Initial soil changes associated with afforestation withAcacia auriculiformisandPinus kesiyaon denuded Grasslands of the Pantabangan area, Central Luzon, the Philippines

Abstract

The influence of afforestation on the soil of grasslands denuded for a long period of time was studied in plantations of 5-year-old Acacia auriculiformis and 8-year-old Pinus kesiya in comparison with the soils of adjacent denuded grasslands in Central Luzon, the Philippines. Soils where Acacia and Pinus grew were Ferralic Cambisols derived from Quaternary sediment containing large amounts of ironstone nodules and Chromic Vertisols from Tertiary mudstone, respectively. Soil physical properties improved by afforestation included the bulk density and porosity, though the effect was limited to the thin (0-5 cm) superficial soil layer. Hydraulic conductivity of the surface soil increased in the Acacia plantation, while that of the Pinus plantation decreased slightly due to abundant mycelia. The values of several chemical parameters decreased with plantation establishment for the surface soils: pH values, carbon and nitrogen contents, CEC, and concentration of exchangeable cations, especially of Ca²⁺, were generally lower in the surface soils under tree growth than in the grasslands. The decrease of these values was assumed to be a transitory phenomenon occurring only during the early stage of tree growth in the plantations in areas with a pronounced dry season. Available nitrogen content and its proportion to total nitrogen content in the top soil increased significantly by plantation establishment.