Reinforcement of soil by fibrous roots

The capacity of plant roots to mechanically reinforce soil is one of the key processes underlying soil sustainability. Two of the greatest soil disasters in recent history, the Great Dust Bowl in the Midwest of the USA and the rapid degradation of China’s Loess plateau, were due to the depletion of native plants with dense, fibrous, interconnecting networks of plant roots that bound soil. This chapter discusses research advances and challenges in understanding soil reinforcement by fibrous roots. It bridges concepts from soil science, plant biology, geography and geotechnical engineering. The applications of the research include soil sustainability, the restoration of severely degraded soils and the mechanical stabilization of engineered slopes. Most work on soil reinforcement by roots focuses on woody species, with much less research on herbaceous species such as grasses and major crops. Tree roots penetrate deep into soil, thereby potentially bridging and reinforcing shear zones that could cause shallow landslides. This has prompted research interest from geotechnical engineers who have developed numerical models to predict soil reinforcement by tree roots. Concepts from woody species are somewhat transferable to fibrous root systems, although rooting depth and the extent of soil aggregation are different. This chapter considers how the concepts and models can be transferred, including areas where understanding is currently poor.