Protection et prolifération : deux notions antagonistes ? : exemple de la Renoncule peltée (Ranunculus peltatus) dans la réserve de biosphère Vosges du Nord-Pfälzerwald

Streams of the Northern-Vosges-Pfälzerwald Biosphere Reserve are proposed to the NATURA 2000 European network. They indeed correspond to the habitat “Floating vegetation of Ranunculus in highland and lowland streams”. Ranunculus peltatus is a determinant species of this habitat and is specially present in this area. Its dynamics was studied on a 10 year-period. R. peltatus has only colonized two new sites. Its abundance has however increased in mesotrophic and eutrophic sites. In sites where it is present, the cover percentage of the other species of the groupment was similar for oligotrophic sites, decreased for mesotrophic sites and increased for eutrophic sites. In mesotrophic sites, several species and especially two protected ones have disappeared. Thus, the protection of this habitat may need the management of R. peltatusProposés au réseau NATURA 2000, les cours d'eau de la Réserve Vosges du Nord-Pfälzerwald abritent un habitat d'intérêt communautaire « végétation flottante de Renoncules des rivières submontagnardes et planitiaires ». Ranunculus peltatus, espèce déterminante de cet habitat, y est particulièrement représentée. Sa dynamique a été étudiée sur une période de 10 ans. R. peltatus a seulement colonisé deux nouveaux sites. Cependant son abondance a augmenté dans les sites mésotrophes et eutrophes. Dans les sites à R. peltatus, le recouvrement des principales espèces constitutives du groupement est resté stable pour les sites oligotrophes, a augmenté pour les sites eutrophes et a régressé pour les sites mésotrophes. Dans ces derniers, plusieurs espèces dont deux de fort intérêt patrimonial ont disparu. Ainsi, la protection de l'habitat à Renoncule peltée peut nécessiter la mise en place d'un contrôle de la dynamique de cette espèce

Suivi biologique par les macrophytes aquatiques de la qualité des cours d'eau de la réserve de biosphère Vosges du Nord-Pfälzerwald

The streams of the Man and Transboundary Biosphere Reserve of the Northern Vosges- Pfälzerwald were subjected to human activities. A monitoring of the water courses and of aquatic plants in 1995 and in 2000 showed an increase of the water trophic level and a decrease of rare protected species. The abundance of populations of the two Elodea species introduced in XIXth and XXth centuries increased in 2000. These two species have a high ability to store phosphorus, which alters ecosystem processes. A new monitoring of the streamwater will be set up to measure the biodiversity loss and the maintenance of our lifesupport systemLes cours d'eau de la Réserve de Biosphère des Vosges du Nord-Pfàlzerwald sont très sensibles aux perturbations. Un suivi de la qualité de l'eau et des espèces végétales en 1995 et 2000 a montré une amélioration du niveau trophique des cours d'eau, mais une régression des espèces protégées suite à la dégradation de la qualité de l'habitat. La surface de recouvrement des herbiers d'élodées, espèces introduites aux XIXe et XXe siècles, tend à augmenter en 2000. Ces espèces sont capables de mobiliser/relarguer des quantités élevées de phosphore dans leurs tissus, ce qui modifie le fonctionnement des cours d'eau. Un observatoire de la qualité des cours d'eau sera constitué afin d'étudier les risques d'érosion de la biodiversité et ses conséquences sur le maintien des écosystèmes

Toward an objective perception of biological invasions

This short note is a summary of a session addressing the "ecological and socio-economical consequences of species introduction" which was run within the French Symposium "Ecologie 2010" (Montpellier, 2-4 September 2010). Scientists attending this session of the symposium recognized the necessity of more objective, more detailed and contextualized analyses of biological invasions. There is need for disentangling the effects from causal processes (e.g. disturbance, pollution) which can drive an invasion. We also have to consider that invasive species may have positive or negative effects, or even both, regardless of our immediate perception of them. The debate addressed the moral values attached to biological invasions and which have to be considered in an ecological as well as a societal perspective. More attention from human sciences is expected in this way

Experimental Assessment of the Water Quality Influence on the Phosphorus Uptake of an Invasive Aquatic Plant: Biological Responses throughout Its Phenological Stage

International audienceUnderstanding how an invasive plant can colonize a large range of environments is still a great challenge in freshwater ecology. For the first time, we assessed the relative importance of four factors on the phosphorus uptake and growth of an invasive macrophyte Elodea nuttallii (Planch.) St. John. This study provided data on its phenotypic plasticity, which is frequently suggested as an important mechanism but remains poorly investigated. The phosphorus uptake of two Elodea nuttallii subpopulations was experimentally studied under contrasting environmental conditions. Plants were sampled in the Rhine floodplain and in the Northern Vosges mountains, and then maintained in aquaria in hard (Rhine) or soft (Vosges) water. Under these conditions, we tested the influence of two trophic states (eutrophic state, 100 mu g.l(-1) P-PO43- and hypertrophic state, 300 mu g.l(-1) P-PO43-) on the P metabolism of plant subpopulations collected at three seasons (winter, spring and summer). Elodea nuttallii was able to absorb high levels of phosphorus through its shoots and enhance its phosphorus uptake, continually, after an increase of the resource availability (hypertrophic > eutrophic). The lowest efficiency in nutrient use was observed in winter, whereas the highest was recorded in spring, what revealed thus a storage strategy which can be beneficial to new shoots. This experiment provided evidence that generally, the water trophic state is the main factor governing P uptake, and the mineral status (softwater > hardwater) of the stream water is the second main factor. The phenological stage appeared to be a confounding factor to P level in water. Nonetheless, phenology played a role in P turnover in the plant. Finally, phenotypic plasticity allows both subpopulations to adapt to a changing environment

Biology and ecology of invasive water primrose: implications for ecosystem management

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morphological variations of Myriophyllum heteophyllum, a new invader in French freshwaters

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Morphological variations of natural populations of an aquatic macrophyte Elodea nuttallii in their native and in their introduced ranges.

International audienceIntroduced plant species appear often more vigorous than their conspecifics in the native range. We investigated the morphological variations of Elodea nuttallii (Planch.) St John and its behaviour in its native and in its introduced habitats. We assessed eight morphological traits of 24 populations in the native North America range and 16 populations in the introduced European range. The introduced taxa can be very distinct in their growth form and size from counterparts in their native range. The shorter broaded-leaved phenotype typically occurs in shallow streams, whereas the longer spacer narrow-leaved phenotype occurs in lakes. Larger leaf width and higher number of lateral shoots - when nutrients are not limiting- may enhance plant performance. The European populations grow more vigorously than their American relatives, possibly because of different selection pressures