A review of the effects of throughfall and stemflow on soil properties and soil erosion

Abstract

Over a large fraction of the global landsurface, precipitation interacts with standing vegetation or organic litter prior to reaching the mineral soil. This interaction has both benefits and costs for plants, and these arise over varying timescales from minutes or hours to years or decades. A two-way interaction emerges in which the precipitation-vegetation interactions can affect plant growth, which in turn may alter the nature of the physical processes responsible for the plant-precipitation interactions via changes in plant architecture. This chapter explores two important examples of these processes. These are canopy changes in the drop size characteristics of water reaching the mineral soil, and the occurrence of contact flow or ‘stemflow’. Both may result in important hydrologic and erosional outcomes in forests, shrublands, and croplands, some of which are beneficial to plants, and some potentially detrimental. In particular, the effect of vegetation canopies in creating throughfall drops that are larger than those of open-field rainfall may result in higher sub-canopy erosivity. Likewise, the rainwater funnelling action of vegetation canopies and the resulting focussed delivery of stemflow may result in overland flow and scour of the soil surface around the base of some plants. Many of the interactions of precipitation and vegetation are conditioned by the characteristics of the open-field rainfall incident upon plant canopies; the chapter therefore also presents an overview of some of the key attributes of rainfall as they relate to processes acting on, within, and beneath vegetation. In many cases, the most important attributes of rainfall relate to the timescales characteristic of rainfall events, including event duration, depth, and intensity. These, and the nature of the vegetation and soils, exhibit wide geographical variability. This leaves many significant challenges facing the development of a full understanding of the interactions of rainfall, vegetation, and soils.