Root reinforcement and slope bioengineering stabilization by Spanish Broom (<i>Spartium junceum</i> L.)

Abstract

Abstract. The present paper deals with the root system's characteristics of Spanish Broom (Spartium junceum L.), a species whose capacity for adaptating and resisting to drought is worth investigating. In particular, the aims of the study were 1) to investigate the plant's bio-mechanical aspects and 2) to verify whether root reinforcement and the field rooting ability of stem cuttings enhance its potential for use in slope stabilization and soil bio-engineering techniques, particularly in the Mediterranean areas.Single root specimens were sampled and tested for tensile strength, obtaining classic tensile strength-diameter relationships. Analysis were performed on the root systems in order to assess root density distribution. The Root Area Ratio (RAR) was analyzed by taking both direct and indirect measurements, the latter relying on image processing. The data obtained were used to analyze the stability of an artificial slope (landfill) and the root reinforcement. The measurement and calculation of mean root number, mean root diameter, RAR, root cohesion and Factor of safety are presented in order to distinguish the effect of plant origin and propagation.Furthermore, tests were performed to assess the possibility of agamic propagation (survival rate of root-ball endowed plants, rooting from stem cuttings). These tests confirmed that agamic propagation is difficult, even though roots were produced from some buried stems, and for practical purposes it has been ruled out.Our results show that Spanish Broom has good biomechanical characteristics with regard to slope stabilization, even in critical pedoclimatic conditions and where inclinations are quite steep, and it is effective on soil depths up to about 50 cm, in agreement with other studies on MediterCorrespondence to: F. Preti (federico.preti@unifi.it) ranean species. It is effective in slope stabilization, but less suitable for soil bio-engineering or for triggering natural plant succession.

Method for synchronisation of soil and root behaviour for assessment of stability of vegetated slopes

“…The use of this model, subject of criticisms due to potential overestimation of root reinforcement (Preti and Giadrossich, 2009;, was justified by the comparable results of the measured vs calculated shear resistance of the soil rooted with vetiver roots (Mickovski and van Beek, 2009). …”

“…The development and use of plant root reinforcement models to assess the effects of vegetation in slope stability analysis has become a prominent research area all over the world in the last 10 years with research developments in root anchorage models (Pollen and Simon, 2005;Norris et al, 2008;Stokes et al, 2009;Preti and Giadrossich, 2009;Schwarz et al, 2010;Fan, 2012;Bourrier et al, 2013) and their application in practical stability problems such as shallow landslides or soil erosion (Coppin and Richards, 2007;Danjon et al, 2007;Schwarz et al, 2010;Comino and Druetta, 2009;Mickovski and van Beek, 2009;Thomas and Pollen-Bankhead, 2010).…”

Influence of the spatial layout of plant roots on slope stability

“…Wu et al (1979) and Waldron (1977) reported the effects of plant root on soil shear strength as attribute to increase of soil cohesion. Preti and Giadrossich (2009) fixed the coefficient of additional soil cohesion and reduced the overestimate effect of root architecture. The strength of plant roots is here substituted by soil cohesion.…”

“…The mechanical mechanisms (Greenway, 1987;Waldron, 1977;Ziemer, 1981) and hydrological mechanisms (Gyssels et al, 2005;Nilaweera and Nutalaya, 1999) of plant roots have been proved to promote soil shear strength, therefore protecting slopes from soil failure and shallow landslides. A reasonable collocation of plant and engineering measures can prevent water loss and soil erosion effectively (Coppin and Richards, 1990;Preti and Giadrossich, 2009;Reubens et al, 2007;Stokes et al, 2009;Thomas and Pollen, 2010). Plants are the main materials used in ecological engineering, as they can largely determine the quality of engineering projects.…”

Differential effects of two species of arbuscular mycorrhiza on the growth and water relations of Spartium junceum and Anthyllis cytisoides

“…At the end of the recovery period, water relation parameters in S. junceum were not significantly different among treatments. Both plants, indigenous legumes from semi arid Mediterranean shrub lands, are often used in revegetation strategies (Requena et al 2001;Preti and Giadrossich 2009). The use of mycorrhiza inoculated plants can enhance plant growth and also improve the response to drought, thus increasing the possibilities of survival and growth of these plants in an arid environment.…”