Species and life-forms composition of Mediterranean mountain pastures in two years of contrasting precipitation

Abstract

Summary Twenty sites, representing different pasture types in NW Spain, were sampled with respect to their floristic composition and structural characteristics for two years of contrasting precipitation. The first year was characterised by a severe regional drought and the second year had normal precipitation. Four plant community types were identified by consensus classification techniques of plant species composition. These community types were associated with grazing regime, percentage cover of herbaceous vegetation, rocks and bare ground, and soil characteristics. One community type included mesic sites on acidic parent materials with low grazing, whereas the other three were all intensely grazed, and included either xeric or mesic sites on calcareous parent materials, or mesic sites on acidic parent materials. Species composition varied between years according to well defined directional trends within the intensely grazed communities. Compositional differences between calcareous and acidic pastures increased in the normal year. On average 49 to 73% of the species appeared only in one year. This high species turnover was also high when analysed separately for different life-forms, namely annuals, perennial grasses, perennial forbs and undershrubs. In spite of this, both the life-form spectrum, and the relative abundance of each life-form remained unaltered for each community type in both years. This suggests that such characteristics of the communities' structure are in equilibrium with habitat characteristics, as well as the existence of a deterministic structure in the grasslands studied.