Runoff response and sediment yield of a landslide-affected fire-climax grassland micro-catchment (Leyte, the Philippines) before and after passage of typhoon Haiyan

Water budget and run‐off response of a tropical multispecies “reforest” and effects of typhoon disturbance

“…For this particular period, data from the uninterrupted record of the relatively sheltered lower rain gauge at the nearby Basper grassland (cf. J. Zhang, van Meerveld, et al, ) were used in regression equations linking the Basper gauge to the respective gauges at Manobo ( R 2 = 0.85–0.88) to estimate P at Manobo. No corrections were made for wind‐related underestimation of P because wind speeds (as measured at the Basper weather station) were generally low and the application of correction methods (e.g., Førland et al, ) for the extreme wind speeds encountered during the Haiyan event (Rabonza et al, ) would have led to unverifiable and uncertain corrections.…”

“…To explore the possibility of a positive trade‐off between the changes in infiltration and vegetation water use incurred by reforesting Imperata grassland in north‐eastern Leyte (as implied by the local claim of improved streamflow regime), comparisons were made between annual stormflow totals and annual apparent evapotranspiration (ET) for the Manobo reforest and the nearby Basper grassland studied by J. Zhang, van Meerveld, et al (). In doing so, it was assumed that the difference in quickflow production between the two catchments primarily represented the difference in rainfall infiltration and retention caused by the reforestation (cf.…”

“…These grasslands are found across the tropics in regions that experienced increasingly intensive slash‐and‐burn agriculture over the years (Brady, ) and are often dominated by spear grass ( Imperata cylindrica ) and wild sugar cane ( Saccharum spontaneum ; Garrity et al, ; Hooper, Legendre, & Condit, ; Styger, Rakotondramasy, Pfeffer, Fernandes, & Bates, ). Where regularly burned and grazed, they are typically associated with high storm run‐off (quickflow) and surface erosion (Chandler & Walter, ; Concepcion & Samar, ; J. Zhang, van Meerveld, Tripoli, Bruijnzeel, ). Therefore, fire‐climax grasslands are often targeted for reforestation (e.g., Ancog, Florece, & Nicopior, ; Otsamo, ; Wishnie et al, ) and—in areas with high land pressure—conversion to agroforestry systems (Murniati, ; Snelder & Lasco, ; Van Noordwijk, Hairiah, Partoharjono, Labios, & Garrity, ).…”

“…Specifically, we aimed to quantify the streamflow response to rainfall and the water budget of the 23‐year‐old reforest. Comparative observations were made in an Imperata grassland microcatchment at the nearby village of Basper (3.5 km from Manobo; J. Zhang, van Meerveld, et al, ) to serve as a baseline and to allow a preliminary test of the infiltration‐trade‐off hypothesis.…”

“…Due to continued oceanic warming, tropical cyclones are expected to become more forceful in the future (Balaguru, Foltz, Leung, & Emanuel, ), and heavy rainfalls in East and South‐east Asia appear to be on the increase as well (Chiang & Chang, ; Walsh et al, ), lending added importance to the study of the hydrological impacts of ecosystem disturbance by extreme events (Jayakaran et al, ; Lin et al, ; Scatena, Planos‐Gutierrez, & Schellekens, ). J. Zhang, Bruijnzeel, Quiñones, et al () reported very low (near‐) surface soil hydraulic conductivities in the Basper grassland, but much higher values for the Manobo reforest, whereas J. Zhang, van Meerveld, et al () showed the landslide‐infested grassland to be extremely responsive to rainfall and to generate large amounts of sediment. Production of both quickflow and sediment typically increases after tropical forest clearance (Bruijnzeel, ; Grip et al, ; Valentin, Agus, Alamban, Boosaner, & Bricquet, ) or disturbance during typhoon passage (J. D. Cheng, Lin, & Lu, ; Scatena et al, ), whereas the reverse applies after reforestation (Krishnaswamy et al, ; Scott et al, ; Sidle et al, ; Zhou et al, ).…”