Vegetation diversity of mesic grasslands (Arrhenatheretalia) in the Iberian Peninsula

Abstract

AbstractQuestionsWhat is the diversity and main vegetation types in mesic grasslands on the Iberian Peninsula? What are the main diagnostic species of each type? What are the main environmental gradients that drive patterns of species composition? To what extent does biogeography influence community diversity?LocationIberian Peninsula (Portugal and Spain, including the French Pyrenees).MethodsFormal definitions based on the Cocktail method were used to establish a typology of mesic grasslands of the Arrhenatheretalia order. This method was applied to a stratified data set of 3485 relevés, also including other types of perennial grassland. Semi‐supervised classification based on the K‐means algorithm was used to assign almost 757 relevés into the vegetation types defined by Cocktail and to identify new ones. The types were compared by means of detrended correspondence analysis (DCA) using climate data, altitude and Ellenberg indicator values as explanatory variables.ResultsFourteen ecologically well‐defined associations were distinguished in the Arrhenatheretalia order: five in the Arrhenatherion alliance, two in Triseto‐Polygonion and seven in Cynosurion. Soil reaction, summer aridity and altitude were identified as the most important determinants of species composition. These lithological and bioclimatic gradients are related to the biogeographic diversity of the study area, which is the main driver of community diversity in Arrhenatheretalia grasslands; it is more important than the management practices expressed in the concept of alliances. The classification and ordination analyses also showed a clear differentiation in community diversity according to biogeographic sectors (eastern Cantabrian‐Atlantic, Galician‐Portuguese, Carpetan‐Leonese, Pyrenean, Orocantabrian/western Pyrenean and Oroiberian/Catalan‐Valencian). In addition, moisture and nutrient content were more important than altitude in differentiating Arrhenatherion and Triseto‐Polygonion communities in the Pyrenees.ConclusionsWe suggest a simplification of the traditional classification of the Iberian Arrhenatheretalia grasslands. For this revised classification, we propose an electronic expert system with consistent rules for assigning vegetation observations to the associations defined, and a list of the diagnostic species of each vegetation type. These results can be applied to identify and monitor the hay meadows included in Annex I of the European Habitats Directive, taking into account the biogeographic context of the indicator species.