The finding of new individuals of a clonal plant, Juncus gerardi, raised the question of modalities for the colonization of new sites by this species. Indeed, the existence of seedlings has not been observed in the field, nor reported in the literature for European marshes. Among the parameters limiting recruitment, we examined the soil seed bank, which appeared extremely small. Many seeds could be found in bovine feces but few were found in equine feces. Futhermore, bovines are not only important for seed dispersion, but also for the improvement of the germinative capacities: the seed germination rate of Juncus gerardi was doubled after digestive transit. Germination testing showed that this species is largely tolerant to salinity (from 0 to 26,4 mS.cm(-1)). The germination rate was maximal with a thermoperiod of 10-20 degreesC but null for a 0-10 degreesC thermoperiod. Germination was improved by immersion and was light dependent. The critical phase for colonization success in new habitats could be primarily seedling survival. Recruitment success in Juncus gerardi seems to be a rare event, requiring the combination of favorable conditions related to climate and gap openings in swards.
