A study on Douro vegetation

Different classification and ordination techniques were used to study the natural vegetation of Douro region. Polar ordination (PO) , principal components analysis (PCA), reciprocal averaging (RA), detrendend correspondence analysis (DCA) were the ordination techniques used. Grouping of samples by dominance of the different Quercus sp. and two-way indicator species analysis (TWINSPAN) were the classification systems used. Comparison between data records was made with TWINSPAN leading to the conclusion that there is no major difference in classifications based on presence-absence and quantitative data. Results arising from the data including only trees and that considering both trees and shrubs were not very different. Comparison of the several ordination techniques has been made in terms of the ecological meaning of its axes. PO was not so good as PCA and RA, and DCA was the best one. In the classification by TWINSPAN, Quercus rotondifolia and Quercus pyrennaica characterize two very distinct groups. The first group can be subdivided according to the existence of Olea europea (community 1) or Arbutus unedo and Quercus suber (community 2). The second group includes two different communities : community 3 is characterized by Arbutus unedo, Quercus suber and Quercus robur and community 4 is typical of abundant Quercus pyrennaica. Environmental gradients were studied, and precipitation was determined to provide a fairly good explanation of vegetation distribution. Elevation represents another gradient, and should be considered separately in the ecological interpretation of Douro climacic vegetation.