Mekong Floodplains Research Articles

Social Memory in the Mekong’s Changing Floodscapes: Narratives of Agrarian Communities’ Adaptation

Rural adaptation encompasses place-based perceptions, behaviors, livelihoods, and traditional ways of life associated with local environments. These perceptions, norms, and practices are disturbed by coupled environment-development externalities. This study employs the Vietnamese Mekong floodplains as an exemplary case to illustrate how floods impact agrarian communities and how they have experienced flood alterations driven by hydropower development and climate change in recent years. Drawing on thematic and narrative analyses of qualitative data (focus group discussions and interviews) collected in three agrarian communities in the Vietnamese Mekong floodplains, sources drawn from various news outlets, and academic materials, we argue that disrupted flood environments in the floodplains have triggered affective flood reminiscences, catalysing shifts to incremental and transformative adaptation to achieve resilience. We build a nuanced understanding of how social memory helps to enhance human–environment relationships in response to highly complex hydrological dynamics in the delta.

The interrelated impacts of credit access, market access and forest proximity on livelihood strategies in Cambodia

Livelihood diversification strategies in developing countries are influenced by access to financial credit, to markets and to forests. Understanding their interrelated impacts has important implications for development policy, for market access, credit provision, and forest conservation. Using a survey of 2,417 households in 64 villages in four Provinces in Cambodia and satellite data on forest extent, we test hypotheses and quantify the relative contributions and first-order interactions effects of market and road access, forest access, and formal and informal financial credit access on household expenditures and livelihood incomes. We test hypotheses about their statistical interactions, their relative contributions to incomes, and how their effects differ within and outside the Mekong River floodplain. Market and road access are significant with gross income and expenditures, as well as portfolio shifts to off-farm business activities. Forest access contributes significantly to gross income and expenditures. Credit utilization is significant with gross income, expenditures, off-farm business, and livestock activities. Households below the poverty line use financial credit primarily for consumption and agricultural investments, but above the poverty line for business investment and purchasing assets. Market access and financial credit are more important for incomes in the Mekong floodplain area, while forest access is more important outside it. Using dominance analysis, we find that financial credit contributes more than market or forest access to gross income, expenditures, and livestock income. However, market access is more important than credit for off-farm, on-farm and crop incomes, and forest access contributes more to gross income than formal credit access. We also test for first-order interactions between these effects and find they are statistically significant, confirming a synergistic interaction between credit, market and forest access. Market access improves the impact of credit use, as credit use improves gross and off-farm incomes with improved access to large cities, and improves livestock incomes with improved road access. Forests and roads act synergistically to improve household incomes in areas with good city market access, as forest access contributes more to gross income, expenditures and off-farm incomes in areas with good primary road access, and to on-farm incomes in areas with good secondary road access. Our findings show that market, road, credit and forest effects are interconnected and interdependent, but support each other, and significant interaction effects between forest and market access suggest that policies for poverty reduction and forest conservation should be coordinated with the development of roads to improve potential forest returns.

The Cambodian Mekong floodplain under future development plans and climate change

Abstract. Water infrastructure development is considered necessary to drive economic growth in the Mekong region of mainland Southeast Asia. Yet the current understanding of hydrological and flood pattern changes associated with infrastructural development still contains several knowledge gaps, such as the interactions between multiple drivers, which may have serious implications for water management, agricultural production, and ecosystem services. This research attempts to conduct a cumulative assessment of basin-wide hydropower dam construction and irrigation expansion, as well as climate change, implications on discharge, and flood changes in the Cambodian Mekong floodplain. These floodplains offer important livelihoods for a considerable part of the 6.4 million people living on them, as they are among the most productive ecosystems in the world – driven by the annual flood pulse. To assess the potential future impacts, we used an innovative combination of three models: Mekong basin-wide distributed hydrological model IWRM-VMod, with the Mekong delta 1D flood propagation model MIKE-11 and 2D flood duration and extent model IWRM-Sub enabling detail floodplain modelling. We then ran scenarios to approximate possible conditions expected by around 2050. Our results show that the monthly and seasonal hydrological regimes (discharges, water levels, and flood dynamics) will be subject to substantial alterations under future development scenarios. Projected climate change impacts are expected to decrease dry season flows and increase wet season flows, which is in opposition to the expected alterations under development scenarios that consider both hydropower and irrigation. The likely impact of decreasing water discharge in the early wet season (up to −30 %) will pose a critical challenge to rice production, whereas the likely increase in water discharge in the mid-dry season (up to +140 %) indicates improved water availability for coping with drought stresses and sustaining environmental flows. At the same time, these changes would have drastic impacts on total flood extent, which is projected to decline by around 20 %, having potentially negative impacts on floodplain productivity and aquaculture, whilst reducing the flood risk to more densely populated areas. Our findings demonstrate the substantial changes that planned infrastructural development will have on the area, potentially impacting important ecosystems and people's livelihoods, calling for actions to mitigate these changes as well as planning potential adaptation strategies.

A multiplicity ofprek(s): Enacting a socionatural mosaic in the Cambodian upper Mekong delta

In Khmer, the word prek designates a connection between things. In Kandal province in Cambodia, preks crisscross the landscape, connecting rivers with floodplains, supporting rich ecologies and a variety of livelihoods. Drawing on science and technology studies (STS) and critical water research, this paper explores prek(s) as a multiplicity. Rather than taking the prek as a passive object around which various practices occur, we examine how prek(s) are enacted as ontologically different: as irrigation infrastructure, as pathway to rice intensification, as device for Cambodian state-making, and as climate-friendly agricultural development. After analyzing interference patterns between enactments and their scale-making effects in- and outside the Mekong floodplains, we make explicit our own ontological politics. Focused on sustaining multiple uses and ecosystems, “our” prek is a socionatural mosaic landscape where many human and more-than-human actors and practices can coexist. This ontological politics, we suggest, has implications for planetary environmental knowledges and delta management far beyond Kandal’s landscape.

NUMERICAL MODELLING OF SUSPENDED SEDIMENT DYNAMICS IN THE MEKONG DELTA

Delft3D Flexible Mesh (DFM) was used in 2D to compute hydrodynamics and sediment transport in the Mekong Delta. DFM is a process-based model which is solves the two- and three-dimensional shallow equations, based on the finite volume method (Kernkamp et al., 2011).The computational grid covers the entire Mekong Delta, from Kratie, Cambodia to East Sea shelf. It consists of a multi-dimensional grid which includes 1D and 2D combinations. The primary and secondary canals are represented in 1D networks while 2D cells are used for the Mekong River mainstreams, floodplains and shelf. The hydrodynamics results was calibrated and validated by (Thanh et al., 2019). The sediment model was calibrated against the measured data of suspended sediment concentration and fluxes during water year 2011.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/qnKtpFcrMWU

Adaptive flood governance in the Vietnamese Mekong Delta: A policy innovation of the North Vam Nao scheme, An Giang Province

Conventional state policies for intensive agricultural production in the Vietnamese Mekong Delta (VMD) prescribe the expansion of large-scale water engineering infrastructure. In the upper part of the VMD, compounding environmental challenges presented by climate change, hydropower development upstream, and localised development policies have added greater pressures to rural societies, demanding various governance approaches to deal with change. So far, considerable attention has been devoted to policy narratives of how the bureaucratic approach shapes flood management delta-wide, but little is known about the relevant shift towards adaptive governance at the local level. The analysis presented here is based on qualitative data gathered from fieldworks and desk reviews and argues that the North Vam Nao scheme is an exemplary case for policy transformation in the VMD. A hybrid governance paradigm that is characterised by the participatory and hierarchical approaches allows for the shared learning and interactions of knowledge vertically and horizontally among stakeholders. The study presents nuanced implications of the approach in incorporating both ‘integrative’ and ‘adaptive’ components into a long-term water governance strategy, which would serve as a two-pronged contribution to effectively manage environmental uncertainties facing the VMD. It also advocates for the legitimacy of the approach to be institutionalised and widely adopted across the Mekong floodplains and beyond.

Development of a flood water level estimation method using satellite images and a digital elevation model for the Mekong floodplain

ABSTRACTWe have developed a flood water level estimation method that only employs satellite images and a DEM. The method involves three steps: (1) discriminating flood areas and identifying clumps of each flood area, (2) extracting the edges of the identified flood area using a buffering technique, and (3) performing spatial interpolation to transform the extracted elevation to flood water levels. We compared the estimated flood water levels with the observed ones. The RMSE using the RADARSAT was 1.99 and 1.30 m at river and floodplain points, respectively, whereas the RMSE using the MODIS was 4.33 and 1.33 m at the river and floodplain points, respectively. Given that most errors are attributed to the DEM, the method exhibited good performance. Furthermore, the method reproduced the flow directions and flood water level changes during the flooding period. Thus, we demonstrated that the characteristics of flood inundation can be understood even when ground observation data cannot be obtained.

Historical and Operational Monitoring of Surface Sediments in the Lower Mekong Basin Using Landsat and Google Earth Engine Cloud Computing

Reservoir construction and land use change are altering sediment transport within river systems at a global scale. Changes in sediment transport can impact river morphology, aquatic ecosystems, and ultimately the growth and retreat of delta environments. The Lower Mekong Basin is crucial to five neighboring countries for transportation, energy production, sustainable water supply, and food production. In response, countries have coordinated to develop programs for regional scale water quality monitoring that including surface sediment concentrations (SSSC); however, these programs are based on a limited number of point measurements and due to resource limitations, cannot provide comprehensive insights into sediment transport across all strategic locations within the Lower Mekong Basin. To augment in situ SSSC data from the current monitoring program, we developed an empirical model to estimate SSSC across the Lower Mekong Basin from Landsat observations. Model validation revealed that remotely sensed SSSC estimates captured the spatial and temporal dynamics in a range of aquatic environments (main stem of Mekong river, tributary systems, Mekong Floodplain, and reservoirs) while, on average, slightly underestimating SSSC by about 2 mg·L−1 across all settings. The operational SSSC model was developed and implemented using Google Earth Engine and Google App Engine was used to host an online application that allows users, without any knowledge of remote sensing, to access SSSC data across the region. Expanded access to SSSC data should be particularly helpful for resource managers and other stakeholders seeking to understand the dynamics between surface sediment concentrations and land use conversions, water policy, and energy production in a globally strategic region.

Quantifying suspended sediment dynamics in mega deltas using remote sensing data: A case study of the Mekong floodplains

Temporal and spatial concentrations of suspended sediment in floodplains are difficult to quantify because in situ measurements can be logistically complex, time consuming and costly. In this research, satellite imagery with long temporal and large spatial coverage (Landsat TM/ETM+) was used to complement in situ suspended sediment measurements to reflect sediment dynamics in a large (70,000 km2) floodplain. Instead of using a single spectral band from Landsat, a Principal Component Analysis was applied to obtain uncorrelated reflectance values for five bands of Landsat TM/ETM+. Significant correlations between the scores of the 1st principal component and the values of continuously gauged suspended sediment concentration, shown via high coefficients of determination of sediment rating curves (R2 ranging from 0.66 to 0.92), permit the application of satellite images to quantify spatial and temporal sediment variation in the Mekong floodplains. Estimated suspended sediment maps show that hydraulic regimes at Chaktomuk (Cambodia), where the Mekong, Bassac, and Tonle Sap rivers diverge, determine the amount of seasonal sediment supplies to the Mekong Delta. The development of flood prevention systems to allow for three rice crops a year in the Vietnam Mekong Delta significantly reduces localized flooding, but also prevents sediment (source of nutrients) from entering fields. A direct consequence of this is the need to apply more artificial fertilizers to boost agricultural productivity, which may trigger environmental problems. Overall, remote sensing is shown to be an effective tool to understand temporal and spatial sediment dynamics in large floodplains.

Future hydrological alterations in the Mekong Delta under the impact of water resources development, land subsidence and sea level rise

Study regionThe Mekong floodplains and delta are among the most agriculturally productive and biologically diverse waterscapes of the world, but sea level rise, land subsidence, and the proposed upstream development of over 126 hydropower dams and extensive delta-based water infrastructure have raised concern due to potential impacts on the hydrology of the region. Study focusThis study aims to quantify the effects of water infrastructure development, land subsidence and sea level rise on hydrological regimes of the Mekong floodplains and delta through the development and application of a hydrodynamic model. New hydrological insights for the regionDepending on hydrological characteristics of each region (river-dominated, transitional or tidal), the influence of each potential driver may vary. The operation of proposed hydropower dams would change river-dominated upper floodplain’s water levels by 26 to 70% and −0.8 to −5.9% in the dry and wet season respectively, but the impact diminishes throughout the floodplains. In the wet season, the upper Vietnamese Delta changes from a transitional stage to a river-dominated stage, and localized water infrastructure development in the upper delta has the greatest effect on water levels in the region. Land subsidence combined with sea level rise could have the greatest future influence on flooding in the delta if current rates are extrapolated. Sustainable water management strategies are thus necessary to mitigate changes in the floodplains and delta and increase resilience to sea level rise and land subsidence.

Hydrological alterations from water infrastructure development in the Mekong floodplains

AbstractThe Mekong floodplains, which encompasses the region from Kratie Township in Central Cambodia to the Vietnamese East Sea, is a region of globally renown agricultural productivity and biodiversity. The construction of 135 dams across the Mekong basin and the development of delta‐based flood prevention systems have caused public concern given possible threats on the stability of agricultural and ecological systems in the floodplains. Mekong dams store water upstream and regulate flow seasonality, while in situ flood prevention systems re‐distribute water retention capacity in the floodplains. The main aim of this paper is to evaluate possible impacts of the recent development of both hydropower dams and flood prevention systems on hydrological regimes in the Mekong floodplains. An analysis of measured daily and hourly water level data for key stations in the Mekong floodplains from Kratie to the river mouth in Vietnam was conducted. Hydropower dam information was obtained from the hydropower database managed by the Mekong River Commission, and the MODIS satellite imagery was used to detect changes in flooding extent related to the operation of flood prevention systems in the Vietnam Mekong Delta. Results indicate that the upper part of the floodplains, the Cambodian floodplains, may buffer upstream dam impacts to the Vietnam Mekong Delta. Flood prevention up to date has had the greatest effect on the natural hydrological regime of the Mekong floodplains, evidenced by a significant increase of water level rise and fall rates in the upper delta and causing water levels in the middle delta to increase. The development of flood prevention systems has also effected spatial distribution of flooding as indicated via a time series analysis of satellite imagery. While this development leads to increase localized agricultural productivity, our historical data analysis indicates that development of one region detrimentally affects other regions within the delta, which could increase the risk of future conflicts among regions, economic sectors and the ecological value of these important floodplains. Copyright © 2016 John Wiley & Sons, Ltd.

Survey of smallholder beef cattle production systems in different agro-ecological zones of Cambodia

A survey was conducted to better understand the contribution of farm productivity to rural household income and identify differences in production systems, feeding practices and development constraints to smallholder beef cattle producers in the four agro-ecological zones (AEZs) of Cambodia. A semi-structured questionnaire was used to interview 360 households in the four AEZs: I, the Great Lake Floodplain; II, the Mekong Floodplain; III, the Coastal and IV, the Plateau/Mountainous. In addition, samples of common nutritional resources used for cattle feed were collected for nutrient composition analysis, plus cattle were scored for body condition. Rice farming and cattle production were the most common sources of income in all AEZs. The average cattle herd size was 3.7 (SD = 2.4), but the majority of households raised 1-3 animals. The most common cattle management system was grazing with supplementation, mainly with rice straw and 'cut-and-carry' natural grasses fed during the wet season in all AEZs. The body condition score of all cattle types was 3.2 (SD = 0.8), except for cows in lactation that were 1.8. Major constraints to cattle production in AEZs I, II and III were lack of quality feed resources, capital for cattle production and concerns on breed quality, whereas in AEZ IV, diseases were identified as the main constraint. This survey confirms the importance of cattle to smallholders in the four AEZs. Interventions including farmer education to improve husbandry skills, increase the utilisation of forages and crop residues and address disease issues are necessary to enhance cattle production and rural livelihoods in Cambodia.

Dams on Mekong tributaries as significant contributors of hydrological alterations to the Tonle Sap Floodplain in Cambodia

Abstract. River tributaries have a key role in the biophysical functioning of the Mekong Basin. Of particular interest are the Sesan, Srepok, and Sekong (3S) rivers, which contribute nearly a quarter of the total Mekong discharge. Forty two dams are proposed in the 3S, and once completed they will exceed the active storage of China's large dam cascade in the Upper Mekong. Given their proximity to the Lower Mekong floodplains, the 3S dams could alter the flood-pulse hydrology driving the productivity of downstream ecosystems. Therefore, the main objective of this study was to quantify how hydropower development in the 3S, together with definite future (DF) plans for infrastructure development through the basin, would alter the hydrology of the Tonle Sap's Floodplain, the largest wetland in the Mekong and home to one of the most productive inland fisheries in the world. We coupled results from four numerical models representing the basin's surface hydrology, water resources development, and floodplain hydrodynamics. The scale of alterations caused by hydropower in the 3S was compared with the basin's DF scenario driven by the Upper Mekong dam cascade. The DF or the 3S development scenarios could independently increase Tonle Sap's 30-day minimum water levels by 30 ± 5 cm and decrease annual water level fall rates by 0.30 ± 0.05 cm day−1. When analyzed together (DF + 3S), these scenarios are likely to eliminate all baseline conditions (1986–2000) of extreme low water levels, a particularly important component of Tonle Sap's environmental flows. Given the ongoing trends and large economic incentives in the hydropower business in the region, there is a high possibility that most of the 3S hydropower potential will be exploited and that dams will be built even in locations where there is a high risk of ecological disruption. Hence, retrofitting current designs and operations to promote sustainable hydropower practices that optimize multiple river services – rather than just maximize hydropower generation – appear to be the most feasible alternative to mitigate hydropower-related disruptions in the Mekong.

Historical impact of water infrastructure on water levels of the Mekong River and the Tonle Sap system

Abstract. The rapid rate of water infrastructure development in the Mekong Basin is a cause for concern due to its potential impact on fisheries and downstream natural ecosystems. In this paper, we analyze the historical water levels of the Mekong River and Tonle Sap system by comparing pre- and post-1991 daily observations from six stations along the Mekong mainstream from Chiang Saen (northern Thailand), to Stung Treng (Cambodia), and the Prek Kdam station on the Tonle Sap River. Observed alterations in water level patterns along the Mekong are linked to temporal and spatial trends in water infrastructure development from 1960 to 2010. We argue that variations in historical climatic factors are important, but they are not the main cause of observed changes in key hydrological indicators related to ecosystem productivity. Our analysis shows that the development of mainstream dams in the upper Mekong Basin in the post-1991 period may have resulted in a modest increase of 30-day minimum levels (+17%), but significant increases in fall rates (+42%) and the number of water level fluctuations (+75%) observed in Chiang Saen. This effect diminishes downstream until it becomes negligible at Mukdahan (northeast Thailand), which represents a drainage area of over 50% of the total Mekong Basin. Further downstream at Pakse (southern Laos), alterations to the number of fluctuations and rise rate became strongly significant after 1991. The observed alterations slowly decrease downstream, but modified rise rates, fall rates, and dry season water levels were still quantifiable and significant as far as Prek Kdam. This paper provides the first set of evidence of hydrological alterations in the Mekong beyond the Chinese dam cascade in the upper Mekong. Given the evident alterations at Pakse and downstream, post-1991 changes could also be directly attributed to water infrastructure development in the Chi and Mun basins of Thailand. A reduction of 23 and 11% in the water raising and falling rates respectively at Prek Kdam provides evidence of a diminished Tonle Sap flood pulse in the post-1991 period. Given the observed water level alterations from 1991 to 2010 as a result of water infrastructure development, we can extrapolate that future development in the mainstream and the key transboundary Srepok, Sesan, and Sekong sub-basins will have an even greater effect on the Tonle Sap flood regime, the lower Mekong floodplain, and the delta.

Reappraisal of sediment dynamics in the Lower Mekong River, Cambodia

ABSTRACTThe Mekong Basin in southeast Asia is facing rapid development, impacting its hydrology and sediment dynamics. Although the understanding of the sediment transport rates in the Mekong is gradually growing, the sediment dynamics in the lower Mekong floodplains (downstream from Kratie) are poorly understood. The aim of this study is to conduct an analysis to increase the understanding of the sediment dynamics at the Chaktomuk confluence of the Mekong River, and the Tonle Sap River in the Lower Mekong River in Cambodia. This study is based on the data from a detailed field survey over the three hydrological years (May 2008–April 2011) at the two sites (the Mekong mainstream and the Tonle Sap River) at the Chaktomuk confluence. We further compared the sediment fluxes at Chaktomuk to an upstream station (i.e. Mukdahan) with longer time series. Inflow sediment load towards the lake was lower than that of the outflow, with a ratio on average of 84%. Although annually only a small amount of sediment load from the Tonle Sap contributes to the delta (less than 15%), its share is substantial during the February–April period. The annual sediment load transport from the confluence to the delta in 2009 and 2010 accounted for 54 and 50 Mt, respectively. This was on average only 55% of the sediment fluxes measured at Mukdahan, a more upstream station. Furthermore when compared to sediment loads further downstream at the Cambodia–Vietnam border, we found that the suspended sediment flux continued to decline towards the South China Sea. Our findings thus indicate that the sediment load to the South China Sea is much lower than the previous estimate 150–160 Mt/yr. Copyright © 2014 John Wiley & Sons, Ltd.

Resistance versus resilience approaches in road planning and design in delta areas: Mekong floodplains in Cambodia and Vietnam

Engineering works in river basins that explicitly take into account floodplain hydraulic processes and dynamics, demonstrate a move towards more sustainable development in riparian areas. In this paper, this concept is applied to road planning and design in floodplains. The paper suggests that although a resilience strategy might require higher initial investments than a resistance strategy, in the longer term it will result in lower costs in terms of road damage and ecological damage. Results are presented from four cases in the Mekong floodplains where different strategies towards road planning, varying in resilience, have been assessed for their hydraulic, ecological, social and economic impacts based on a combination of modelling results, expert judgement and secondary data sources. The study finds that, with the exception of extreme cases, the impact of roads has a limited impact on the floodplain hydraulics. However, even small changes in flood dynamics (arrival of the peak, duration) may have large ecological impacts, especially if cumulative impacts of more road developments are taken into account. The results illustrate that road planning and design in floodplains is a complicated task that requires an integrated approach.

Cumulative impacts of road developments in floodplains

This paper investigates the impact of differing road development strategies in floodplains for increasing levels of road expansion, focusing on hydraulic characteristics of floods such as water level, velocity and inundation duration and extent. Cumulative impacts are presented in term of both a resistant approach where road transport infrastructure has the secondary purpose of flood dykes and, a resilience approach that maintains the floodplain hydraulics through the use of flow through structures. Each method is examined in the context of road development in the Cambodian Mekong floodplain. Results indicate that resistance approaches necessitate higher levels of road structures, designed to higher technical specifications, whilst resilience approaches maintain the hydraulic character of floodplains but require the inclusion of well-designed flow through structures with localized scour protection.

Modelling climate change impacts on the flood pulse in the Lower Mekong floodplains

The flood pulse is a key element characterizing the hydrology of the Mekong River and driving the high ecosystem productivity in the Lower Mekong floodplains, both in the Cambodian lowlands and the Mekong Delta in Vietnam. This paper assesses the impacts of climate change, both in terms of changed basin water balance and sea level rise, on the Lower Mekong flood pulse. The impacts were simulated by a three-dimensional hydrodynamic model using the projected changes in sea level and the Mekong mainstream discharge under the influence of climate change as boundary conditions. The model simulations projected that average and maximum water levels and flood duration increase in 2010–2049. The most consistent and notable changes occurred in the average and dry hydrological years. Sea level rise had the greatest effects in the Mekong Delta, whereas the impacts of changed basin water balance were more notable in the upper areas of the Mekong floodplains. The projected impacts were mostly opposite to those resulting from regional water infrastructure development. Higher and longer flooding could cause damage to crops, infrastructure and floodplain vegetation, and decrease the fertile land area. On the other hand, it might boost ecosystem productivity and enhance dry season water availability.

Struggle in the flood: tree responses to flooding stress in four tropical floodplain systems.

In the context of the 200th anniversary of Charles Darwin's birth in 1809, this study discusses the variation in structure and adaptation associated with survival and reproductive success in the face of environmental stresses in the trees of tropical floodplains. We provide a comparative review on the responses to flooding stress in the trees of freshwater wetlands in tropical environments. The four large wetlands we evaluate are: (i) Central Amazonian floodplains in South America, (ii) the Okavango Delta in Africa, (iii) the Mekong floodplains of Asia and (iv) the floodplains of Northern Australia. They each have a predictable 'flood pulse'. Although flooding height varies between the ecosystems, the annual pulse is a major driving force influencing all living organisms and a source of stress for which specialized adaptations for survival are required. The need for trees to survive an annual flood pulse has given rise to a large variety of adaptations. However, phenological responses to the flood are similar in the four ecosystems. Deciduous and evergreen species respond with leaf shedding, although sap flow remains active for most of the year. Growth depends on adequate carbohydrate supply. Physiological adaptations (anaerobic metabolism, starch accumulation) are also required. Data concerning the ecophysiology and adaptations of trees in floodplain forests worldwide are extremely scarce. For successful floodplain conservation, more information is needed, ideally through a globally co-ordinated study using reproducible comparative methods. In the light of climatic change, with increasing drought, decreased groundwater availability and flooding periodicities, this knowledge is needed ever more urgently to facilitate fast and appropriate management responses to large-scale environmental change.

Folk medicine in Laos: A comparison between two ethnic groups

Folk healing was studied in two ethnic groups of Laos during the period 1965–75. Hmong, mostly illiterate and animistic, lived in highly autonomous villages within an atomistic society, occupying remote and sparsely populated mountains. Lao, mostly literate and Buddhist, lived in lowland towns and villages within a hierarchical and integrated society, occupying the densely populated Mekong flood plain. Folk healing systems of both groups demonstrated similarities regarding folk syndromes and folk modalities. Differences included more complex theories about illness, greater number of folk practitioner types and greater differentiation of the shaman role (i.e. into separate priest and healer roles) in the more complex Lao society.