Morphological and Chemical Properties of Soils Along a Vegetation Gradient Affected by Fire in Hong Kong

This work examined the effects of hill fire on the morphology and soil chemical properties of a vegetation gradient that transcends a newly burnt short grassland, tall grassland, mixed grassland/shrubland, and woodland vegetation. Distinct soil horizons were observed, and the thickness of the O (1.5-6 cm) and A (4.5-21 cm) horizons decreased with successive development of the vegetation. Similarly, the immediate effect of fire on soil properties was observed, although it is difficult to discriminate between the effects of fire and those of vegetation. However, the effect on soil chemical properties seemed to dissipate with time after the fire and successional development. The fire effect raised pH, mineral nitrogen (NH+4 and NO−3), exchangeable Ca2+, and base saturation of the soils, but reduced soil organic matter (SOM) and total Kjeldahl nitrogen (TKN) and had no effect on total phosphorus, exchangeable K+, Na+, and Mg2+. Many of these effects disappeared 1 year after the occurrence of fire. In the absence of fire, natural succession proceeds in the sequence of grassland, mixed grassland/shrubland and woodland, each accompanied by specific changes in soil properties. The disturbed soils have obviously accumulated sufficient nutrients to support development of the woodland six years after the occurrence of fire.