The role of various types of artificial forest in soil and water conservation in South China

Abstract

Forest plantations are replacing natural forests worldwide. This study reviewed primary research papers published in China from 1994 to 2004 on soil and water conservation capability of plantation forests in South China. The aim was to understand the potential impact of replacing or compensating natural forest loss by artificial plantations in the region. The three most common plantation forests in South China are monocultures of Masson Pine Pinus massoniana (Pinaceae), China Fir Cunninghamia lanceolata (Taxodiaceae) and the bamboo Phyllostachys heterocycla cv. Pubescens (Gramineae). Whilst the review showed that the soil erosion index of derelict land was some 4.5 to 58 times higher than that under vegetation (shrubland, plantation or natural forest), plantation forest cover on the landscape scale is a poor reflection of the extent of soil erosion control. For example, despite high forest cover in Hunan (51%) and Jiangxi (53%) Provinces, soil erosion in forests in these two provinces was comparable to or even higher than on farming terraces. This is attributable to the uniformity and smoothness of the forest ground substrates of monoculture plantations and the removal of the existing vegetation cover (grass and shrubs) prior to tree planting in China. In the extreme cases, sites were burnt deliberately prior to reforestation. Soil erosion in the first year after planting can reach 8,000 ton km-2 and soil erosion will require 3 to 5 years to slow down. Most studies showed that litter productivity, which contributes to a forest’s ability in soil amelioration, was also generally lower (6-75%) in China Fir, Masson Pine or bamboo plantations than in natural forest. The canopies of bamboo, pine or fir plantations have been found to intercept (25-40%) less rainfall than those of natural forest. In summary, polyculture plantations, whether native or exotic, are better in soil and water conservation in South China.