The influence of herbaceous vegetation on slope stability - A review

Worldwide, shallow slope failure is a problem causing environmental and economic damage. Vegetation plays an important role for the stabilization of slopes. Accordingly, ecological slope engineering aims at improving the stabilizing effect of vegetation by combining knowledge of ecology and engineering. The majority of scientific studies and related methods have addressed slope stabilization mechanisms of woody vegetation. Herbaceous vegetation can also stabilize slopes, yet, follows only partly the same mechanical and ecological principles. This imbalance of knowledge leads to the broad perception that woody vegetation is generally better for slope stabilization than herbaceous vegetation. In this literature review, we critically discuss the slope stabilization potential of herbaceous vegetation as compared to woody vegetation and summarize the state-of-the-art knowledge on slope stabilization with herbaceous vegetation. We found that performance of both woody and herbaceous vegetation is highly variable and depends on specific local growth conditions, location-specific requirements, species composition, and plant health. Depending on the specific context, either herbaceous or woody vegetation can be more suitable for slope stabilization, or both can perform similarly. The review showed that slope stabilization concepts are developed insufficiently for herbaceous vegetation and thus future research should address the specific stabilization mechanisms, including vertical and horizontal root connections, as well as root distribution, geometry, and tensile strength. Herbaceous vegetation responds faster to environmental changes than woody vegetation. Therefore, it is important to integrate ecological processes related to herbaceous plants into research and planning approaches.