marcescent Quercus broteroi forests and sclerophyllous forests of Quercus suber. Adding further diversity to the vegetated landscape are extrazonal groves of non-sclerophyllous evergreens like Prunus lusitanica, Ilex aquifolium, Rhododendron ponticum, Laurus nobilis and Myrica faya, relicts of the Tertiary laurisilva. While data suggest that a macrobioclimatic gradient (from temperate to mediterranean) may be responsible for such a variety of forest formations, a convoluted set of orographic, edaphic, hydrologic, microclimatic and paleohistorical factors certainly contributes to explain the variation in this peculiar region. This study compares these plant communities of central Portugal, classified according to Braun-Blanquet methodology. We studied the number of relict species present in each community, as well as the laurophyllous taxa that had become adapted to the present climatic conditions. Extrazonal groves showed the greatest percentage cover by relict species, while zonal forests contained more newly adapted laurophyll species. Among the zonal forests, those dominated by Quercus robur in warmer areas had the highest percentage covers of relict species. Finally, we propose the new syntaxon Asparago aphylli-Quercetum suberis lauretosum nobilis.