Seed bank and plant community composition, Mixed Prairie of Saskatchewan

Abstract

Many range managers have suggested that clubmoss (Selaginella densa Rydb.) negatively alters the composition of seed banks and inhibits the establishment of plant species that decrease under improper grazing management. Alternatively it is possible that soil seed banks contain few seeds of decreaser species and composition of the seed bank is independent of clubmoss. The purpose of this study was to determine the composition and diversity of the soil seed bank in relation to the clubmoss cover and compositional characteristics of plant communities in the Northern Mixed Prairie of southwestern Saskatchewan. Cover of vascular plants was determined and soil seed bank samples were collected in 100 grazed plant communities. Soil seed bank samples were incubated in the laboratory with emerging seedlings being identified to species. Eight percent (SE ± 1.9) of emerging seedlings in the seed bank were decreasers, 73% (SE ± 2.8) were increasers, and 19% (SE ± 2.3) were invaders, indicating regeneration of decreaser species might be limited by low numbers of seeds in seed banks. Clubmoss cover was not correlated (P = 0.32 to 0.98) with species richness, species diversity, density of decreasers, density of increasers, density of invaders, and total seedling densities in the seed banks. Seed banks and plant communities shared few species as indicated by a low similarity index (x̄ = 0.31, SE ± 0.02). Species richness (x̄ = 3.6 species per 102 cm2, SE ± 0.18) and diversity (x̄ = 1.00, SE ± 0.05) of seed banks were poorly correlated with characteristics of the plant communities. Range condition score was positively correlated (r = 0.17, P = 0.09) with total seedling densities in the soil seed bank, indicating more seedlings can potentially develop from the seed bank with increasing range condition of plant communities. We reject the hypothesis that clubmoss negatively affects the composition of seed banks. Mechanically disturbing plant communities to control clubmoss is predicted to lead to plant communities that are dominated by increasers and/or invaders. Managing for production of seeds by desired species should be a priority in promoting establishment of desired species.