Spatial distribution and temporal dynamic of the seed pool in a Danish lowland stream

In this paper we quantify the seed pools in four locations down through a small stream in Denmark. The objectives of the study were (1) to test if the number of plant taxa in the seed pool increases downstream in the stream system; (2) to test if the seed density in the pool is highest in autumn; and (3) to analyze to what extent the seed pool contributes to re-establishment of vegetation in spring. Counting method showed no increase in species taxa in the seed pool down through the stream system. Neither did we find clear seasonal patterns in seed abundance in the seed pool. By concurrent field and laboratory observations in spring we found that seed pools can function as a source for re-establishing the vegetation in spring. However, the actual germination rate in the field was <100 and <10 times the germination rate in the laboratory for aquatic and terrestrial plants, respectively. The results suggest that small lowland streams contain large seed pools in deposition areas throughout the year, and that seed pools are much more important for the re-establishment of riparian stream vegetation in spring than submerged vegetation.

Research highlights
► Number of plant taxa in stream seed pools does not change downstream in lowland stream system.
► Seed density is high and does not change predictably with season in lowland stream.
► Seed pool contribute to reestablishment of vegetation on the banks in spring, but to a much lesser extent in streams, even though the seed pool is present.