The Alpine vegetation of the Pyrenees, a contrasting assemblage of plant communities, life strategies, and biogeographic sources

Abstract

The alpine vegetation is frequently characterized as landscape mosaics where contrasting plant communities in terms of species composition and functional structure are set responding to abrupt changes through rough physiography. In this paper, we analyse the vegetation of the alpine belt of the Catalan and Andorran Pyrenees combining its phytosociological description with the assessment of functional plant traits. Our aim is to build a comprehensive framework for analysing the relationship between plant cover and environment, and thus for understanding plant diversity through the varying alpine landscapes. For this purpose we used 800 releves gathered in a vegetation databank which have been classified into 46 community-types (associations). Then we have characterized the associations assessing the most frequent plant species by means of a wide scope of traits, summarized at the releve level, and then at the association level. Most of the community-types assessed reflect the distinct stressing conditions found in alpine environments. In dense grassland types, however, better ecological conditions (fair soils, gentle reliefs) are evidenced by higher competitive ability and above-ground turnover of the dominant species. These community-types show moderate diversity in terms of plant functional types and particular species. More stressing conditions give way to poorer community-types, because only a few specialized plants can thrive in one or another distinct habitat. However, this vegetation includes more singular species in the biogeographic aspect (i.e., endemics) and also as plant functional types (e.g., succulents, small cushions, semelparous). A particular vegetation group, the alpine heaths, reflect the local fitness of a few woody species able to drive the rest of plant community and the ecosystem functioning. There is still a lack of knowledge on the actual effect of grazing on the relative role played in contemporary landscapes by alpine heaths and grasslands.