MARSCHNER REVIEW Desirable plant root traits for protecting natural and engineered slopes against landslides Alexia Stokes & Claire Atger & Anthony Glyn Bengough & Thierry Fourcaud & Roy C. Sidle Received: 26 February 2009 / Accepted: 26 August 2009 / Published online: 23 September 2009 # Springer Science + Business Media B.V. 2009 Abstract Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrange- ment of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference ‘Ground Bio- and Eco-engineering: The Use of Vegetation to Improve Slope Stability— ICGBE2’ held at Beijing, China, 14–18 July 2008. Several papers from this conference are published in this edition of Plant and Soil. Keywords Soil cohesion . Root architecture . Slope stability . Soil mass wasting . Suction What is a trait? A trait is defined as a distinct, quantitative property of organisms, usually measured at the individual level and used comparatively across species. A functional trait is one that strongly influences organismal performance (McGill et al. 2006). Plant quantitative traits are extremely important for understanding the Plant Soil (2009) 324:1–30 DOI 10.1007/s11104-009-0159-y Responsible Editor: Yongguan Zhu. A. Stokes (*) INRA, UMR AMAP, 34398 Montpellier Cedex 5, France e-mail: alexia.stokes@cirad.fr C. Atger Pousse Conseil, Domaine de Fitzgerald, Le Mas Rouge, Chemin du Mas Rouge, 34970 Lattes, France A. G. Bengough Scottish Crop Research Institute, Dundee DD2 5DA, UK T. Fourcaud CIRAD, UMR AMAP, 34398 Montpellier Cedex 5, France R. C. Sidle Appalachian State University, Department of Geology, P.O. Box 32067, Boone, NC 28608, USA