Ecological study
For each new process domain reach, we identified all vascular plants in
the riparian zone between the summer low water mark and the edge of the
riparian zone (as defined by the dominance of Vaccinium myrtillus(bilberries)). The identification of plant species followed the taxonomy
in Krok and Almquist (2013). In the following cases, two or more species
were treated as one taxon: Carex juncella + Carex nigra ,Callitriche spp. (difficult to identify in the absence of floral
characters), Hieracium spp., Taraxacum spp. (apomictic),Sparganium spp. (common with hybrids). All vegetation inventories
took place in June-August 2016. For large lakes, we only inventoried
riparian plants found in the first and last 300 m along the shoreline.
We calculated richness (number of species) and species density for each
reach/lake and determined community composition. We used regression
analyses to study the relationship between changes in species density
and richness with geographical distance downstream. We also examined
whether there were relationships between community similarity, using
Jaccard’s index, and distance between reaches to determine whether
hydrochoric dispersal is a potential control on riparian metacommunity
organization. All statistical analyses were performed in R studio
version 3.6.0 (R Core Team, 2021).