First Author: Murielle GHESTEM

Affiliation: AgroParisTech ENGREF, AMAP, TA A51/PS2, 34398 Montpellier cedex 5, France

Second Author: Alexia STOKES1, Nick ROWE2, CAO Kunfang3, MA Wenzhang3

Affiliations: 1INRA, AMAP, TA A51/PS2, 34398 Montpellier cedex 5, France
2CNRS, AMAP, TA A51/PS2, 34398 Montpellier cedex 5, France
3Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences. Menglun, Mengla, Yunnan 666303, China

Abstract:
This study aims to integrate biomechanical knowledge for the development of eco-engineering techniques (where eco-engineering has been defined as the long-term, ecological strategy to manage a site with regard to natural or man-made hazards). Eco-engineering is used with increasing frequency and success in mountainous regions, where degradation can be large-scale due to land use change or natural processes e.g. mountain orogenesis. Combining the effective management of vegetation, soil and landscape, the development of eco-engineering strategies requires a multidisciplinary approach, where the understanding of plant biomechanics can play a large role.

The main objective of this study is to determine the different biomechanical strategies of plants growing on degraded slopes along the Salween River, Yunnan, China. The Salween River valley is one of the world's richest areas in terms of plant biodiversity but slope degradation through recent road building is leading to massive soil runoff and shallow landslides. As a consequence, the Salween River, a UNESCO World Heritage Site, and the longest undammed river in Southeast Asia, is heavily polluted from sediment runoff.

To use vegetation to reinforce soil on steep slopes, it is necessary to understand how roots and soil interact to provide cohesion. Root mechanical properties and architecture are the main components governing cohesion. Therefore, we are currently investigating how root tensile strength changes within a given architecture for several herbaceous and shrubby species e.g. Artemisia codonocephala, Buddleja officinalis Maxim, Coriaria nepalensis Wall. and Phyllanthus emblica L. These species are natural at the study site and grow on soil which is either eroded or heavily perturbed. Not only do root systems play an important role in holding soil in place, but the aerial architecture of a plant can be just as vital. For example, one highly abundant pioneer species which grows on degraded soil in the area is Bauhinia lecomtei. This liana develops many, flexible interconnected stems that act as a natural netting to limit movement of topsoil and scree. We are therefore examining the mechanics of Bauhinia stems, in addition to the mechanics of herb and shrub root systems.

Our results will help determine which species are most effectively planted and where in relation to the degradation processes occurring on a slope. We aim at identifying strategies for the management of degradation hotspots (a source area of sediments which can lead to larger off-site degradation) by connecting them to biodiversity hotspots (a significant reservoir of different species). Understanding the mechanical properties, nutrient and water needs, life history and competitive strategies of each species investigated will permit us to choose the best mixtures for producing sustainable slopes over time and space.