From shifting cultivation to teak plantation: effect on overland flow and sediment yield in a montane tropical catchment

Olivier Ribolzi,Olivier Evrard,Oloth Sengtaheuanghoung,Irène Lefèvre,Bounsamai Soulileuth,Alain Pierret,Anneke De Rouw,Keo Oudone Latsachack,Norbert Silvera,Sylvain Huon,Guillaume Lacombe,Christian Valentin

doi:10.1038/s41598-017-04385-2

Abstract

Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km−2. This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower 137Cs activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.

Highlights

Soil erosion is exacerbated by the intensification of agriculture in montane steep cultivated catchments of Southeastern Asia, where it delivers significant quantities of sediment to rivers[1]
During the last five years of this second sub-period, most of the teak plantations were more than 3 years old and characterised by limited understorey vegetation cover, which may enhance soil degradation
In 2014, land use greatly differed between the two hollow valleys investigated in details (Fig. 1b), with a dominant contribution of typical shifting cultivation landscape mosaics at S7 compared to a major contribution of teak plantations at S8

Summary

Introduction

Soil erosion is exacerbated by the intensification of agriculture in montane steep cultivated catchments of Southeastern Asia, where it delivers significant quantities of sediment to rivers[1] This excessive sediment supply leads to water reservoir siltation[2] and transports particle-bound contaminants towards downstream areas[3,4,5]. To investigate the impact of land-use change on sediment yield, the monitoring of paired catchments is often conducted in nearby sites where contrasted land uses prevail while biophysical characteristics are as similar as possible. This synchronic approach suffers from several limitations because of the difficulty to select two perfectly identical catchments[26]. Discharge and sediment yield were monitored for 13 years in this experimental catchment

Methods

Results

Conclusion