TY - JOUR
T1 - Reforesting severely degraded grassland in the Lesser Himalaya of Nepal
T2 - Effects on soil hydraulic conductivity and overland flow production
AU - Ghimire, Chandra Prasad
AU - Bonell, Mike
AU - Bruijnzeel, L. Adrian
AU - Coles, Neil A.
AU - Lubczynski, Maciek W.
PY - 2013/12
Y1 - 2013/12
N2 - Severely degraded hillslopes in the Lesser Himalaya challenge local communities as a result of the frequent occurrence of overland flow and erosion during the rainy season, and water shortages during the dry season. Reforestation is often perceived as an effective way of restoring pre-disturbance hydrological conditions but heavy usage of reforested land in the region has been shown to hamper full recovery of soil hydraulic properties. This paper investigates the effect of reforestation and forest usage on field-saturated soil hydraulic conductivities (Kfs) near Dhulikhel, Central Nepal, by comparing degraded pasture, a footpath within the pasture, a 25-year-old pine reforestation, and little disturbed natural forest. The hillslope hydrological implications of changes in Kfs with land-cover change were assessed via comparisons with measured rainfall intensities over different durations. High surface- and near-surface Kfs in natural forest (82–232?mm?h-1) rules out overland flow occurrence and favours vertical percolation. Conversely, corresponding Kfs for degraded pasture (18–39?mm?h-1) and foot path (12–26?mm?h-1) were conducive to overland flow generation during medium to high intensity storms and thus to local flash flooding. Pertinently, surface- and near-surface Kfs in the heavily used pine forest remained similar to those for degraded pasture. Estimated monsoonal overland flow totals for degraded pasture, pine forest and natural forest were 21.3%, 15.5% and 2.5% of incident rainfall, respectively, reflecting the relative ranking of surface Kfs. Along with high water use by the pines, this lack of recovery of soil hydraulic properties under pine reforestation is shown to be a critical factor in the regionally observed decline in baseflows following large-scale planting of pines and has important implications for regional forest management.
AB - Severely degraded hillslopes in the Lesser Himalaya challenge local communities as a result of the frequent occurrence of overland flow and erosion during the rainy season, and water shortages during the dry season. Reforestation is often perceived as an effective way of restoring pre-disturbance hydrological conditions but heavy usage of reforested land in the region has been shown to hamper full recovery of soil hydraulic properties. This paper investigates the effect of reforestation and forest usage on field-saturated soil hydraulic conductivities (Kfs) near Dhulikhel, Central Nepal, by comparing degraded pasture, a footpath within the pasture, a 25-year-old pine reforestation, and little disturbed natural forest. The hillslope hydrological implications of changes in Kfs with land-cover change were assessed via comparisons with measured rainfall intensities over different durations. High surface- and near-surface Kfs in natural forest (82–232?mm?h-1) rules out overland flow occurrence and favours vertical percolation. Conversely, corresponding Kfs for degraded pasture (18–39?mm?h-1) and foot path (12–26?mm?h-1) were conducive to overland flow generation during medium to high intensity storms and thus to local flash flooding. Pertinently, surface- and near-surface Kfs in the heavily used pine forest remained similar to those for degraded pasture. Estimated monsoonal overland flow totals for degraded pasture, pine forest and natural forest were 21.3%, 15.5% and 2.5% of incident rainfall, respectively, reflecting the relative ranking of surface Kfs. Along with high water use by the pines, this lack of recovery of soil hydraulic properties under pine reforestation is shown to be a critical factor in the regionally observed decline in baseflows following large-scale planting of pines and has important implications for regional forest management.
KW - Dry-season flows
KW - Soil degradation
KW - Runoff generation
KW - Infiltration
KW - Forest Hydrology
U2 - 10.1002/2013JF002888
DO - 10.1002/2013JF002888
M3 - Article
VL - 118
SP - 2528
EP - 2545
JO - Journal of Geophysical Research: Earth Surface
JF - Journal of Geophysical Research: Earth Surface
SN - 2169-9003
IS - 4
ER -