Response surfaces of plant species along water-table depth and pH gradients in a poor mire on the southern Alps (Italy)

Response surfaces along gradients of water-table depth and water pH were obtained for the commonest vascular and bryophyte species in a nutrient-poor mire on the southern Alps of Italy. Depth to the water table was the major factor, whereas the chemical gradient was of lower importance in structuring vegetation. The distributional pattern of vascular plants is considered to be determined by physiological tolerance along the gradient in depth to the water table. Hence, interspecific competition in the field layer is considered of minor importance, except for interactions between ericaceous shrubs. Bryophytes probably interact to a greater extent, especially in lawns and carpets. Sphaghum species appear to be better competitors, as they almost totally exclude other mosses from those habitats. Interactions between species mainly result in dominance patterns, rather than in a clear habitat partitioning along the water-table gradient. Strong dominance by single species rather than clear hab...