| Changing hydrologic regimes and increasing erosion rates threaten many tropical upland ecosystems and have been attributed to conversion from tropical forest to agricultural use. A series of experiments were conducted in headwater catchments to quantify the effect of land uses common to the steep slopes and thin, calcareous soils on surface hydrology and soil movement.;To compare the surface hydrologic response of forested, tilled, swidden and pasture catchments, overland and subsurface runoff were collected separately for each land use. The forest site demonstrated the lowest runoff response and the highest rainfall threshold which initiated runoff. Conversely, the pasture sites demonstrated the greatest runoff response with the lowest rainfall thresholds which initiated runoff. The plowed and slash/mulch sites produced similar relationships between rainfall and total runoff, 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 swidden and forest sites.;The Alkalinity saturation ratios of interflow samples and the runoff responses were compared between sites, with the results supporting the hypothesis that disturbance of the soil surface results in progressive plugging of the epikarst by soil particles transported along macropores. The resultant throttle to percolation is evidently the greatest for fields under cultivation and may decrease after the cessation of tillage.;The transect cable technique was developed as a simple and robust method for measurement of soil loss and redistribution on steep slopes. Soil erosion rates from tilled sites, both with and without farmer-adapted contour-hedgerows, a no-till swidden and two pastures were assessed by measurement of the change in soil surface height along representative transects at each site. The most effective controls on erosion were found to be reduced tillage and soil surface management. Little erosion was measured at either the untilled slash/mulch site or the overgrazed pasture fallow. For the tilled sites, establishment of vegetative cover following tillage was found to reduce water-borne erosion whereas tillage erosion was found to increase with both frequency of tillage operations and installation of contour-hedgerows. |
