• Litter powder;
  • Northern Sweden;
  • Plant trait;
  • Riverborne litter
  • Tutin et al. (1964–1980);
  • Mossberg et al. (1992)

Abstract. The floristic effects of river-borne litter that accumulates in riparian zones may vary in space and time depending on variations in mass and particle size of the deposited litter. To analyse the effects of litter mass and size we applied differentsized litter (natural uncut pieces and powder) to riparian vegetation at different quantities. Vegetation responses were analysed after one season at the community level (total biomass or richness for all species) and species traits (biomass or richness for groups of species). At the community level uncut litter, but not powder, reduced species richness and both uncut and ground litter reduced above-ground biomass. At the species trait level uncut litter had a stronger effect than powder on species richness and biomass. The only positive effect of litter addition was that powder increased graminoid species richness. The topsoil conditions indicated that the major impact of deposited, river-borne litter was that it acted as a physical barrier directly preventing established plants from penetrating the litter layer and reducing light and soil temperature.