ABSTRACT
Both Hong Kong and Guizhou lie in China’s southern erosion region (Wen, 1993). This region is characterized by steep slopes, mostly at moderate elevations, deeply-weathered soil parent materials, annual rainfall totals mainly in the range of 1100–2500 mm, and high rainfall intensities, especially in the coastal zone open to typhoons, during which 500–600 mm of rain in two or three days are not uncommon. The original forest has long ago been removed from the uplands, for timber and fuel, as well as by forms of shifting cultivation. To some degree, especially in Hong Kong, native forest has been replaced by planted forests of Acacia, Pinus, and Cunninghamia, with scrub, grass, and Dicranopteris fern forming widespread secondary formations, their status being maintained by more or less regular cutting and burning. Contrary to general opinion, it seems possible that surface erosion under such secondary vegetation communities is quite limited, provided that the cover is closed. Cultivation is of much greater erosional significance outside Hong Kong. In Guizhou Province, for instance, more than half of the cultivated land area is sloping, much of that fraction growing rice or maize in summer and wheat or broad beans in winter, sometimes on slopes as steep as 35°, a practice technically illegal but one imposed by poverty and a lack of feasible alternatives. Some 40% of the land area in the province is regarded as ‘eroded,’ a proportion that is steadily increasing. This contrasts with a mere 4%, 4400 ha, of eroded badland in Hong Kong, where some 67.5% of the land area is reasonably well protected by forest plantings, scrub, grassland, and Dicranopteris fern (Hong Kong, 1995). However, the work of Peart (1995, 1997) shows that small areas of bare land such as those resulting from roadworks and powerline corridors can greatly influence sediment concentrations in streams.
