Soil recovery from human disturbance in tropical woodlands in Hong Kong

Abstract

Villages in the countryside hinterland of Hong Kong traditionally preserve small remnant woodlands for utilitarian and spiritual reasons. In the territory, these remnants often furnish the most natural ecosystems with rich biodiversity. Some sites have been preserved, whereas others have been subject to different uses, and subsequently secondary woodland has reestablished. This study evaluates woodland and human influences on soil properties, and soil recovery after woodland rejuvenation. At nine sites, four classified as less disturbed (LD) and five as more disturbed (MD), physical and chemical properties are similar to those of impoverished humid-tropical soils. However, the MD samples have greater stone content and aggregate stability than the LD. MD samples also have higher pH, lower C/N ratios, more exchangeable Ca and Mg, and higher base saturation. The MD soil properties are attributed to tree felling in the 1940s and short-lived conversion to farmland or orchard, followed by secondary woodland succession dominated by native broadleaf trees. Two MD sites, one converted to an urban park in 1970 and the other burnt by a severe hill fire in 1999, have soil imprints of drastic disturbance. The nutrient content of MD soils at this early stage of ecosystem succession suggests rapid accumulation of nutrients. Five decades of secondary succession at three of the MD sites have resulted in natural soil rehabilitation. Conservation of these ecologically valuable woodlands should avoid unnecessary silvicultural inputs such as planting exotic species and soil disturbance, and conversion to unnatural uses such as recreational sites. In addition, the soils should be managed for improvement to help ecosystem recuperation. © 2002 Elsevier Science B.V. All rights reserved.