Plant communities partially refl ect environmental gradients in humanized landscapes: a case study in the Llobregat delta marshes

This study took place in a vegetation mosaic of the Llobregat delta (near Barcelona, Spain), which includes both natural and spontaneously restored coastal marshes. We used a dataset comprising vegetation relevés, soil parameters and water table conditions, and explored their correlation. More precisely, we classifi ed the relevés into three phytosociological alliances (namely Phragmition communis, Salicornion fruticosae and Juncion maritimi) combining the previous information available and the use of PCA ordinations. We studied whether these alliances refl ect the main operating environmental gradients (conductivity, sodium absorption rate and water table dynamics) using a GLMM (generalized linear mixed model). The PCA refl ected a fair distinctiveness of Salicornion and Phragmition, whereas Juncion was a more heterogeneous unit, related to the varying dominance of different plant species. The three alliances exhibited signifi cant differences in environmental variables and therefore the phytosociological ordination refl ected at least partially the main operating environmental gradients. However the assemblage of alliances over the gradients varied between locations, suggesting that the initial species pool or plant dispersal capacity to some extent shapes the dynamics of spontaneous restoration in these marshlands.