Abstract
Imperata grassland soils are widely perceived as having poor physical and chemical properties that render them unproductive and prone to erosion. They are therefore increasingly targeted for reforestation across the tropics. To better understand how reforestation and forest growth affect soil hydrological processes we compared the soil physical characteristics for an Imperata grassland and a 23-year-old ‘reforest’ on Leyte Island, the Philippines. Saturated hydraulic conductivity (K sat ) was determined in the field (Amoozemeter, 20–90 cm depth) and the laboratory (small-core permeametry). Core-based values of K sat were (much) lower than field-based values, suggesting macropores were not sampled adequately with the small cores. K sat decreased exponentially with depth in both land-cover types, with a median field-measured K sat of the grassland of 2.1 mm h −1 at the surface and 2.9 mm h −1 at 20–40 cm depth, declining to ≤1 mm h −1 below 60 cm. Corresponding values for the reforest were 59 (at 20 cm), 37 (at 40 cm) and 7.3 mm h −1 (at 60–100 cm depth). Reforest K sat -values down to 60 cm depth were significantly higher than corresponding values in the grassland, but the difference disappeared at 90 cm depth. Organic carbon content in the top 40 cm of soil was slightly higher in the reforest than the grassland. Bulk density was higher and porosity marginally lower in the grassland than the reforest at all depths considered. The median five-min rainfall intensity (June 2013–May 2014) was 3.2 mm h −1 , suggesting that >50% of the rainfall might generate Hortonian overland flow in the grassland. Overland flow is unlikely in the reforest where lateral flow is likely to be generated around 60 cm depth for ~30% of rain-time, versus 2–3% between 20 and 60 cm. Within the limitations of the space-for-time substitution approach, these results suggest that 23 years of forest development at Manobo had a positive effect on hillslope hydrological functioning.
| Original language | English |
|---|---|
| Pages (from-to) | 163-177 |
| Number of pages | 15 |
| Journal | Geoderma |
| Volume | 333 |
| Early online date | 25 Jul 2018 |
| DOIs | |
| Publication status | Published - 1 Jan 2019 |
Funding
Financial support from the China Scholarship Council , VU University Amsterdam and the Australian Council for International Agricultural Research (ACIAR Grant no. ASEM/2010/050 to Professor John Herbohn) is gratefully acknowledged. We thank the leaders of Barangay Basper for their permission to work at the Basper Imperata grassland site and the elders of the Manobo tribe for their hospitality and access to their forest. Jone June Bagay, Valentine and Chris Solano, and Ray-An Granada helped in the field and Ofelia Maranguit and Jertz Escala with the laboratory analyses under the supervision of Professor Angela Ferraren (Visayas State University, VSU). We further thank the members of the VSU student team that conducted supplementary infiltration tests at the Basper site in July 2017. Professor Alfredo Lagmay and Miss Maricar Rabonza of the University of the Philippines kindly supplied the DTM-files that enabled the preparation of the site maps. Bob Zwartendijk M.Sc. and Dr. Denyse Snelder (VU University Amsterdam) are thanked for access to their original infiltration data enabling the computation of median values. We thank Dr. Nestor Gregorio (ACIAR project and University of the Sunshine Coast, USC) and Professor Arturo Pasa (VSU) for overall facilitation of the work and Professor John Herbohn (USC) for his continuous support. The constructive comments received from two anonymous reviewers improved the manuscript.
| Funders | Funder number |
|---|---|
| Australian Centre for International Agricultural Research | ASEM/2010/050 |
| Vrije Universiteit Amsterdam | |
| China Scholarship Council |
Keywords
- Hillslope hydrology
- Imperata grassland
- Infiltration
- Overland flow
- Soil degradation
- Soil hydraulic conductivity
- Tropical reforestation
