Ecological Ordination and Distribution of Hygrophilous Species Growing on a Mediterranean Riverbank (SW Spain)

The Guadiamar riverbanks are home to riparian plant communities, such as alder, poplar and ash forests, tamujares, salt marshes, reed beds, etc. characteristic of Mediterranean rivers. A data set of these communities, including floristic relevés and environmental variables (physical and chemical soil properties, bioclimate) was analysed to correlate their floristic composition/species distribution with environmental variables. By means of an RDA (redundancy analysis) and a complementary cluster analysis four groups of species were discriminated according to their ecological requirements. The RDA displayed three major, parallel-running gradients (i.e., textural, bioclimatic and chemical) in environmental variables. Other less conspicuous, crossed gradients revealed the impact of man-made alterations, particularly in the middle reaches of the river. The results can be helpful in the planning of future ecologically oriented restoration programmes of wetlands.