Estimation of root cohesion for desert shrub species in the Lower Colorado riparian ecosystem and its potential for streambank stabilization

Quantifying mechanical properties of native vegetation for streambank stability is a critical need of the Lower Colorado riparian revegetation effort. In the present study we estimated root cohesion for four representative native desert shrub species: Artiplex lentiformis (Torr.) S. Watson, Lycium andersonii A. Gray, Larrea tridentata (DC.) Coville, and Allenrolfea occidentalis (S. Watson) Kuntze to understand their suitability in streambank stabilization in the framework of a revegetation campaign. Field experiments were conducted to measure root length, root length density, root area ratio, and root tensile strength. Finally, the root cohesion values were assessed using a simple perpendicular model.Root area ratio estimates showed that on average plant roots occupy 0.46% of the area under the crown of the selected species. The root tensile strength (Tr) was greatest for L. tridentata (62.23 MPa) followed by L. andersonii (53.53 MPa), A. lentiformis (49.17 MPa), and A. occidentalis (35.03 MPa). The root cohesion values could be used to rank the species according to their potential for shallow bank slope stabilization in riparian ecosystems of a desert environment. The maximum root cohesion in the present study was estimated for A. lentiformis (97.6 kPa) followed by L. andersonii (89.3 kPa), L. tridentata (35.6 kPa), and A. occidentalis (34.8 kPa). Root cohesion values were also estimated using Fiber bundle model (FBM) and compared to the perpendicular root model of Wu et al. (1979). The comparative root cohesion values for root diameter (>0.5 mm) suggest that Wu's model estimates are greater than those of the FBM by a reduction factor ranges between 0.35 and 0.56 for our studied species.