Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps rivers

Erosion control of riverbank is frequently necessary to protect human investments situated along rivers. The technique chosen for such erosion control construction may have major impacts on biodiversity and on the functioning of river corridors. Even if there is agreement, that biodiversity should be one criterion for choosing embankments techniques little is known about whether such techniques can accommodate biodiversity. We aimed to determine coleopteran and plant taxonomic diversities along a naturality gradient of riverbank protection systems, ranking from entirely civil engineering structures, through combined constructions (mixing civil engineering and bioengineering), to purely bioengineering structures. Fifteen sites (five sites of each technique) were sampled in the Rhône-Alpes region (S.E. France). On each site, vegetation was sampled along three transects from the bottom to the top of the riverbank and flying beetles by trapping. In total, we recorded 148 plant species and 78 beetle genera. We found significantly lower animal and plant diversities within civil engineering constructions than in the other two techniques. Diversities of both techniques tended to be higher, although not significantly, in combined techniques than in purely bioengineering ones. Furthermore, civil engineering structures were more subject to invasion by exotic plant species than the two other techniques. These results quantify and highlight the interest of bioengineering techniques compared to civil engineering in enhancing biodiversity and limiting invasive species techniques

Growth response of cuttings to drought and intermittent flooding for three Salix species and implications for riverbank soil bioengineering

Willows are used as cuttings or in fascines for riverbank soil bioengineering, to control erosion with their high resprouting ability and rapid growth. However, water availability is highly variable along riverbanks both in time and space and constitutes a major stress limiting willow establishment. A species-specific understanding of willow cutting response to water stress is critical to design successful riverbank soil bioengineering projects given exclusive use of local species is often recommended. In a three-month greenhouse experiment, we investigated the effects of three soil moisture treatments (drought—soil saturation—intermittent flooding) on survival, biomass production and root growth of cuttings of three willow species used for soil bioengineering along NE American streams (Salix discolor—S. eriocephala—S. interior). Cutting survival was high for all species and treatments (>89%). Biomass production and root volume only differed between species. S. eriocephala produced the highest biomass and root volume, and S. discolor invested more in belowground than aboveground biomass. Root length responded to soil moisture differently between species. Under intermittent flooding, S. eriocephala produced shorter roots, while S. interior produced longer roots. For riverbank soil bioengineering, S. eriocephala should be favored at medium elevation and S. interior at lower elevation

Soil and water bioengineering in cold rivers: A biogeomorphological perspective

Soil and Water Bioengineering (SWBE) for river management is a viable alternative to civil engineering when bank stabilization is needed. Unlike riprap, SWBE techniques support bank stabilization while promoting the development of riparian vegetation. The preservation of vegetation biodiversity on riverbanks helps maintain and create essential ecosystem services such as recreation, carbon sequestration, pollutant filtration, and the creation of ecological niches and corridors. However, the potential of SWBE remains largely underestimated. Managers are often reluctant to use these techniques as they present failure risks, particularly in rivers with severe mechanical constraints. In cold environments experiencing freezing waters, ice-related processes such as ice abrasion or ice jams are significant disturbance factors for both river morphology and riparian vegetation. The marginality of SWBE is thus exacerbated in these environments, where considerable knowledge gaps persist regarding the interactions between ice, river channel morphology, and vegetation persistence. This review article aims to discuss the insights that biogeomorphology can provide for SWBE in cold environments. Biogeomorphology, a science that studies the interactions and feedbacks between living organisms and the physical processes shaping the landscape, offers new concepts and models as tools for understanding the co-development between landforms and vegetation. In the scope of SWBE, biogeomorphology can be used to (1) provide a better understanding of a river's dynamics and biogeomorphological changes in time and space to better identify the root causes of degraded riverbanks, (2) identify assemblages of species best suited to local conditions and better understand the relationship between channel morphology, vegetation, and ice to improve SWBE structure design, and (3) develop monitoring and evaluation tools to define the biogeomorphological functions of SWBE structure and improve maintenance strategies

Control of invasive Asian Knotweeds with ecological engineering methods: feedbacks from experimental restoration of invaded riverbanks

Classées parmi les pires espèces exotiques envahissantes de France et d’Europe, les Renouées asiatiques sont en pleine expansion. L’efficacité relative et le coût des techniques de contrôle traditionnelles poussent les praticiens à se tourner vers d’autres solutions. La lutte via la restauration d’une ripisylve pérenne a fait l’objet de nombreux essais. Il s’agit le plus souvent du bouturage de Saules ou de la plantation de jeunes arbustes sur des taches de Renouées asiatiques, associés ou non à un prétraitement (fauche, arrachage ou pose de géotextile). Le présent article se propose de discuter de l’efficacité de ces méthodes à la lueur d’expérimentations menées de 2011 à 2014. Dix placettes expérimentales ont été installées pendant l’hiver 2011-2012 afin de tester l’efficacité du bouturage de Saule des vanniers pour le contrôle des Renouées asiatiques. Une partie de ces placettes a fait l’objet d’un décaissement de surface et des fauches ont été pratiquées. Depuis 2012, un suivi régulier des Saules et des Renouées asiatiques est effectué. Au niveau des Saules, en dehors de problèmes d’herbivorie par les Ragondins, leur croissance rapide a permis d’obtenir un couvert végétal recouvrant les Renouées à partir de la deuxième ou de la troisième année, permettant ainsi de supprimer les fauches sur certaines placettes. Ces résultats prouvent qu’il est possible d’implanter de façon pérenne une espèce compétitrice au sein d’un espace infesté par les Renouées. Le décaissement préalable n’a pas d’effet très sensible sur le succès des Saules vis-à-vis des Renouées. Ce retour d’expérience montre que la restauration d’une communauté végétale arbustive peut réduire significativement la vigueur des Renouées asiatiques. L’abandon de certaines placettes en raison d’une forte pression des Ragondins ainsi que les différences observées sur le rythme de croissance des Saules, témoignent du caractère multifactoriel de la réussite de ce type d’ouvrage de génie écologique. Ces résultats illustrent également les effets de facilitation qu’il peut y avoir entre espèces invasives (ici entre Renouées asiatiques et Ragondins)Considered among the 100 worst invasive species in the world, Asian Knotweeds are spreading in France and Europe. Asian Knotweeds are mostly found along riverbanks, which represent a big issue as these habitats are considered as ecotones and welcome a high biodiversity. The poor efficiency of traditional management methods drives managers to find alternative solutions. Knotweed control through the restoration of a riparian plant community has raised interest and numerous essays have been conducted since these 15 last years. Based on ecological engineering methods, they consist in planting Salix cuttings or young seedlings on Knotweed patches. Successes and failures can be observed but no explaining factors are known. This article aims at testing the efficiency of such methods in the light of ten experiments followed from 2011 to 2014. Ten experimental works have been put in place in order to test the efficiency of ecological engineering methods to control Asian Knotweeds. Cuttings of a pioneer riparian species, Salix viminalis, have been planted during winter 2011-2012 in order to enhance the development of a competitive plan cover. Rhizomes from half of these experiments have been extracted and exported in order to reduce Knotweed underground biomass. Survival and growth of Salix cuttings were facilitated through regular mowing. Vegetative height was measured twice a year from 2012 to 2014 on Salix and Knotweeds. Out of problems with Coypu, high Salix growth allowed a dense vegetal cover to overgrow Knotweed canopy after two or three years. Mowing could even be stopped on some experimental works. These results show that it is possible to plant a competitive species on Knotweed stand. Data measured on Knotweeds reveal noteworthy effect on their performance. Rhizome extraction has no significant effects on Salix success over Knotweeds. Our results are encouraging as they confirm the potential of restoring a native competitive plant cover to control Asian Knotweeds. Coypu impacts and differences observed on Salix growth reveal that success of such methods is multifactorial. From a theoretical point of view our experiment illustrates the invasive legacy as Coypu could facilitate Knotweed invasio

Réponse du peuplier noir (Populus nigra L.) aux contraintes hydrogéomorphologiques : une expérimentation ex situ semi contrôlée

International audienceBased on the hypothesis of an eco-evolutionary feedback between woody riparian species and fluvial geomorphology, a semi-controlled ex situ experiment has been planned to quantify key response functional traits (morphological and biomechanical) of Populus nigra L. cuttings to simulated hydrogeomorphological constraints, as well as to dissociate the specific responses to them. The constraints tested are sediment burial and drag force exerted by floods. The characteristics of the experiment are presented as well as the experimental design. The hypothesis of a positive niche construction by P. nigra is tested to a certain degree. The results from this research will improve our understanding of riparian ecosystem functioning and specifically of the role of this key woody pioneer species within active floodplain rivers.Basé sur l’hypothèse d’existence d'une rétroaction éco-évolutive entre les espèces végétales riveraines ligneuses et la géomorphologie fluviale, une expérimentation ex situ en conditions semi-contrôlées a été planifiée afin de quantifier les traits de réponses fonctionnels (morphologique et biomécanique) de boutures de Populus nigra L. soumises à des contraintes hydrogéomorphologiques simulées : l’enfouissement sédimentaire, la force de traînée, et la combinaison des deux contraintes. Les questions scientifiques et le protocole expérimental sont présentés ici. L’hypothèse d’une construction de niche positive de P. nigra est testée à un certain degré. Les résultats de cette recherche contribueront à améliorer notre compréhension du fonctionnement des écosystèmes riverains et plus particulièrement du rôle de cette espèce ligneuse pionnière clé au sein de la bande active des cours d’eau

Bringing the margin to the focus: 10 challenges for riparian vegetation science and management

Riparian zones are the paragon of transitional ecosystems, providing critical habitat and ecosystem services that are especially threatened by global change. Following consultation with experts, 10 key challenges were identified to be addressed for riparian vegetation science and management improvement: (1) Create a distinct scientific community by establishing stronger bridges between disciplines; (2) Make riparian vegetation more visible and appreciated in society and policies; (3) Improve knowledge regarding biodiversity—ecosystem functioning links; (4) Manage spatial scale and context-based issues; (5) Improve knowledge on social dimensions of riparian vegetation; (6) Anticipate responses to emergent issues and future trajectories; (7) Enhance tools to quantify and prioritize ecosystem services; (8) Improve numerical modeling and simulation tools; (9) Calibrate methods and increase data availability for better indicators and monitoring practices and transferability; and (10) Undertake scientific validation of best management practices. These challenges are discussed and critiqued here, to guide future research into riparian vegetation

Les techniques de génies végétal pour la protection des berges de rivières : répondre aux défis de la gestion durable dans un monde changeant

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVINInternational audienceLes techniques de génies végétal pour la protection des berges de rivières pour répondre aux défis de la gestion durable dans un monde changeant

Les techniques de génies végétal pour la protection des berges de rivières : répondre aux défis de la gestion durable dans un monde changeant

International audienceLes techniques de génies végétal pour la protection des berges de rivières pour répondre aux défis de la gestion durable dans un monde changeant

Dynarp : dynamique paysagère des renouées sur les infrastructures de transport

National audienceDynarp : Dynamique paysagère des renouées sur les infrastructures de transport