Effects of Acacia auriculiformis and Acacia mangium Plantion on Soil Properties of the Forest Area Degraded by Forest Fire in Mt. Makiling, Philippines

The study was conducted in the Acacia plantation and grassland sites degraded by forest fire, located at Mt. Makiling, Philippines to compare their soil properties of Acacia plantation and grassland areas and to examine the effects of planted Acacia species on soil properties of degraded forests. Forest fires had occurred until 1993 by repeated slash-and-burn activities. The areas had been dominated by Imperata cylindrica, but Acacia auriculiformis and Acacia mangium were planted in 1993 and 1994 to preserve the watershed. The soil samples from each of the sites were collected using soil auger at depths of 0-15cm and 15-30cm below ground surface in July 2003, and analyzed for moisture content, bulk density, organic carbon, total nitrogen, pH, CEC, available phosphorus, dehydrogenase and phosphatase. Between Acacia plantation and grassland sites, there were no differences in organic matter content and CEC. However, total nitrogen contents and dehydrogenase activity were significantly higher in the Acacia plantation site whereas moisture content and C/N ratios in grassland site were rather higher than those of Acacia plantation site. Total nitrogen and available phosphorus in the Acacia mangium site were significantly higher than those of A. auriculiformis site, indicating that Acacia mangium is recommended for planting to improve soil of degraded lands by forest fire.