Primary succession over sixty years on hundred-year old islets in Lake Hjälmaren, Sweden

Abstract

New islands were created as a result of an artificial lowering of the water table of Lake Hjälmaren in 1882–1886 and the floras of 40 such islands have been monitored ever since plant colonization started in 1886. Data used in this paper are from belt-transects across ten of these islands which were analysed in 1927 – 29 and reanalysed in 1986. During this 60-year period shading by trees has increased and shading and litter accumulation have affected the ground flora. Succession includes aspects of both convergence and divergence. Species of dry, open sites and shore species have been excluded from the island interiors, making these parts of the islands more similar, but there has simultaneously been an increased variability of vegetation types of shaded, mesic habitats. There have been no consistent trends in beta-diversity between the two surveys. Differences in successional patterns between island interiors and shore habitats are attributed to an outward migration of plant species and to differences in disturbance regimes.

Nomenclature

Krok, Th. O. B. N. & Almquist, S., 1984. Svensk Flora, fanerogamer och ormbunksväxter. 26th ed., rev. L. Jonsell & B. Jonsell. Esselte Studium, Uppsala, for vascular plants; Nyholm, E., 1954–1969. Illustrated moss flora of Fennoscandia. II. Musci. Swedish Natural Science Research Council, Stockholm, for mosses.