The dispersal capacity of vegetative propagules of riparian fen species

Abstract

Flowing water can disperse a high number of seeds and vegetative propagules over long distances and is therefore a very important dispersal vector in wetland habitats. Although the dispersal of seeds is relatively well studied, the dispersal of vegetative propagules has received less attention. However, in riparian and aquatic systems where many species have clonal growth forms, it can be very important. The relative importance of vegetative propagules in the dispersal of fen species was assessed first by determining their relative abundance in the field and second, by determining the buoyancy of plant fragments of ten fen species experimentally. On average, vegetative propagules made up 3.2-58.9% of the total propagule number (mainly Elodea nutallii). Buoyancy of the tested species ranged from 25 days to over 6 months. Surprisingly, the propagules of Stratiotes aloides and Hydrocharis morsus-ranae increased buoyancy when spring started (after ca. 100 days). The results demonstrate that vegetative propagules of riparian and aquatic fen species have a high capacity to disperse over long distances via water and are therefore likely to play an important role in the colonisation of new habitats. Especially because in nine out of the ten species tested, over 50% of the propagules were still viable after 6 months of floating.

Multiple effects of land-use changes impede the colonization of open water in fen ponds

“…We did not find any clear evidence for wave damage, as effective fetch was small (<100 m) and did not relate to colonization success in our factor analysis. However, species richness was highest in sheltered sites, which is in accordance with a previous study showing that germination and establishment of colonizers are highest in sheltered shorelines (Sarneel 2010).…”

“…Therefore, sod cutting could be an effective measure to reduce nutrient concentrations in the bank. The risk of removing a valuable seed bank together with this topsoil is low, because many of colonizers are absent in the seed bank (Sarneel 2010). However, populations of colonizer species on the banks that could function as a source of propagules are, for this same reason, of great importance and should therefore be left intact.…”

“…To improve water quality, measures that decrease nutrient concentrations in agricultural run‐off, decrease the supply of river water and, more locally, increase hydrological isolation have already been shown to be effective. It should be noted, however, that hydrological isolation of individual ponds will decrease the probability of dispersal, a factor that should not be totally ignored (Sarneel 2010). A detailed analysis of all measures that potentially increase water quality is given in Lamers et al (2010).…”

“…To receive propagules via water, connections with other water bodies are needed and, therefore, we counted these in each pond. Further, as dispersal follows the prevailing wind direction (Sarneel 2010), the geographical orientation of these connections in relation to the prevailing wind direction (SW) is of importance. For this, we classified the ponds into four categories: 0 – isolated (ponds with no connections); 1 – low probability of seed supply (ponds with connections, but not in the SW side of the pond); 2 – some probability of seed supply (ponds with connections in the SW side of the pond, but connected to a ditch perpendicular to the prevailing wind direction, limiting transport through that ditch); 3 – high probability of seed supply (ponds with connections in the SW side of the pond and connected to another SW‐oriented water body).…”

Biology of invasive alien plants in Canada. 13. Stratiotes aloides L.

“…In a fen wetland, plantlet dispersal was most effective in deep water with S. aloides a dominant colonizer species (Sarneel et al 2011). Buoyancy increased rapidly in the spring, remaining as high as 92% after 187 days, and 84% resprouted after dispersal (Sarneel 2013).…”