Intrapopulational size structure of the monocarpic species Saxifraga mutata and its relationship to succession

Abstract

Summary The monocarpic Saxifraga mutata, a locally endangered species in Central Europe, grows at sites which are strongly influenced by erosion. Three populations of S. mutata were investigated in Northeastern Switzerland. Each of the localities is characterized by a succession series from almost bare slopes to sparse Pinus-woods (Molinio-Pinetum). Rosette diameters of vegetative and generative individuals showed L-shaped distributions in two populations. A normal-shaped distribution, indicating low rejuvenation, was found in the third population. Rosette diameters were significantly correlated with other fitness-related traits such as number of flowers, number of leaves, and flowering stem length. A reproductive threshold size of c. 4 cm in rosette diameter was recorded. Investigations of size structures in plots of 1 m2 demonstrated that rosette size, rosette density, recruitment, and frequency of flowering individuals were closely related to successional stages as well as intensity and frequency of erosion. Maintenance of local populations of S. mutata depends on the balance between erosion and succession. Landscape dynamics must be warranted in order to conserve this species.