Seed Rain in High-Altitude Restoration Plots in Switzerland

Seed rain was studied in restoration plots installed in 1985 and 1987, respectively, on an alpine downhill ski run at circa 2,500 m above sea level. The study was initiated in late autumn 1996 and completed in autumn 1998; it included temporal and spatial variation in density per m², as well as alpha diversity (species richness), and species composition of the seed rain versus that of the resident vegetation. This is the first report on post-restoration monitoring of seed rain above the timberline. Seed rain density and alpha diversity varied seasonally, with the first peak occurring immediately after spring snowmelt and the second in early autumn. The density of seed rain varied between plots and years (1,528–1,778 seeds per m² in one plot RPF] versus 1,096–3,557 seeds per m² in another plot RPG]). Total species number per plot was nearly twice as high in RPF as in RPG in both study years. Seed rain totaled 18 species; all but one represented either transplants introduced in restoration or colonizers established in the plots soon after restoration. Distribution of species in seed rain was largely asymmetric and only a few species provided substantial contributions. Composition of species and their respective contribution to seed rain differed between plots and was clearly influenced by performance of some species used in restoration as transplants; together they provided as much as 51% of the total seed rain. The results of the study demonstrate that restoration enhanced increase of species richness as well as seed rain in situ.