Effect of hill fire on upland soil in Hong Kong

The present study compares the soil chemical properties of a new burnt site and an old burnt site, which had experienced three and one fire(s) respectively since 1988. The new burnt site is presently reduced to grassland and the old burnt site to mixed grassland/scrubland. Repeated fires raised soil pH by 0.27-0.33 units, exchangeable H and K by over 100%, but reduced total exchangeable acidity by 85%, organic matter by 86%, total Kjeldahl nitrogen by 75%, NH4 by 44%, NO3 by 42%, total phosphorus by 66%, exchangeable Na by 42%, Ca by 83%, Mg by 41%, Mn by 14%, Fe by 12% and Zn by 4% of the new burnt sire against the old burnt site. Fire similarly reduced the effective cation exchange capacity (ECEC) and the base saturation by 85% and 90%, respectively. The occurrence of successive fires is therefore hazardous to the environment and in the absence of fire for 6 years the old burnt site has accumulated sufficient organic matter and nitrogen needed for the invasion of the more nutrient-demanding tree species. The selection of tree species and site preparation pertaining to enhancement planting of the fire-disturbed slopes to accelerate forest development are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.