Land use, runoff, erosion and their control: a review for southern China

Abstract

Runoff and soil erosion, based upon plot studies, have been reviewed for southern China. They reveal, with the exception of tree crops, no strong association for a given land use between runoff and erosion. The data support the concept of vegetation as a major control upon runoff and sediment production. Forest and woodland have an average erosion rate of 0.05 t ha-1 year-1; the lowest rate for a given cover. Tree crops experience a slightly higher erosion rate followed by a scrub-grass cover. Cultivated slopes and bare soil, with respective mean erosion rates of 62.4 and 153.0 t ha-1 year-1, experience the greatest erosion. In terms of runoff production the ranking (low to high) goes from forest-woodland, scrub-grass to tree crops and bare to cultivated slopes. Sediment yield and runoff under various ground covers are presented as a ratio to those obtained under forest and this underlines the influence of land use. Further support is given by the use of additional studies from South-east Asia and Tanzania. Variability of sediment production, and to a lesser extent runoff under any given land use or cover, is an important feature of the data. Results from a study in Hong Kong support the importance of ground cover in controlling erosion. For example, sediment yield in splash pans on two plots where vegetation was cut were 2.6 and 3.8 times those of the control. Two plots, which were burnt, had sediment catches 5.4 and 3.1 times those of the control. However, observations of suspended sediment levels in a small stream suggest no great change in sediment levels after burning, which raises the question of sediment delivery from slopes to channels. The erosion rates reported for cultivation raise the question as to how long such rates can continue before productivity is affected. Further consideration needs to be given to economic aspects of erosion and to temporal variability.