Species composition and plant traits: Characterization of the biogeomorphological succession within contrasting river corridors

[EN] Plant communities and dynamics can be characterized according to species composition or plant traits. Here, we used species composition and plant traits to compare their effectiveness in discriminating the biogeomorphological (involving reciprocal feedbacks between physical and biological processes) and ecological (mainly biologically driven) phases of the fluvial biogeomorphological succession (FBS) model. The comparison was done between two French rivers, the largely unchannelized lower Allier and the channelized middle Garonne. One reach representative of each river section was selected for the study. Within each river reach, we chose two contrasted study sites in terms of channel and floodplain dynamics: a reference site (least altered channel and floodplain dynamics) and an altered site (laterally stabilized by riprap and constrained). In the four study sites, we sampled vegetation in 402 plots of 4 m2. The 512 species identified in the plots were characterized in terms of plant traits (20) from a literature review. When comparing reaches in unconstrained ordinations and per mutational multivariate analyses of variance, both species composition and plant traits led to a similar identification of the biogeomorphological and the ecological successional trajectories. Nevertheless, the trait approach was less influenced by local and regional bioclimatic, hydrogeomorphological, and anthropogenic settings and thus produced a more comprehensive and general classification of the biogeomorphological and ecological phases of the FBS model. A lower than expected contrast between the four sites was found, because neither species composition nor plant traits could entirely characterize distinct successional trajectories occurring in our reference or altered sites. Furthermore, our results contributed to a better understanding of the multiple successional trajectories that can occur in midlatitude river corridors. It also showed that relating plant traits to their effects on fluvial landform dynamics remains a core challenge in explaining succession including feedback mechanisms between hydrology, morphodynamics, and vegetation dynamics.French National Centre of Scientific Research; French Ministry of Ecology, Environment, Sustainable Development and PlanningTabacchi, E.; González, E.; Corenblit, D.; Garófano-Gómez, V.; Planty-Tabacchi, A.; Steiger, J. (2019). Species composition and plant traits: Characterization of the biogeomorphological succession within contrasting river corridors. River Research and Applications. 35(8):1228-1240. https://doi.org/10.1002/rra.35111228124035

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

Impacts of biological invasions: what's what and the way forward

Study of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society

Light interception principally drives the understory response to boxelder invasion in riparian forests

Since several decades, American boxelder (Acer negundo) is replacing white willow (Salix alba) riparian forests along southern European rivers. This study aims to evaluate the consequences of boxelder invasion on understory community in riparian areas. We determined the understory species richness, composition and biomass in boxelder and white willow stands located in three riparian forests, representative of three rivers with distinct hydrological regimes. We investigated correlation of these variables to soil moisture and particle size, main soil nutrient stocks, potential nitrification and denitrification, tree canopy cover and photosynthetic active radiation (PAR) at the ground level. A greenhouse experiment was then conducted to identify the causal factors responsible for changes in the understory. The effect of soil type, PAR level and water level on the growth and the biomass production of Urtica dioica were examined. A lower plant species richness and biomass, and a modification of community composition were observed for boxelder understory in all sites, regardless of their environmental characteristics. The strongest modification that follows boxelder invasion was the decline in U. dioica, the dominant species of the white willow forest understory. These differences were mainly correlated with a lower incident PAR under boxelder canopy. The greenhouse experiment identified PAR level as the main factor responsible for the changes in U. dioica stem number and biomass. Our results indicate that adult boxelder acts as an ecosystem engineer that decreases light availability. The opportunistic invasion by boxelder leads to important understory changes, which could alter riparian ecosystem functioning

Variabilite des peuplements riverains de l'Adour. Influence de la dynmaique fluviale a differentes echelles d'espace et de temps

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 83162 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

16. Ecosystèmes aux interfaces terre/eau

Aux interfaces terre-mer, comme aux franges des eaux continentales, s’établissent des écosystèmes animés de pulsions hydrologiques différenciées, déterminant des gradients spatiaux et temporels marqués. Les zones riveraines* des cours d’eau et les mangroves des littoraux tropicaux en sont deux exemples emblématiques, au sein desquels les crus et les courants, comme le balancement quotidien des marées, conduisent à des fonctionnements écologiques et à des patrons de biodiversité contrastés (cf..

La restauration de la continuité écologique de la Garonne est-elle favorable à la valorisation d'un patrimoine naturel ou culturel ? Le projet Réseau (ZA Pygar)

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