Ecological Engineering 95 (2016) 622–634 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Influence of forest stands and root morphologies on hillslope stability André Guy Tranquille Temgoua a,∗ , Nomessi K. Kokutse b , Zanin Kavazovi ´ c c a University of Ottawa, 120 University, K1N 6N5, Department of Earth Sciences, Ottawa, ON, Canada b PROCENVI Inc., 939 Rue Chapman, G2E 3Z4, L’Ancienne-Lorette, QC, Canada c Khalifa University of Science, Technology and Research, Abu Dhabi, UAE, Department of Applied Mathematics and Sciences, UAE a r t i c l e i n f o Article history: Received 3 January 2016 Received in revised form 4 June 2016 Accepted 18 June 2016 Keywords: Landslides Hillslope stability Root morphology 3D finite elements modelling Ecological engineering a b s t r a c t Forest plantations can help to reinforce soil and improve hillslope’s stability against shallow landslides. Based on 3D finite element method implemented in SIMULIA software, this paper develops a 3D numerical simulation model to assess impact of forest’s stands structure and 3D root system morphologies on hillslope’s stability. A preliminary analysis is performed to assess the impact of different stand parameters and root morphologies on the slope’s safety factor as well as on the volume of soil mobilized by a landslide. Regarding tree’s root morphology, we found that the overall slope’s stability mainly depends on the depth of root’s system and on additional cohesion provided by the roots. Hence, tap-like block morphology provides the best overall stability improvement. Furthermore, among the stand parameters, inter-tree distance in the slope direction has the greatest influence on the slope’s safety factor. The rectangular pattern of stand distribution exhibits the lowest inter-tree distance in the slope direction and significantly improves slope’s stability. Finally, the volume of soil mobilized during a landslide shows noticeable variations through root block morphologies. However, for a given root morphology, the stand distribution does not cause significant differences in the volume of soil mobilized during a landslide. © 2016 Elsevier B.V. All rights reserved. 1. Introduction In several mountainous regions around the world, mechanical instability of deforested slopes and landscapes is an increasing con- cern that requires a particular attention. Ecological restoration or suitable management practices of existing forest plantations can contribute to reinforce slopes and prevent shallow landslides (Sidle et al., 1985; Sakal and Sidle, 2004; Genet et al., 2010; Ghestem et al., 2013; Bischetti et al., 2015; Kokutse et al., 2015). In a wide range of situations, ecological engineering techniques for slope restora- tion against erosion and landslides are ecologically viable methods in the long term (Stokes et al., 2004; Norris et al., 2008; Zhou et al., 2015). Vegetation has been recognised to play a major role in the reinforcement of slopes against shallow landslides. The par- ticular stabilizing effect of tree roots is supported by numerous studies based on landslides inventories. These studies reveal an increase in landslide frequencies during the first years following timber harvesting (Bishop and Stevens, 1964; Gray and Megahan, 1981; Kuruppuarachchi and Wyrwoll, 1992). Results obtained by numerical modelling (Wu et al., 1988a; Wu et al., 1988b; Sidle and ∗ Corresponding author. E-mail address: atemgoua@uottawa.ca (A.G.T. Temgoua). Terry, 1992; Wu and Watson, 1998; van Beek et al., 2005; Kokutse et al., 2006; Genet et al., 2010; Lin et al., 2010; Ji et al., 2012; Mao et al., 2012; Schwarz et al., 2012a; Fan and Lai, 2013; Mao et al., 2013; Wu, 2013) unveil the same issue as well as observations made by analysing field data (Burroughs and Thomas, 1977; Wu et al., 1979; Terwillinger and Waldron, 1991; Riestenberg, 1994; Genet et al., 2008). Increasing efforts are being made in attempts to better understand how forest plantations and management could improve slope stability (Tsukamoto, 1987; Operstein and Frydman, 2000; Mao et al., 2013). It was also demonstrated that both tree’s roots and the diversity of forest species contribute to slope stabil- ity. Roots indirectly increase the soil shear strength through water extraction by transpiration (Waldron, 1977; De Baets et al., 2007). The intensity of root reinforcement mainly depends on roots distri- bution and root tensile strength (Bischetti et al., 2005; Pollen and Simon, 2005; Genet et al., 2008; Kuriakose et al., 2008; Ji et al., 2012; Schwarz et al., 2012b; Naghdi et al., 2013; Schwarz et al., 2013; Leung et al, 2014; Hwang et al., 2015; Schwarz et al., 2015). Although numerous experimental studies and field investiga- tions have confirmed that vegetation growing on a slope increases its stability, little consideration has been given to define the best strategies of forest management with regards to the risk of soil failure. Mixed forest plantations and natural forests exhibit spatial and temporal variability in species composition, tree distribution http://dx.doi.org/10.1016/j.ecoleng.2016.06.073 0925-8574/© 2016 Elsevier B.V. All rights reserved.