Effects of land use change on soil characteristics and hydrology of experimental watersheds in Angat, Bulacan [Philippines].
1994
Dano A.M.
Burning of grassland watershed significantly increased available phosphorus and potassium content of the surface soil. Reforestation initially lowered P, K, Ca, Mg and CEC but litterfall accumulation improved the soil organic matter content and CEC after eight years. Annual summer burning of the grassland watershed decreased June to August streamflow compared to the protected grasssland watershed. This could be due to the higher evapotranspiration of the regrowth of the vegetation in the burned area. However, the protected grassland watershed had a lower sediment yield than the annually burned watershed by 25 percent. Three years after reforestation of the grassland watershed with Gmelina arborea annual streamflow started to decrease. The decrease in mean annual streamflow was about 186 mm. The decrease in annual streamflow is attributed to increase in consumptive use and interception loss of trees as they mature. However, annual baseflow increased by 16 mm. while annual direct runoff decreased by 155 mm. Reforestation reduced annual sediment yield by 52 percent compared to that of the annually burned watershed. Timber stand improvement and planting of agroforestry crops in a secondary dipterocarp forest watershed significantly increased sediment yield from 8 to ten tons/ha/yr. but had no significant effect on annual and monthly streamflow. The secondary dipterocarp forest watershed had better temporal distribution of monthly streamflow than the grassland covered watershed. The Univerity of Connecticuts' hydrologic model effectively simulated the monthly streamflow with the change in land use from grassland to reforestation with Gmelina arborea.
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