Soil and water bioengineering: practice and research needs for reconciling natural hazard control and ecological restoration

Soil and water bioengineering is a technology that encourages scientists and practitioners to combine their knowledge and skills in the management of ecosystems with a common goal to maximize benefits to both man and the natural environment. It involves techniques that use plants as living building materials, for: (i) natural hazard control (e.g., soil erosion, torrential floods and landslides) and (ii) ecological restoration or nature-based re-introduction of species on degraded lands, river embankments, and disturbed environments. For a bioengineering project to be successful, engineers are required to highlight all the potential benefits and ecosystem services by documenting the technical, ecological, economic and social values. The novel approaches used by bioengineers raise questions for researchers and necessitate innovation from practitioners to design bioengineering concepts and techniques. Our objective in this paper, therefore, is to highlight the practice and research needs in soil and water bioengineering for reconciling natural hazard control and ecological restoration. Firstly, we review the definition and development of bioengineering technology, while stressing issues concerning the design, implementation, and monitoring of bioengineering actions. Secondly, we highlight the need to reconcile natural hazard control and ecological restoration by posing novel practice and research questions

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

Citation: Ruiz-Villanueva, V., Piégay, H., Gurnell, A. A., Marston, R. A., & Stoffel, M. (2016). Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges. Reviews of Geophysics. doi:10.1002/2015RG000514Large wood is an important physical component of woodland rivers and significantly influences river morphology. It is also a key component of stream ecosystems. However, large wood is also a source of risk for human activities as it may damage infrastructure, block river channels, and induce flooding. Therefore, the analysis and quantification of large wood and its mobility are crucial for understanding and managing wood in rivers. As the amount of large-wood-related studies by researchers, river managers, and stakeholders increases, documentation of commonly used and newly available techniques and their effectiveness has also become increasingly relevant as well. Important data and knowledge have been obtained from the application of very different approaches and have generated a significant body of valuable information representative of different environments. This review brings a comprehensive qualitative and quantitative summary of recent advances regarding the different processes involved in large wood dynamics in fluvial systems including wood budgeting and wood mechanics. First, some key definitions and concepts are introduced. Second, advances in quantifying large wood dynamics are reviewed; in particular, how measurements and modeling can be combined to integrate our understanding of how large wood moves through and is retained within river systems. Throughout, we present a quantitative and integrated meta-analysis compiled from different studies and geographical regions. Finally, we conclude by highlighting areas of particular research importance and their likely future trajectories, and we consider a particularly underresearched area so as to stress the future challenges for large wood research. ©2016. American Geophysical Union

Réponse de cinq espèces ligneuses à l'ensevelissement sous des sédiments marneux

National audienceIn marly lands of the French Southern Alps, harsh soil erosion results in sediment movements during intensive rainfall events. Plants can be submitted to sediment burial in their early stages of development and their protective function is reduced. In a context of land restoration, it is important to know species responses to environmental disturbances. However, few studies about woody species tolerance to burial by sediment have been carried out. Seedlings of five woody species were buried in marly sediment at three different depths in pot experiment during eight weeks: no burial (control), partial burial (50% stem height) and complete burial (100% stem height). Heights through time, biomass and survival rates were measured to assess species responses. Results show that plant resistance to burial varies between species and three different responses were identified: negative (Hippophae rhamnoides, Ononis fruticosa), neutral (Robinia pseudo acacia, Pinus nigra) and positive (Acer campestre

Responses of five woody species to burial by marly sediment: the role of biomass allocation pattern flexibility.

International audienceAims In eroded lands of the French Southern Alps , burial of early established seedlings under marly sediment weakens the effect of vegetation on soil stabilization and sediment trapping. Therefore , this protective role is largely dependent on species ' resistance to burial , and the understanding of species ' tolerance to this environmental disturbance is highly valuable for basic knowledge on plant succession and for ecological restoration purposes. Methods The response of five woody species with contrasting ecological requirements and natural habitats—three tree species , Pinus nigra , Robinia pseudoacacia and Acer campestre , and two shrubs , Ononis fruticosa and Hippophae rhamnoides—to experimental burial under marly sediment was studied. Seedlings were exposed to three burial levels : no burial (control) , partial burial (50% of seedling height) and complete burial (100% of seedling height). Burial tolerance was evaluated based on seedling survival , height and biomass. Biomass allocation to shoots and roots and soluble sugar and starch contents in roots and stems were measured to identify plant traits that determine species response to burial. Important Findings All species survived partial burial but only A. campestre seedlings emerged from complete burial. Tree species were more tolerant to burial and buried plants showed no significant differences with control . The two shrubs were found less tolerant and buried plants showed slower growth than controls. The results showed that species response was not related to initial soluble and starch content in roots and stems , but instead to biomass allocation pattern flexibility. Keywords : burial d sediment d marls d response to burial d plant trait

Plant functional traits and species ability for sediment retention during concentrated flow erosion

International audienceBackground and aims Plant species can have a major effect on erosion dynamics and soil losses by retaining sediment transported during concentrated runoff. Identifying plant functional traits that influence and predict a species ability for sediment trapping is therefore of great interest, especially to improve management and restoration of degraded lands. Methods Sediment trapping ability of four morphologically contrasted species, the broadleaf species Buxus sempervirens and Lavandula angustifolia, and the coniferous species Juniperus communis and Pinus nigra, were investigated with flume experiments. Six functional traits describing stem, leaf and the overall plant morphology, were measured on seedlings. Analyses were performed to compare species efficiency in sediment trapping and to identify traits related to the amount of sediment trapped. Results Sediment trapping (RTS) was the highest upslope of Lavandula and the lowest upslope of Juniperus. Principal component analysis showed that RTS was best correlated (positively) with canopy density, described by plant biomass and leaf area per unit volume of plant. Leaf area and plant roundness were also positively related to RTS but to a lesser extent. Conclusions The results of this experimental study suggest that canopy completeness, leaf morphology and plant shape influence sediment retention by plants. Such knowledge may improve the diagnosis of land vulnerability to erosion and the prediction of ecosystem functioning after ecological restoration by the construction of bioengineering works in gully floors

Traits racinaires des plantes agissant sur la résistance des sols à l'érosion concentrée

International audienceThe effect of plant species on erosion processes may be decisive for long-term soil protection in degraded ecosystems. The identification of functional effect traits that predict species ability for erosion control would be of great interest for ecological restoration purposes. Flume experiments were carried out to investigate the effect of the root systems of three species having contrasted ecological requirements from eroded marly lands of the French Southern Alps [i.e. Robinia pseudo acacia (tree), Pinus nigra austriaca (tree) and Achnatherum calamagrostis (grass)], on concentrated flow erosion rates. Ten functional traits, describing plant morphological and biomechanical features, were measured on each tested sample. Analyses were performed to identify traits that determine plant root effects on erosion control. Erosion rates were lowest for samples of Robinia pseudo acacia, intermediate in Achnatherum calamagrostis and highest in Pinus nigra austriaca. The three species also differed strongly in their traits. Principal components analysis showed that the erosion-reducing potential of plant species was negatively correlated to root diameter and positively correlated to the percentage of fine roots. The results highlighted the role of small flexible roots in root reinforcement processes, and suggested the importance of high root surface and higher tensile strength for soil stabilization. By combining flume experiment to plant functional traits measurements, we identified root system features influencing plant species performance for soil protection against concentrated flow erosion. Plant functional traits related to species efficiency for erosion control represent useful tools to improve the diagnosis of land vulnerability to erosion, plant community resistance and the prediction of ecosystem functioning after ecological restoration