ABSTRACT Aim To characterize plant species pools and functional diversity of three common linear habitats—riparian corridors, roadsides and field margins—and to evaluate their potential roles in regional biodiversity conservation, particularly regarding invasive and threatened species. Location Temperate landscapes in the United Kingdom, France and Spain. Methods We compiled vegetation surveys and distinguished species common to multiple habitats and those restricted to a single habitat. We then compared taxonomic and functional diversity (as measured by hypervolumes) across habitats based on traits related to disturbance tolerance, ecological strategy and dispersal. Results A quarter of the species pool was shared among the three habitats, and indicator‐species overlap was strongest between roadsides and field margins. Riparian corridors had the highest species richness, the greatest number of habitat specialists and the largest functional trait hypervolumes. Roadsides showed comparable richness but substantially lower functional diversity, whereas field margins supported the lowest richness. Although field margins had more disturbance‐adapted annuals, all habitats showed similar functional diversity in disturbance tolerance. In contrast, ecological strategies and resource requirements differed strongly, reflecting habitat‐specific filtering by hydrology, soil conditions and management regime. Invasive species were most frequent in riparian corridors and roadsides, tended to be large and suited to productive, disturbed environments, while threatened species were more habitat‐specific, generally small, sensitive to eutrophication and associated with frequently disturbed but nutrient‐poor sites. Main Conclusions Riparian corridors emerge as hotspots of both taxonomic and functional diversity, but also as key invasion hotspots, whereas roadsides and field margins support narrower ecological strategies. The co‐occurrence of invasive and threatened species in disturbed sites within linear habitats, combined with their contrasting trait syndromes (height and nitrophily), highlights the need for coordinated management at a broader scale. Protecting vulnerable flora while limiting the spread of invasive species will require controlling nutrient inputs at the catchment scale.

ABSTRACTQuestionLinear habitats are terrestrial and aquatic corridors that can be natural or anthropogenic. Here we asked: how does the intersection of two types of linear habitats (roads and rivers) affect plant species diversity, composition and ecological attributes?LocationSouthern France.MethodsWe studied road‐river intersections (bridges) to test how composition, alpha and beta diversity, and ecological preferences of species in both roadside and riverside plant communities responded to the influence of bridges. We also used spatial predictors (spatial eigenvector maps) to assess whether bridges influenced directional spatial processes (upstream‐downstream river axis) structuring community composition.ResultsWe showed that vegetation around bridges differed from that away from bridges in terms of species composition and ecological preferences, and reduced alpha and beta diversities. We also found a convergence of species' ecological preferences in plant communities of rivers and roads at bridges. The turnover component of species beta diversity was lower at bridges, presumably due to different disturbance regimes, leading to biotic homogenization. However, our results show that the impact of bridges on directional spatial processes affecting species composition was negligible.ConclusionThe strong effect of bridges as selecting forces of plant communities for both rivers and roads suggests bridges should not be overlooked. Our findings will help the development of more effective management of both types of linear habitats for the conservation of the plant species they host and the associated ecological functions and ecosystem services they provide.

Le projet ADOFLO s’est intéressé aux changements de diversité et de fonctionnalités des végétations aquatiques et riveraines le long du fleuve Adour de 1989 à 2019, en se focalisant sur l’empreinte potentielle des effets des changements globaux (dont climatiques). L’apparente stabilité du nombre total d’espèces cache en réalité des remplacements liés en grande partie au changement global. Ces mutations posent désormais la question de la survie de cet écosystème sur la base d’une nouvelle biodiversité.

The structure and function of riparian ecosystems generally result from feedbacks between plant dynamics and fluvial processes and landforms, i.e., river morphodynamics. Taxonomic approaches do not allow to directly identify and quantify the mechanisms involved in the interaction between plant communities and the geomorphological environment. Although riparian ecosystems show enormous taxonomic variations, comparable patterns of plant response traits evolving across different taxa may evolve in response to the exposure to similar hydrogeomorphological processes in relation to flow dynamics, sediment transport, and nutrient and water availability. Biogeomorphological functional classifications for plant responses to, and effects on, river morphodynamics at the levels of individual plants, populations, and communities have been proposed in the literature. They have served here as a basis for identifying and quantifying, within a here presented standardised functional trait framework, key plant response and effect traits that can help to explain feedbacks between plants and morphodynamics. In particular functional guilds and functional diversity metrics can be applied at the population and community levels for exploring feedbacks between vegetation and river morphodynamics worldwide. In this framework, the variability in plant effects across different environments and spatiotemporal scales, related to the biological characteristics of the plants (i.e., morphological reconfiguration of plants into the flow, seasonal phenology, phenotypic plasticity, and vegetation succession), can be explored. New opportunities including remote sensing and numerical modelling approaches, coupled with the inclusion of plant traits through our original framework, shall improve our understanding of feedbacks between vegetation and morphodynamics and contribute to an improved prediction of biogeomorphological river trajectories.

Invasive plants represent a significant global challenge as they compete with native plants for limited resources such as space, nutrients and pollinators. Here, we focused on four invasive species that are widely spread in the French Pyrenees, Buddleja davidii, Reynoutria japonica, Spiraea japonica and Impatiens glandulifera, and analyzed their visual advertisement signals with respect to those displayed by their surrounding native species using a perceptual approach based on the neural mechanisms of bee vision given that bees are regular pollinators of these plants. We collected 543 spectral reflections from the 4 invasive species, and 66 native species and estimated achromatic and chromatic similarities to the bee eye. R. japonica, S. japonica and B. davidii were inconspicuous against the foliage background and could be hardly discriminated in terms of color from their surrounding native plants. These characteristics promote generalization, potentially attracting pollinators foraging on similar native species. Two morphs of I. glandulifera were both highly salient in chromatic and achromatic terms and different from their surrounding native species. This distinctive identity facilitates detection and learning in association with rich nectar. While visual signals are not the only sensory cue accounting for invasive-plant success, our study reveals new elements for understanding biological invasion processes from the perspective of pollinator perceptual processes.

Riparian zones extend from the edges of water bodies to upland communities in areas influenced by fresh water. The high biodiversity of riparian areas is created and maintained by inherent nutrient, sediment and biogeochemical processes, variable energy-flow and disturbance regimes, complex habitat, herbivory and other biotic processes. Riparian zones intercept and retain nutrients from upland runoff, as well as intercept and retain nutrients from adjacent streams and floodplains. Effectiveness of riparian buffering depends on soil and vegetative characteristics, as well as on river-riparian connectivity. Riparian zones are energy sources for adjoining aquatic systems via plant litter and arthropods falling into streams. Under natural conditions, large animals significantly influence nutrient and energy flows by altering physical characteristics and by herbivory. Connectivity – both the timing and extent of flows as well as the movements of animals – is fundamental for maintaining biodiversity and ecological services. Riparian zones are among the most vulnerable ecosystems facing global environmental change. Hence, preserving their biodiversity and the associated services is urgent.

Rivers have an intricate relationship with the vegetation that colonizes them. Riparian plants, capable of thriving within river corridors, both respond to and influence geomorphology. Yet interactions between river morphodynamics and vegetation tend to be context specific, making it challenging to generalize findings between locations. The current comprehension of vegetation interaction with physical processes, and especially its effects on river morphodynamics, still lacks clarity. This article examines numerous sources of variation in plant responses to, and effects on, river morphodynamics. Vegetation influences on geomorphological parameters vary in terms of intensity and spatial extent along the gradient of river energy and according to the fluvial style. Whilst feedbacks between vegetation and river morphodynamics are readily discernible at a local scale, on larger spatial scales, it can remain difficult to precisely determine cause-and-effect relationships that link hydrogeomorphic and vegetation drivers and the outcomes of their feedbacks. This is especially problematic for those feedbacks that give rise to emergent system landscape behaviour in meandering and island braided rivers. By contrast, in certain river configurations, such as anabranching rivers, the imprint of vegetation on the riverscape can be clearly evident. The imprint of vegetation is also supported by evidence from the ancient alluvial record. Through this review, we highlight key perspectives from a wide range of modern and ancient rivers of varied configuration in order to inform future studies of vegetation responses to, and effects on, river morphodynamics.

chessboard aims to facilitate the creation of connectivity matrices for sampling networks designed as regular grids.It can handle directed (asymmetric) and undirected (symmetric) spatial (or non-spatial) network connections.chessboard offers various methods to detect neighbors, all based on the chess game, allowing the creation of complex connectivity scenarios.

Poplars establish on alluvial bars within sand and gravel-bed rivers. Alluvial bars also provide particularly suitable habitats for the proliferation of ants. We hypothesized that ants, by modifying substrate structure and resource availability in fluvial habitats, positively influence poplar growth during its establishment stage. We conducted a preliminary nine-month ex situ greenhouse experiment with one ant species (Lasius niger L.) and six different genotypes of poplar cuttings (Populus nigra L.), both collected on the Garonne River, SW France. Three main treatments: ‘P. nigra alone’, ‘P. nigra without ants and with ant food’ and ‘P. nigra with ants and ant food’ were applied. After one growing season, we tested differences in branching length and biomass of stems, roots and leaves. Certain genotypes showed significant differences in growth, but there were no significant differences in stem length, dry mass of stems and roots between the three treatments. The total biomass of poplars after the first growing season was positively affected by the initial size of the cuttings and was modulated by the genotype independently from the treatments. However, an increased poplar growth for the treatment without ants and with ant food was observed according to significant differences in dry weight of leaves and total biomass (i.e. dry mass of stems, roots and leaves) for the pooled genotypes across treatments. We discuss our results with the aim of serving as a reference for future in situ and ex situ experiments and field measurements exploring interactions between ants and poplars, specifically in riparian ecosystems.

River ecosystems are spatiotemporally and intimately tied to physicochemical and biological processes, driven by strong feedbacks between riparian vegetation dynamics and hydrogeomorphic processes and fluvial landforms. Climatic and hydrogeomorphic constraints to vegetation determine a naturally shifting habitat mosaic dynamism, fostering high habitat heterogeneity and biodiversity, and providing multiple ecosystem services to society. However, most European river systems have lost their inherent highly dynamic character after major human-induced impacts, such as river channelisation and altered flow and sediment regimes. In March 2019, the United Nations designated the period of 2021–2030 as the "Decade on Ecosystem Restoration", and river ecosystems will be a significant target. Consequently, river restoration practitioners will need robust decision-making tools to guide their deliberations and subsequent management actions. Recommendations are to avoid merely reproducing river features and instead restoring geomorphic, hydrological, and ecological processes, but river science has not fully understood yet how processes develop and interact following restoration interventions. Integrative modelling of feedback mechanisms between riparian vegetation dynamics and hydrogeomorphic processes is critical for making predictions that enable river managers to optimise the use of the natural self-regulation potential of riparian corridors whilst maximising human benefits. Today’s existing models, however, do not fully reflect the interactions between river hydraulics and vegetation succession. In particular, the role of vegetation needs to be included through its impact in modulating river landforms and their evolutionary trajectories. Here, we present the conceptual and methodological framework, preliminary results, and the perspectives of the NUMRIP project, funded by the French National Research Agency. Along the project, a numerical (cellular automata) model of fluvial landscape dynamics will be developed, integrating physical, biological, and human components. The project focuses on riparian vegetation, from individual plants to communities. It explicitly considers vegetation as a dynamic component of the system, both responding to and affecting hydrogeomorphic processes and fluvial landforms. Accordingly, NUMRIP builds upon the conceptual fluvial biogeomorphological succession model and recent advances in remote sensing techniques of plant-geomorphology interactions. The NUMRIP project will explicitly associate plant functional traits (e.g., physiological, morphological, and biomechanical characteristics) to hydrogeomorphic processes and fluvial landforms, using plant functional trait approaches, remote sensing- and numerical modelling techniques. The lower course of the Allier River (France) is used as a case study. It is one of the last remaining free meandering river segments in Europe, and thus, constitutes an opportunity to investigate riparian succession processes of a dynamic, temperate river system. Despite its natural character, it is also experimenting an increase of stability (i.e., a reduction in channel migration and progression/retrogression of vegetation patches), because of a concomitant decrease of high and moderate magnitude floods due to current global climate change. The model could be used as a research tool in river science as well as a decision support system for river managers. It will be able to predict potential future evolutionary trajectories of fluvial corridors, adjusting for example to a changing hydrological regime or river restoration works.

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 permutational 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.

Riverbank erosion is linked to increasing risks in piedmont areas due to urbanization and hydromorphological alterations of rivers. Changes in riparian vegetation and in sediment dynamics modify aquatic macroinvertebrate communities. In this context, riverbank stabilization is a major issue in the conservation of stream ecosystem functioning. In this study, we aimed at assessing the impacts of riverbank stabilization techniques on the taxonomic and functional properties of benthic macroinvertebrate communities living in alpine mountain streams. For this purpose, the effects of four riverbank stabilization techniques (riprap, mixed, cribwall, and fascine) on the taxonomic richness and biological traits involved in the main ecological processes were tested and compared with natural bank conditions. Overall, the macroinvertebrate richness was lower in stabilized banks than in natural conditions, and communities welcomed on natural banks were significantly different from those found on managed banks. The biological trait composition such as "maximum potential size," "life cycle duration," "reproduction," "feeding habits," and "trophic status" differed significantly among riverbanks, especially between natural banks and the riprap, mixed, and cribwall trio. In a context of macroinvertebrate biodiversity and functional restoration, we can advocate the fascine technique as the most suitable technique tested.

Within riparian corridors, Salicaceae trees and shrubs affect hydrogeomorphic processes and lead to the formation of wooded fluvial landforms. These trees form dense stands and enhance plant anchorage, as grouped plants are less prone to be uprooted than free-standing individuals. This also enhances their role as ecosystem engineers through the trapping of sediment, organic matter, and nutrients. The landform formation caused by these wooded biogeomorphic landforms probably represents a positive niche construction, which ultimately leads, through facilitative processes, to an improved capacity of the individual trees to survive, exploit resources, and reach sexual maturity in the interval between destructive floods. The facilitative effects of riparian vegetation are well established; however, the nature and intensity of biotic interactions among trees of the same species forming dense woody stands and constructing the niche remain unclear. Our hypothesis is that the niche construction process also comprises more direct intraspecific interactions, such as cooperation or altruism. Our aim in this paper is to propose an original theoretical framework for positive intraspecific interactions among riparian Salicaceae species operating from establishment to sexual maturity. Within this framework, we speculate that (i) positive intraspecific interactions among trees are maximized in dynamic river reaches; (ii) during establishment, intraspecific facilitation (or helping) occurs among trees and this leads to the maintenance of a dense stand that improves survival and growth because saplings protect each other from shear stress and scour; (iii) in addition to the improved capacity to trap mineral and organic matter, individuals that constitute the dense stand can cooperate to mutually support a mycorrhizal network that will connect plants, soil, and groundwater and influence nutrient transfer, cycling, and storage within the shared constructed niche; (iv) during post-establishment, roots form functional grafts between neighbouring trees to increase biomechanical and physiological anchorage as well as nutrient acquisition and exchange; and (v) these stands remain dense on alluvial bars until a threshold of landform construction and hydrogeomorphic disconnection is reached. At this last stage, intraspecific competition for resources (light and nutrients) increases, inducing a density reduction in the aerial stand (i.e., self-thinning), but root systems of altruistic individuals could remain functional via root grafting. Finally, we suggest new methodological perspectives for testing our hypotheses related to the occurrence of positive intraspecific interactions among Salicaceae trees in fluvial landform and niche construction through in situ and ex situ experiments.

The ZA PYGAR project aims at studying the spatial dynamics of socio-ecological systems (SES) in SouthWestern France, going from the Pyrenees mountains to the plains of the Garonne river basin. PYGAR tries to answer three main scientific questions: 1/ What are the respective contributions of climate change and local anthropogenic disturbances to ecosystem changes (biodiversity, bio-physical characteristics)? 2/ How human practices drive ecosystem services? 3/ What are the relationships between resources availability and their accessibility, and the historic and prehistoric human population structure? The main transversal question of PYGAR is the adaption and response time of the different SES to global changes. The SES are studied at different time scales from the last glacial maximum to the present-day. PYGAR clusters 17 Labs (40 full-time permanent staffs: 23 researchers/professors & 17 engineers/technicians) from Toulouse and Bordeaux, supported by the University of Toulouse and several French research organisms (CNRS, INRA, IRSTEA, IRD, CNES, BRGM, Meteo France). Socioeconomic partners (companies, farmer's associations…) and public services (Occitania Region, Water Agency…) are strongly interested in the project. PYGAR includes 4 territories (sites ateliers): the central Pyrenees mountain range, the Garonne River, the agricultural hills and valleys of the Gascogne region and the Viaur-Aveyron river basin. The theory of SES provides a valuable tool to set up an interdisciplinary approach to deal with the co-evolution and resilience of the social and ecological templates of the studied systems facing global changes (climate change and land cover).

Control of invasive species within ecosystems may induce secondary invasions of non-target invaders replacing the first alien. We used four plant species listed as noxious by local authorities in riparian systems to discern whether 1) the severity of these secondary invasions was related to the control method applied to the first alien; and 2) which species that were secondary invaders persisted over time. In a collaborative study by 16 research institutions, we monitored plant species composition following control of non-native Tamarix trees along southwestern U.S. rivers using defoliation by an introduced biocontrol beetle, and three physical removal methods: mechanical using saws, heavy machinery, and burning in 244 treated and 79 untreated sites across six U.S. states. Physical removal favored secondary invasions immediately after Tamarix removal (0–3yrs.), while in the biocontrol treatment, secondary invasions manifested later (>5yrs.). Within this general trend, the response of weeds to control was idiosyncratic; dependent on treatment type and invader. Two annual tumbleweeds that only reproduce by seed (Bassia scoparia and Salsola tragus) peaked immediately after physical Tamarix removal and persisted over time, even after herbicide application. Acroptilon repens, a perennial forb that vigorously reproduces by rhizomes, and Bromus tectorum, a very frequent annual grass before removal that only reproduces by seed, were most successful at biocontrol sites, and progressively spread as the canopy layer opened. These results demonstrate that strategies to control Tamarix affect secondary invasions differently among species and that time since disturbance is an important, generally overlooked, factor affecting response.

Restoring the flooding-related disturbance regime by removing and setting back flood defenses (channel widening) is the most efficient strategy for recovering riparian plant communities in floodplains formerly impacted by human activities such as agriculture, mining, and forestry. Removing flood defenses is generally not socially accepted, and alternative recovery strategies must be explored. We assessed vegetation establishment on 33 sites in the floodplains of the Middle Ebro River and three of its tributaries (NE Spain) where restoration approaches applied in the last 20 years include channel widening, floodplain excavation, and abandonment of agriculture, gravel extraction, and hybrid poplar plantations, with and without plantation of native species. Using analysis of similarity and ordinations, we found that channel widening led to plant communities closely resembling those found on natural gravel bars, including new recruits of keystone tree species. Excavation of the floodplain as the restoration approach resulted in pioneer, non-strictly riparian communities. Abandonment of agricultural land or clearing of poplar plantations resulted in alternative stable states predominating, regardless of time elapsed since restoration and whether poles of native species were planted. However, forest-like communities relatively similar to mature, natural riparian references were attainable when hybrid poplars were allowed to resprout after clear-cutting, or after the human activities were abandoned and trees were not cut. Combining channel widening and assisted revegetation where flood defenses cannot be altered may partially reproduce a mosaic of habitats typical of natural floodplains.

Abandoning hybrid poplar plantations may be an alternative strategy for enlarging natural riparian corridors along regulated rivers where forest regeneration no longer takes place. Despite the generally high local diversity of plants in poplar plantations, their capacity to converge towards riparian forests following abandonment remains largely untested and uncertain, because maintenance‐related disturbance of plantations favors ruderal, not strictly riparian specialists. We assessed the spontaneous recolonization of vegetation in abandoned hybrid poplar plantations following two management strategies: harvesting or simple abandonment of standing trees. The floristic composition in four chronosequences of 10 active (1–15 years), 17 harvested (1–15 years), and 10 abandoned (8–20 years) hybrid poplar plantations, as well as 10 riparian sites established at gravel bars that appeared following the cessation of in‐channel gravel mining (8–25 years) along the highly regulated Garonne River (SW France) was assessed in the framework of ecological disturbance theory. Both harvested and abandoned sites still resembled active plantations more than riparian forests. When poplar resprouting was low after harvesting, sites were dominated by light‐demanding, nitrophilous herbs, sub‐shrubs, and vines showing both competitive and ruderal traits, and vegetation composition remained stable over time. Abandoned and harvested sites with high poplar resprouting developed forest communities in which competitive species that tolerate and generate shade dominated, and tree species recruitment was higher. Riparian sites hosted the highest number of indicator species, mainly wetland and exotic. Simple passive restoration strategies like abandonment of plantations can help create valuable ecosystems, although ones that diverge from riparian forests colonizing new fluvial landforms.

We examined how restoration of riparian vegetation has been implemented and evaluated in the scientific literature during the past 25 years. A total of 169 papers were read systematically to extract information about the following: 1) restoration strategies applied, 2) scale of monitoring and use of reference sites, 3) metrics used for evaluation, and 4) drivers of success. Hydro-geomorphic approaches (e.g., dam operations, controlled floods, landform reconfiguration) were the most frequent, followed by active plant introduction, exotic species control, natural floodplain conversion and grazing and herbivory control. Our review revealed noteworthy limitations in the spatio-temporal approaches chosen for evaluation. Evaluations were mostly from one single project and frequently ignored the multi-dimensional nature of rivers: landscape spatial patterns were rarely assessed, and most projects were assessed locally (i.e., ≤meander scale). Monitoring rarely lasted for more than six years and the projects evaluated were usually not more than six years old. The impact of the restoration was most often (43%) assessed by tracking change over time rather than by comparing restored sites to unrestored and reference sites (12%), and few projects (30%) did both. Among the ways which restoration success was evaluated, vegetation structure (e.g., abundance, density, etc.) was assessed more often (152 papers) than vegetation processes (e.g., biomass accumulation, survival, etc.) (112 papers) and vegetation diversity (78 papers). Success was attributed to hydro-geomorphic factors in 63% of the projects. Future evaluations would benefit from incorporating emerging concepts in ecology such as functional traits to assess recovery of functionality, more rigorous experimental designs, enhanced comparisons among projects, longer term monitoring and reporting failure.