Runoff responses among common land uses in the uplands of Matalom, Leyte, Philippines

Changing tropical hydrologic regimes have been attributed to conversion from tropical forest to agricultural use and are a threat to many tropical upland ecosystems. A series of experiments were conducted in headwater catchments of Matalom, Leyte, Philippines, to quantify the effect on the near-surface hydrology of land uses common to the steep slopes and thin, calcareous soils. Overland and subsurface runoff were collected to compare the surface hydrologic response of forested, tilled, slash/mulch, and pasture catchments. The forest site demonstrated the lowest annual runoff response, at less than 3% of rainfall, and the highest rainfall threshold which initiated runoff. Conversely, the pasture site demonstrated the greatest annual runoff response (76%) with the lowest thresholds. A pasture with contour-hedgerows demonstrated greater infiltration than the pasture without this conservation practice, generating runoff at 31% of annual rainfall. The plowed and slash/mulch sites had similar annual runoff responses, at 17% and 13% of rainfall, although the predominant flow pathway differed between these sites. Surface runoff accounted for the majority of runoff at the plowed and pasture-fallow sites; whereas, interflow provided the largest contribution to runoff at the slash/mulch and forest sites.