The impact of large Trees on bedrock denudation on forested hillslopes in the southern United States

Trees can have bioprotective effects, such as binding soil on rocky surfaces. Trees are shown to have a predominantly bioerosive effect on exposed bedrock surfaces, however, through the development and growth of root grooves on siliceous sandstone; further, trees have opened joints and bedding planes, facilitating infill by root hairs and micro-organisms. Uprooted trees bring fresh, unweathered bedrock to the surface, attesting to the biomechanical weathering of subsoil bedrock, and extension of the root wad into bedrock. An extensive study of soil depths beneath, and adjacent to, dead trees demonstrates that trees significantly deepen soil in this environment; topographic variables are not closely related to soil thickness on the hillslopes. Since the publication of Yatsu's (1988) The Nature of Weathering, biomechanical and biochemical weathering processes have been investigated at a range of scales. This paper examines the impact of large trees on bedrock denudation on forested hillslopes in the southern United States, based on both fieldwork and a review of recently published studies.