Restauration de la flore des prés salés continentaux : expérimentation sur le marais de Saint-Beauzire (Puy-de-Dôme, 63)

Cet article présente une étude de cas de recolonisation par la végétation de type pré salé continental après des travaux de suppression d’un remblai sur un marais salé continental dans la plaine de la Limagne (Puy-de-Dôme, France). Les plantes indicatrices des prés salés ont été suivies en présence/absence dans un réseau de 104 mailles de 10 m². Nous avons pu montrer la colonisation rapide et durable de Puccinellia distans et Juncus gerardi, mais aussi l’installation plus lente et variable de Spergula media et de Plantago maritima. Nous avons cartographié les évolutions spatiales et temporelles de cette colonisation pour 6 espèces différentes. Parmi les espèces halotolérantes, on notera l’augmentation de la population d’espèces menacées comme celle d’Inula britannica. Les résultats permettent de conclure sur l’intérêt de ce type d’opération de suppression de remblais pour restaurer les paramètres abiotiques et de la capacité de la flore de se réinstaller même après vingt-cinq ans pour reconstituer une communauté végétale caractéristique des « prés salés continentaux ».

Conditions de germination et rôle des herbivores dans la dispersion et le recrutement d'une espèce clonale : Juncus gerardi Lois.

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°C but null for a 0-10°C 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.Key words: germinative capacities, feces, clonal plant, grazers, endozoochory, pastures.

Variations in marsh surface levels in the upper Tay Estuary

SynopsisIn the upper Tay Estuary the marshes bordering the northern intertidal mud-flats are dominated by Phragmites communis in the west, with Juncus gerardi becoming more important eastwards, where Aster tripolium is also significant. Sedimentation on the surface of the marshes at Kingoodie and Invergowrie has been measured at monthly intervals over a twenty-three month period, using stake implants to provide local marker levels. The marsh surfaces were at their greatest heights in early summer and fell during autumn and winter. Maximum accretion rates were measured in spring on the outer marshes at both sites, where net accretion over the entire period was greatest. The net accretion in the Phragmites marsh was 2.5 mm, in the Aster belt 5 mm, in established Juncus 9 mm and in newly colonising Juncus 8.7 mm, whereas on the adjacent Kingoodie mud flats there was net stability over the twenty-three-month interval. Accretion was less at Invergowrie (3–5 mm) than at Kingoodie (2.5–9 mm). Monthly analysis of the upper 0.5 cm of the surface sediments showed the Invergowrie marsh sediments to be sandier than those of Kingoodie. Silts and clays deposited on the outer marsh surface in spring migrate landward during the summer and autumn. The apparent annual net accretion varied greatly with the specific month used for comparison, with 13 mm net losses based on November figures and 10 mm gains using January data.