Freddy Rey

Ecological mitigation of hillslope instability: ten key issues facing researchers and practitioners

BackgroundPlants alter their environment in a number of ways. With correct management, plant communities can positively impact soil degradation processes such as surface erosion and shallow landslides. However, there are major gaps in our understanding of physical and ecological processes on hillslopes, and the application of research to restoration and engineering projects.ScopeTo identify the key issues of concern to researchers and practitioners involved in designing and implementing projects to mitigate hillslope instability, we organized a discussion during the Third International Conference on Soil Bio- and Eco-Engineering: The Use of Vegetation to Improve Slope Stability, Vancouver, Canada, July 2012. The facilitators asked delegates to answer three questions: (i) what do practitioners need from science? (ii) what are some of the key knowledge gaps? (iii) what ideas do you have for future collaborative research projects between practitioners and researchers? From this discussion, ten key issues were identified, considered as the kernel of future studies concerning the impact of vegetation on slope stability and erosion processes. Each issue is described and a discussion at the end of this paper addresses how we can augment the use of ecological engineering techniques for mitigating slope instability.ConclusionsWe show that through fundamental and applied research in related fields (e.g., soil formation and biogeochemistry, hydrology and microbial ecology), reliable data can be obtained for use by practitioners seeking adapted solutions for a given site. Through fieldwork, accessible databases, modelling and collaborative projects, awareness and acceptance of the use of plant material in slope restoration projects should increase significantly, particularly in the civil and geotechnical communities.

Linking plant morphological traits to uprooting resistance in eroded marly lands (Southern Alps, France)

In marly catchments of the French Southern Alps, soils are subjected to harsh water erosion that can result in concentrated flows uprooting small plants. Evaluating and predicting plant resistance to uprooting from simple plant traits is therefore highly important so that the most efficient plant strategy for future restoration of eroded slopes can be defined. Twelve species growing on marly land were studied. For each species, in-situ lateral uprooting tests were conducted and morphological plant traits were measured on small plants at the early stages of their development. The results show that maximum uprooting force was most positively correlated with stem basal diameter. Resistance to uprooting depends on a combination of several traits. Tap root length, the proportion of fine lateral roots and root topology were the best predictors of anchorage strength.

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

Background and aimsPlant 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.MethodsSediment 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.ResultsSediment 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.ConclusionsThe 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.

Morphological diversity of plant barriers does not increase sediment retention in eroded marly gullies under ecological restoration

AimsSediment retention by plant barriers initiates common strategies to conserve soil fertility or restore degraded terrains, including gullied ones. Differences in species performance for sediment retention have been studied but little is known about plant performance in retention when upscaling to plurispecific barriers. We investigated the role of morphological diversity of plant barriers in sediment retention in the context of eroded marly gullies.MethodsFifteen plant barriers, composed of combinations of four morphologically contrasting species (grass, shrub, dwarf-shrub and juvenile tree) were tested for their sediment retention potential in an innovative life-size artificial concentrated runoff experiment. We studied the net effect of biodiversity and the role of morphological traits on sediment retention.ResultsWe found that grass barriers performed best to retain sediment and morphological diversity significantly impaired sediment retention. This negative effect may be due to runoff concentrating in the least flow-resistant areas (shrubs or trees), resulting in a localized increase in flow velocity and thus an overall decrease in sediment deposition.ConclusionTo initiate gully restoration by increasing sediment retention in their bed, morphologically homogeneous plant barriers should be favored. Plant diversity, useful for mid- and long-term restoration goals, should be considered later in the process.

Integrating ecological engineering and ecological intensification from management practices to ecosystem services into a generic framework: a review

There are many management approaches proposed to link practices and ecosystem services. Their common aim is to improve the levels of specific ecosystem services by driving key ecosystem functions. However, an operational common grid of analysis is needed. Among these approaches, scientists have recently put forward ecological engineering and ecological intensification which provide relevant examples for building and testing a common grid. Here, we propose to integrate ecological engineering and ecological intensification into a generic framework from management practices to ecosystem services. The novelty of this framework is to consider management practices as gradients of inputs to ecosystems. Specifically, management actions are defined according to the type and level of inputs, characterized along a gradient from endogenous to exogenous inputs, and from biological to artificial inputs. Our framework highlights the importance of the interactions between management practices and natural capital properties. These interactions determine the ecosystem functions that will sustain target ecosystem services. We then show how ecological engineering and ecological intensification can be distinguished and unified within our framework. To illustrate this, we use four ecological engineering and ecological intensification case studies representing different types and levels of inputs. Our proposed framework should thus help (1) researchers to make improved assessments of the links between practices, ecosystem structure and functions, and ultimately services, and to foster improved meta-, cost-benefit- and life-cycle analyses and evaluations of ecosystem management approaches; (2) project designers by improving the adequacy of their action to the specified target; and (3) managers to establish the specifications of the ecosystem management adapted to their objective.

Revegetation of steeplands in France and New Zealand: geomorphic and policy responses

BackgroundEfforts to address erosion and land degradation in steeplands of many countries have largely relied on revegetation. The policy responses to this issue are many and varied as have been their successes. Revegetation efforts tend to occur when it is realised that deforestation, mountain land erosion, and flooding of rivers are linked.MethodsUsing the Southern Prealps region in France and the East Coast North Island region of New Zealand as ‘study sites’, past and current revegetation efforts to address steepland degradation were compared.ResultsBoth areas have similarities in geology, geomorphology and types of erosion processes (shallow landsliding and gullying). Landscape responses to large-scale erosion and subsequent reforestation have been similar between France and New Zealand though major reforestation occurred in France more than a century before that in New Zealand. Attempts to control sediment production in headwater regions reinforces the view that conditions controlling the evolution of channel response (through time and space) to a change in sediment supply are complex. While there is a consistent sequence of responses in channels and on hillslopes to reforestation efforts and the direction of changes may be anticipated, the magnitude and timing of those responses are not.ConclusionThe key lesson for future management and policy development arising from these studies is that erosion-control efforts that are aimed at producing basin-scale impacts will require targeting of areas where the proposed land use change or intervention will have the most beneficial influence on reducing sediment supply to river channels.

Linkages between root traits, soil fungi and aggregate stability in tropical plant communities along a successional vegetation gradient

AimsDetermining which abiotic and biotic factors influence soil aggregate stability (MWD) in tropical climates is often confounded by soil type. We aimed to better understand the influence of soil physical and chemical components, vegetation and fungal abundance on MWD of a Ferralsol along a successional gradient of vegetation in New Caledonia.MethodsFive plant communities (sedge dominated, open sclerophyllous shrubland, Arillastrum forest, Nothofagus forest and mixed rainforest) were studied. For each community, MWD, soil texture, soil organic carbon (SOC), iron (Fe) and aluminium (Al) sesquioxides, root length density (RLD), specific root length (SRL), root mass density (RMD) and fungal abundance were measured. Generalized linear models were used to predict MWD from soil and plant trait data.ResultsThe best prediction of MWD combined abiotic and biotic factors. Along the gradient, Fe increased MWD, while root traits, fungal abundance and SOC modified MWD. From the sedge-dominated community to Arillastrum forest, RMD and SOC increased MWD, while between Nothofagus and mixed rainforest, it was likely that floristic composition and fungal communities influenced MWD.ConclusionsPlant community, the intrinsic nature of Ferralsol and fungal abundance all modified MWD. However, the specific effect of microbial communities should be addressed through a metagenomics approach to elucidate microbial interactions with plant communities.

The Potential of Permanent Gullies in Europe as Geomorphosites

Geotourism is a useful way to educate societies in the field of geomorphology and related natural hazards. Geosites, including geomorphosites, represent the basis for the development of this type of tourism. This study describes 12 representative gully regions within nine European countries. The characteristics of 42 permanent gullies, gully systems, and badland landscapes are presented. Based on scientific values of the sites, educational lessons to be learned were identified that are mainly related to (i) gullies as a geological window, (ii) present-day geomorphological processes and (iii) stages of historical gully erosion reflecting past human–environment interactions. To evaluate possible education activities, a geotouristic assessment of the studied gullies and badlands was made, based on scientific, educational, functional and touristic indicators. This assessment demonstrates a large difference between the selected gully and badland sites, particularly with regard to functional and tourist values. The geotouristic potential of gullies (badlands) is the highest in Italy and Spain and the lowest in Romania and Latvia. In some countries, permanent gullies are not regarded as geotouristic attractions at all, while in others, they constitute a significant element of their tourism development strategy. In our opinion, all activities must be part of a broader strategy for the development of geotourism in gully and badland regions, for example, gullies may be included as geosites within existing or planned geoparks.

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.

Effects of fungal decay on elasticity and damping of small-diameter silver fir logs assessed by the transverse vibration resonant method

A number of studies have shown the ability of the vibration resonant method (VRM) to measure the modulus of elasticity (MOE) and the damping ratio (