Bioengineering techniques have been encouraged over “hard” civil engineering such as riprap for recovering naturalness on stabilized riverbanks, but their effectiveness in reproducing the plant ...species diversity and vegetation succession present on non-stabilized (natural) riverbanks has rarely been assessed. Here, we compared alpha and beta diversity and successional trajectories of plant communities along the vertical profile of natural (40 sites), bioengineered (51) and riprap (33) riverbanks, in 55 streams of the second- to seventh-order in the province of Quebec (eastern Canada). Richness of total, hydrochorous and native species was higher on natural riverbanks than on those stabilized by riprap techniques along all riverbank elevations (upper, middle and lower parts of the riverbank). Bioengineered sites showed intermediate values. Natural sites contributed most to beta diversity on the upper bank, riprap sites on the middle bank. Temporal changes in species richness were observed only on the upper and middle banks, with an increase on riprap sites and a decrease on bioengineered sites. Beta diversity was mainly stable through time. Plant composition on bioengineered sites converged to that on natural sites for all bioengineering techniques at all bank levels, whereas for ripraps it did so only on the lower bank. For all bioengineering techniques, plant succession was driven by increasing native and hydrochorous species at all bank levels. Bioengineering is an effective alternative to riprap on stabilized riverbanks that leads to plant diversity and succession that most resemble those on natural riverbanks.
•Bioengineering fosters alpha, but not beta plant diversity in riverbanks.•Species richness decreases from natural to bioengineered to riprap sites.•Vegetation on bioengineered sites converges to natural sites over time.•Bioengineering fosters native and hydrochorous plants along successional trajectories.•Vegetation differs along the vertical topographic gradient of stabilized sites.
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.
•Ice-related stresses in cold climates, such as mechanical breakups, complicate SWBE.•Biogeomorphology is key to enhancing SWBE strategies via better river understanding.•Understanding interactions between vegetation and ice could enhance SWBE techniques.•Understanding vegetation-river feedback dynamics is a decision-making tool for SWBE.•Biogeomorphic monitoring could refine SWBE techniques and identify maintenance needs.
Abstract
In riverine ecosystems, human‐induced stressors related to flow regulation and bank stabilisation have accumulated over time. The restoration of these highly anthropised ecosystems has ...become a major issue over the last few decades, with ambitious stated objectives. However, while the individual impact of flow regulation and channelisation on river functioning has been extensively studied, the response of ecological communities to multiple co‐occurring human‐induced stressors remains largely unexplored.
Using a sampling design based on five river reaches in the Rhône catchment, ranging from unregulated in flow and bedload transport to intensively regulated reaches, we sought to understand how the accumulation of anthropogenic stressors influenced the functional response of riparian plants communities on gravel bars. By using 12 ecological and morphological traits, we performed a classification analysis to construct six riparian guilds and investigated whether their representativeness, as well as the mean value of individual traits, varied with increasing levels of anthropogenic stressors.
Species cover and redundancy in several guilds increased or decreased significantly with increasing pressures. Thus, the guild of small taproot herbs with low nutrient and soil moisture requirements (xero‐oligotro‐taproot species guild) and the guild of taproot herbs adapted to very bright and dry conditions (mesoxero‐mesotro‐taproot species guild) dominated the unregulated reaches with active bedload transport. Conversely, regulated reaches with stabilised baseflow and inactive transport were dominated by the guild of flood‐tolerant trees (hygro‐perennial tall species guild) and the guild of vegetatively reproducing and flood‐tolerant perennial herbs (hygro‐perennial clonal species guild).
Analysis of individual traits revealed a shift in environmental conditions, from full light to shade tolerance and from dry to humid, with increasing anthropogenic stressors. In response to this decrease in drought levels, plants traits shifted from annual to perennial species, from sexual to vegetative strategies and from taproots to a fibrous root system.
Our results highlight the accumulated effects that anthropogenic stressors can have on riparian communities, inducing a progressive shift in certain traits related to life history, reproductive strategies, and drought adaptations. This effect on a set of shared traits reveals the strong influence that human infrastructures can have on the ecological niche of species and the morphological adaptations of riparian vegetation.
From an applied point of view, and for highly anthropised rivers, our results suggest that restoration actions targeting a single stressor will not be sufficient to reorient riparian plant communities towards an ecological state closer to reference systems. Since human‐induced stressors have often deeply altered the flow and sediment regimes of rivers, a more integrated approach based on the restoration of erosion and flooding processes is essential to allow the expression of a wider diversity of riparian plant communities and habitats.
Soil and water bioengineering techniques are now increasingly adopted worldwide for controlling riverbank erosion but have not yet been implemented in the Caribbean Islands biodiversity hotspot. The ...selection of suitable native plant species is critical for successful soil bioengineering designs on riverbanks, but few data are available regarding Caribbean species. This study aimed to characterize the performance and biotechnical traits of native Caribbean species potentially compatible with soil and water bioengineering. In a six-month shadehouse experiment, we measured the survival rate, biomass production and root growth of cuttings of ten native Caribbean shrub and tree species occurring naturally in a variety of riparian environments. All species appeared suitable for soil and water bioengineering but differed as to the specific bioengineering techniques they seemed particularly suited for, depending on their respective survival rates, growth performances and root system structures. Five tree species, Citharexylum spinosum, Cedrela odorata, Ficus citrifolia, Chimarrhis cymosa, Homalium racemosum, and three shrubs, Piper dussii, Piper dilatatum and Phyllanthus mimosoides, exhibited survival, growth and root characteristics compatible with a broad range of techniques, whereas Tabebuia heterophylla and Cordia sulcata may only be compatible with a few. We also propose using of the DEXi decision-support software for assessing species suitability to a series of widespread soil and water bioengineering techniques. Our results provide practical guidance for the integration of native species in soil and water bioengineering in the Caribbean and the Neotropics at large.
•Caribbean riparian trees and shrubs are promising for soil bioengineering.•A new approach is proposed to assess species suitability to the main soil bioengineering techniques.•Among the ten species tested, eight possess characteristics that make them suitable for soil bioengineering techniques.•These results will greatly facilitate the development of soil bioengineering in the Caribbean.
Nature-based Solutions (NbS) are promoted as practical and theoretical solutions that simultaneously provide human well-being and biodiversity benefits. One example is soil bioengineering using ...construction techniques based on living vegetation, and is frequently used for riverbank stabilization, flood protection, and erosion control. Compared with civil engineering, NbS offer many advantages such as cost reduction, limited impact on the environment, and production of ecosystem services. However, their use is still marginal for riverbank control, especially in urban areas. In this paper, we focus on soil bioengineering techniques for riverbank protection in an urban context from the practitioners’ perspective. We question to what extent NbS require a shift in management paradigm. We used qualitative methods to interview 17 practitioners working in the Rhone Alps basin (France). Our results reveal that switching from civil engineering to soil bioengineering is not only a technical change, but also requires a shift from a “predict and control” paradigm to an “adaptive management” paradigm because of three major reasons. First, soil bioengineering techniques require redefinition of the performance of engineering structures with the inclusion of ecological and social dimensions. Second, the adoption of soil bioengineering techniques requires that practitioners, elected people and inhabitants reconsider risk sharing and acceptance. Third, the techniques require practitioners to adopt a new posture, with new soft skills (humility and daring) and a new collective organization (collective feedback). Finally, we identify three levers for a broader use of such techniques: (i) systematic assessment of the ecological, economical, and social benefits of such techniques; (ii) improving risk acceptance and sharing; (iii) fostering of social learning among practitioners through collective or technical feedback.
•Adopting soil bioengineering techniques requires a management paradigm shift.•Shift is from the “predict and control” to the “adaptive management” paradigm.•Shift questions the performance definition, risk-taking and professional posture.•Three levers are identified for a broader use of such techniques.•Systematic assessment, broader risk acceptance and social learning are needed.
