Your search found 10 records
1 de Rouw, A.. 2001. Weed infestation and soil erosion resulting from the breakdown of the slash and burn cultivation system. In Maglinao, A. R.; Leslie, R. N. (Eds.), Soil erosion management research in Asian catchments: Methodological approaches and initial results - Proceedings of the 5th Management of Soil Erosion Consortium (MSEC) Assembly, held at Semarang, Central Java, Indonesia, 7-11 November 2000. Bangkok, Thailand: IWMI. Southeast Asia Regional Office. pp.85-93.
Soil degradation ; Erosion ; Farming systems ; Traditional farming ; Land use ; Weed control ; Tillage ; Deforestation ; Rice ; Maize ; Cassava / Asia / Thailand / Laos / Vietnam
(Location: IWMI-HQ Call no: IWMI 631.45 G570 MAG Record No: H029249)
2 Valentin, Christian; Agus, F.; Alamban, R.; Boosaner, A.; Bricquet, J. P.; Chaplot, V.; de Guzman, T.; de Rouw, A.; Janeau, J. L.; Orange, Didier; Phachomphonh, K.; Phai, Do Duy; Podwojewski, P.; Ribolzi, O.; Silvera, N.; Subagyono, K.; Thiebaux, Jean-Pierre; Toan, Tran Duc; Vadari, T. 2008. Runoff and sediment losses from 27 upland catchments in Southeast Asia: impact of rapid land use changes and conservation practices. Agriculture, Ecosystems and Environment, 128:225-238.
Runoff ; Sedimentation ; Catchment areas ; Land use ; Erosion ; Upland rice ; Maize ; Cassava ; Shifting cultivation ; Farming systems ; Soil conservation ; Sloping land / Southeast Asia / Indonesia / Laos / Philippines / Thailand / Vietnam
(Location: IWMI HQ Call no: IWMI 631.45 G800 VAL Record No: H041507)
3 Dupin, B.; de Rouw, A.; Phantahvong, K. B.; Valentin, Christian. 2009. Assessment of tillage erosion rates on steep slopes in northern Laos. Soil and Tillage Research, 103(1):119-126. [doi: https://doi.org/10.1016/j.still.2008.10.005]
Tillage ; Erosion ; Shifting cultivation ; Upland rice ; Weed control ; Farming systems ; Sloping land ; Subsistence farming / Laos / Houay Pano Catchment / Luang Prabang District
(Location: IWMI HQ Call no: e-copy only Record No: H041849)
(0.58 MB)
In the hills of south-east Asia shifting cultivation is developing towards more permanent cropping systems. In association with short fallow periods, fields suffer from weed pressure and this, in turn, leads to more frequent and deeper manual tillage. Due to steep slopes these operations induce tillage erosion. Measurements of such soil losses under on-farm conditions are still scarce. In this study tillage erosion was assessed and a predictive model of tillage erosion was established based on slope angle and contact cover, i.e. basal crop area and weed cover. The experiments were conducted in the Houay Pano, Northern Laos. The farmers cultivate annual crops in rotation with 1–3 year fallow periods without external inputs and using only hand tools. Tillage erosion was assessed using the tracer method across nine slope classes (0.30–1.10 m m1) for two crops, upland rice and Job’s tears (Coix lacryma-jobi L.). Soil movement due to land preparation and weeding were assessed separately because different tools are used, a medium size hoe and a small curved hoe. A multivariate regression showed a highly significant relation (R2 = 0.83) between soil losses due to land preparation, slope gradient and contact cover. Predicting models of soil losses due to weeding were also highly significant (R2 = 0.79 for upland rice, R2 = 0.88 for Job’s tears), confirming the importance of tillage erosion on steep slopes (4, 6 and 11 t ha1 year1 on slopes with gradients of 0.30, 0.60 and 0.90 m m1, respectively). Tillage erosion has increased exponentially over the last 40 years because of weed invasion associated with short fallow periods; the initially no-till system has changed into a system heavily dependent on tillage to control weeds and this greatly contributes to soil degradation.
4 Pierret, A.; de Rouw, A.; Chaplot, V.; Valentin, C.; Noble, Andrew; Suhardiman, Diana; Drechsel, Pay. 2011. Reshaping upland farming policies to support nature and livelihoods: lessons from soil erosion in Southeast Asia with emphasis on Lao PDR. [Report of the Management of Soil Erosion Consortium (MSEC) Project]. Marseille, France: Institut de Recherche pour le Developpment (IRD); Colombo, Sri Lanka: International Water Management Institute (IWMI). 40p. [doi: https://doi.org/10.5337/2011.213]
Upland areas ; Farming systems ; Shifting cultivation ; Agricultural policy ; Erosion ; Soil conservation ; Tillage ; Land use ; Site ; Monitoring ; Catchment areas ; Surface runoff ; Riparian zones ; Water management ; Vegetation ; Rain / Southeast Asia / Laos
(Location: IWMI HQ Call no: IWMI Record No: H044693)
(3.98 MB)
5 Lacombe, Guillaume; Ribolzi, O.; de Rouw, A.; Pierret, A.; Latsachak, K.; Silvera, N.; Pham Dinh, R.; Orange, D.; Janeau, J.-L.; Soulileuth, B.; Robain, H.; Taccoen, A.; Sengphaathith, P.; Mouche, E.; Sengtaheuanghoung, O.; Tran Duc, T.; Valentin, C. 2015. Afforestation by natural regeneration or by tree planting: examples of opposite hydrological impacts evidenced by long-term field monitoring in the humid tropics. Hydrology and Earth System Sciences Discussions, 12:12615-12648. [doi: https://doi.org/10.5194/hessd-12-12615-2015]
Afforestation ; Plantations ; Tectona grandis ; Hydrological factors ; Humid tropics ; Ecosystem services ; Land use ; Soil conservation ; Water conservation ; Catchment areas ; Rain ; Runoff ; Models / Lao People s Democratic Republic / Vietnam / Houay Pano Catchment / Dong Cao Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H047340)
http://www.hydrol-earth-syst-sci-discuss.net/12/12615/2015/hessd-12-12615-2015.pdf
https://vlibrary.iwmi.org/pdf/H047340.pdf
https://vlibrary.iwmi.org/pdf/H047340.pdf
(3.39 MB) (3.39 MB)
The humid tropics are exposed to an unprecedented modernization of agriculture involving rapid and highly-mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability controlling habitats, water resources and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydro-meteorological variables has been operating in several headwater catchments in tropical Southeast Asia since 2001. The GR2M water balance model repeatedly calibrated over successive 1 year periods, and used in simulation mode with specific rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses and trend detection tests allowed causality between land-use changes and changes in seasonal flows to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow, led to intricate flow patterns: pluri-annual flow cycles induced by the shifting system, on top of a gradual flow increase over years caused by the spread of the plantation. In Vietnam, the abandonment of continuously cropped areas mixed with patches of tree plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration or planting) led to opposite changes in flow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation.
6 Lacombe, Guillaume; Ribolzi, O.; de Rouw, A.; Pierret, A.; Latsachak, K.; Silvera, N.; Dinh, R. P.; Orange, D.; Janeau, J.-L.; Soulileuth, B.; Robain, H.; Taccoen, A.; Sengphaathith, P.; Mouche, E.; Sengtaheuanghoung, O.; Tran Duc, T.; Valentin, C. 2016. Contradictory hydrological impacts of afforestation in the humid tropics evidenced by long-term field monitoring and simulation modelling. Hydrology and Earth System Sciences, 20:2691-2704.
Humid tropics ; Hydrological factors ; Afforestation ; Natural regeneration ; Plantations ; Monitoring ; Simulation models ; Land use ; Land cover change ; Ecosystem services ; Forest conservation ; Catchment areas ; Rainfall-runoff relationships ; Stream flow ; Cropping systems ; Water conservation ; Soil conservation ; Soil surface properties ; Tectona grandis / Lao People's Democratic Republic / Vietnam / Houay Pano Catchment / Dong Cao Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H047644)
http://www.hydrol-earth-syst-sci.net/20/2691/2016/hess-20-2691-2016.pdf
https://vlibrary.iwmi.org/pdf/H047644.pdf
https://vlibrary.iwmi.org/pdf/H047644.pdf
The humid tropics are exposed to an unprecedented modernisation of agriculture involving rapid and mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability which controls habitats, water resources, and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydrometeorological variables has been operating in several headwater catchments in tropical southeast Asia since 2000. The GR2M water balance model, repeatedly calibrated over successive 1-year periods and used in simulation mode with the same year of rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses, and trend detection tests allowed causality between land-use changes and changes in seasonal streamflow to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow led to intricate streamflow patterns: pluri-annual streamflow cycles induced by the shifting system, on top of a gradual streamflow increase over years caused by the spread of the plantations. In Vietnam, the abandonment of continuously cropped areas combined with patches of mix-trees plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration vs. planting) led to opposite changes in streamflow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation.
7 Ribolzi, O.; Evrard, O.; Huon, S.; de Rouw, A.; Silvera, N.; Latsachack, K. O.; Soulileuth, B.; Lefevre, I.; Pierret, A.; Lacombe, Guillaume; Sengtaheuanghoung, O.; Valentin, C. 2017. From shifting cultivation to teak plantation: effect on overland flow and sediment yield in a montane tropical catchment. Scientific Reports, 7:1-12. [doi: https://doi.org/10.1038/s41598-017-04385-2]
Teak ; Plantations ; Sediment ; Shifting cultivation ; Overland flow ; Erosion ; Slopes ; Land use ; Land management ; Flow discharge ; Vegetation ; Catchment areas ; Rainfall-runoff relationships ; Infiltration ; Soil sampling / Southeastern Asia
(Location: IWMI HQ Call no: e-copy only Record No: H048176)
(2.73 MB)
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-andburn 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.
8 Lacombe, Guillaume; Valentin, C.; Sounyafong, P.; de Rouw, A.; Soulileuth, B.; Silvera, N.; Pierret, A.; Sengtaheuanghoung, O.; Ribolzi, O. 2018. Linking crop structure, throughfall, soil surface conditions, runoff and soil detachment: 10 land uses analyzed in northern Laos. Science of the Total Environment, 616-617:1330-1338. [doi: https://doi.org/10.1016/j.scitotenv.2017.10.185]
Crops ; Soil surface properties ; Erosion ; Runoff ; Sloping land ; Food security ; Plantations ; Vegetation ; Rain ; Infiltration ; Catchment areas ; Land useCrops ; Soil surface properties ; Erosion ; Runoff ; Sloping land ; Food security ; Plantations ; Vegetation ; Rain ; Infiltration ; Catchment areas ; Land use ; Sediment ; Concentrating ; Sediment ; Concentrating / Southeast Asia / Lao People's Democratic Republic
(Location: IWMI HQ Call no: e-copy only Record No: H048341)
In Montane Southeast Asia, deforestation and unsuitable combinations of crops and agricultural practices degrade soils at an unprecedented rate. Typically, smallholder farmers gain income from “available” land by replacing fallow or secondary forest by perennial crops. We aimed to understand how these practices increase or reduce soil erosion. Ten land uses were monitored in Northern Laos during the 2015 monsoon, using local farmers' fields. Experiments included plots of the conventional system (food crops and fallow), and land uses corresponding to new market opportunities (e.g. commercial tree plantations). Land uses were characterized by measuring plant cover and plant mean height per vegetation layer. Recorded meteorological variables included rainfall intensity, throughfall amount, throughfall kinetic energy (TKE), and raindrop size. Runoff coefficient, soil loss, and the percentage areas of soil surface types (free aggregates and gravel; crusts; macro-faunal, vegetal and pedestal features; plant litter) were derived from observations and measurements in 1-m2 micro-plots. Relationships between these variables were explored with multiple regression analyses. Our results indicate that TKE induces soil crusting and soil loss. By reducing rainfall infiltration, crusted area enhances runoff, which removes and transports soil particles detached by splash over non-crusted areas. TKE is lower under land uses reducing the velocity of raindrops and/or preventing an increase in their size. Optimal vegetation structures combine minimum height of the lowest layer (to reduce drop velocity at ground level) and maximum coverage (to intercept the largest amount of rainfall), as exemplified by broom grass (Thysanolaena latifolia). In contrast, high canopies with large leaves will increase TKE by enlarging raindrops, as exemplified by teak trees (Tectona grandis), unless a protective understorey exists under the trees. Policies that ban the burning of multi-layered vegetation structure under tree plantations should be enforced. Shade-tolerant shrubs and grasses with potential economic return could be promoted as understorey.
9 Evrard, O.; Ribolzi, O.; Huon, S.; de Rouw. A.; Silvera, N.; Latsachack, K. O.; Soulileuth, B.; Lefevre, I.; Lacombe, Guillaume; Sengtaheuanghoung, O.; Valentin, C. 2017. Conversion of traditional cropland into teak plantations strongly increased soil erosion in montane catchments of Southeastern Asia [Abstract only] Paper presented at the American Geophysical Union Fall Meeting (AGU), New Orleans, USA, 11-15 December 2017. 1p.
Erosion ; Sediment ; Land use ; Farmland ; Teak ; Plantations ; Catchment areas ; Stream flow ; Vegetation ; Local communities ; Agroforestry / Southeast Asia / Lao People's Democratic Republic
(Location: IWMI HQ Call no: e-copy only Record No: H048619)
Soil erosion delivers an excessive quantity of sediment to rivers of Southeastern Asia. Land use is rapidly changing in this region of the world, and these modifications may further accelerate soil erosion in this area. Although the conversion of forests into cropland has often been investigated, much fewer studies have addressed the replacement of traditional slash-and-burn cultivation systems with commercial perennial monocultures such as teak plantations. The current research investigated the impact of this land use change on the hydrological response and the sediment yields from a representative catchment of Northern Laos (Houay Pano, 0.6 km²) where longterm monitoring (2002-2014) was conducted (http://msec.obs-mip.fr/). The results showed a significant growth in the overland flow contribution to stream flow (from 16 to 31%). Furthermore, sediment yields strongly increased from 98 to 609 Mg km-2. These changes illustrate the severity of soil erosion processes occurring under teak plantations characterized by the virtual absence of understorey vegetation to dissipate raindrop energy, which facilitates the formation of an impermeable surface crust. This counter-intuitive increase of soil erosion generated by afforestation reflects the difficulty to find sustainable production solutions for the local populations of Southeastern Asia. To reduce soil loss under teak plantations, the development of extensive agro-forestry practices could be promoted.
10 Ribolzi, O.; Lacombe, Guillaume; Pierret, A.; Robain, H.; Sounyafong, P.; de Rouw, A.; Soulileuth, B.; Mouche, E.; Huon, S.; Silvera, N.; Latxachak, K. O.; Sengtaheuanghoung, O.; Valentin, C. 2018. Interacting land use and soil surface dynamics control groundwater outflow in a montane catchment of the lower Mekong basin. Agriculture, Ecosystems and Environment, 268: 90-102. [doi: https://doi.org/10.1016/j.agee.2018.09.005]
Hydrology ; Land use ; Soil surface properties ; Soil crusts ; Groundwater recharge ; Flow discharge ; Water level ; Water table ; Catchment areas ; Stream flow ; Models ; Evapotranspiration ; Rain ; Runoff ; Infiltration ; River basins / China / Myanmar / Lao People's Democratic Republic / Thailand / Cambodia / Vietnam / Lower Mekong Basin
(Location: IWMI HQ Call no: e-copy only Record No: H048984)
Groundwater contribution to streamflow sustains biodiversity and enhances ecosystem services, especially under monsoon-driven climate where stream baseflow is often the only available water resource during the dry season. We assessed how land use change influences streamflow and its groundwater contribution in a small headwater catchment subject to shifting cultivation in Montane Southeast Asia. Continuous time series of rainfall, reference evapotranspiration, groundwater level, stream discharge and electrical conductivity (EC) of surface and groundwater were monitored from 2002 to 2007. With the rainfall-runoff model GR4J, we investigated temporal changes in the hydrological behaviour of the study catchment to verify consistencies with observed land use change. An EC-based hydrograph separation method allowed estimating the groundwater contribution to 104 stormflow events. Mean soil surface crusting rates corresponding to each of the nine land uses identified in the catchment were determined using 236 standard 1-m2 micro-plots. Mean plant cover for each land use was assessed in 10 × 10-m2 plots. Bedrock topography and soil layers’ structure were assessed by electrical resistivity tomography to determine pathways of subsurface storm flows. Our results indicate that an increase in the catchment's areal percentage of fallow from 33% to 71% led to a decrease in the annual runoff coefficient from 43% to 26%. The concurrent reduction of soil crusting rate over the catchment, from 48% to 30%, increased rainwater infiltration. Consecutively, groundwater contribution to storm streamflow increased from 83% to 94%, highlighting the protective role of a dense vegetation cover against flash floods. The overall reduction of the annual basin water yield for inter-storm streamflow from 450 to 185 mm suggests that the potential gain in groundwater recharge was offset by the increased root water uptake for evapotranspiration, as confirmed by the drop in the groundwater level. This analysis illustrates how two different land uses with opposite impacts on soil permeability (i/ extensive soil surface crusting under annual crops resulting in limited runoff infiltration or ii/ fallow regrowth promoting both infiltration and evapotranspiration) both inhibit groundwater recharge. The maintenance of strips of fallow buffers between annual crop plots can slow down runoff and locally promote infiltration and groundwater recharge while limiting evapotranspiration.
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