Alaotra Research Articles

Gullying and landscape evolution: Lavaka in Lac Alaotra, Madagascar shed light on rates of change and non-anthropogenic controls.

Gully evolution remains poorly understood, largely because multidecadal analysis is lacking. Large gullies (called lavaka) that pepper Madagascar's highlands are generally attributed to human impact; but longitudinal data are few, and anthropogenic causation is inferred not verified. We focus on Lac Alaotra, Madagascar's largest lake and wetland, its major rice-growing region, and an ecological hotspot surrounded by fault-controlled steep hills with abundant lavaka. Analysis of historical aerial photographs and recent orthoimagery reveals that the proportion of highly active lavaka has decreased since mid-20th century. At the same time, human population, farming intensity, and livestock density have increased exponentially. This suggests that background factors, including seismicity, are primary drivers of lavaka formation. Although human activities may contribute to erosion overall, land management policies that overemphasize human causation of gullying and neglect background forcing factors (in Madagascar and elsewhere) are unlikely to be effective in erosion mitigation.

Potential and limitations of crowdsourced data for high-resolution rice mapping in Madagascar: The importance of representation

Given the projected population growth and rice consumption in Madagascar, assessing its rice production potential is important. Existing spatial representations of rice are characterized by coarse resolutions and diverge widely. Mapping rice production based on remote sensing offers a potential solution to this problem but its application in Sub-Saharan Africa is hindered by scarce ground truth data and a complex array of cropping systems. While crowdsourcing initiatives provide data that could in principle be used to overcome this hurdle, their usefulness in rice mapping is hitherto underexplored. Here, we investigate the usefulness of crowdsourced data to enhance the mapping of rice production areas in the data-poor context of Madagascar. At present, dedicated crowdsourcing initiatives only limitedly cover rice but do provide sufficient information to build a dataset of data points characterizing a No-Rice class. On the other hand, geotagged pictures from social media, which do document rice production areas, predominantly represent 'scenic' fields appealing to social media contributors, i.e. irrigated, intensive rice production systems. The archetypal nature of these data leads to distinct feature signatures. Consequently, these data could be successfully used for rice mapping in the Lake Alaotra basin, which is characterized by the type of intensive rice cropping that is well-represented by the crowdsourced data. However, it was not possible to construct an accurate map of rice production in the greater Antananarivo region or at the national scale using crowdsourced data as they do not sufficiently represent the present variety in rice production systems. The value of crowdsourced data thus depends on the representativeness of the data, which in turn depends on the application and can be improved through applying a probabilistic sampling design. Our study also highlights the need for data representation checks prior to data augmentation or classification for future applications wanting to construct credible maps using crowdsourcing within their sampling design for which we present a multi-faceted evaluation framework.

A conceptual framework for assessing farmers’ soil knowledge: lessons from the Lake Alaotra Region in Madagascar

Description of the subject. Farmers’ knowledge is a significant source of information about cultivated soil knowledge. Objectives. This paper focuses on farmers in the Alaotra Lake Region in Madagascar to identify their knowledge of the soil and soil fertility and to propose a conceptual framework for developing participatory approaches. Method. The methodology is based on surveys conducted with 100 farmers randomly selected within five Communes (villages) to (i) study their knowledge on soil, (ii) design local soil map, and (iii) identify local soil fertility assessment. For each task, an exploratory survey with non-directive individual interviews followed by more in-depth surveys with semi-directive individual interviews and restitution workshops were conducted. Results. The results revealed two types of local soil classifications according to toposequence. Twelve and nine local soil types were identified respectively in the southern zone and in the northern zone. Moreover, farmers used 14 main local indicators to assess the fertility of these soils. Farmers’ soil classification was found to comply with previous pedological studies and even provided complementary details to the reference French Soil Classification (CPCS). Finally, the local soil fertility indicators have been proved to be identical to those used by other farmers in other countries and are scientifically validated to be effective. Conclusions. This paper offers a new conceptual framework that may be effective for agricultural development service and scientific research in other contexts. It provides a foundation for supporting a common language between farmers and researchers, one that may prove instrumental in future projects including the co-conception of sustainable, innovative agricultural practices.

Vegetation changes and sediment dynamics in the Lake Alaotra region, central Madagascar

Madagascar is known for its high erosion rates in the central highlands, yet the role of human disturbance versus natural processes is not well understood and is a topic of ongoing debate. At present the necessary quantitative data to couple vegetation dynamics and sediment fluxes over time in Madagascar is scarce. This study aims to provide more insight in vegetation changes and sediment transfers over the last millennia in the Lake Alaotra region, and specifically on the role of human disturbances and natural processes. Our vegetation reconstruction is based on pollen records from two lake sediment cores, covering the last 2600 years. Sediment accumulation rates were calculated from cores obtained from the floodplains, from wetlands surrounding the lake, and from Lake Alaotra itself. Our data show an early opening in the landscape, between 2050 and 1700 cal a BP, with a transition from a wooded grassland or woodland/grassland mosaic towards open grassland and an increase in charcoal accumulation rates. (Indirect) human impact is suggested as the main driver for these vegetation changes. Floodplain and wetland sediment accumulation rates only increase in the last 1000 years and peak in the last 400 years. This increased accumulation can mainly be linked to the increased anthropogenic pressure (grazing and farming activities) that triggered increased lavaka (gullies) activity. No changes in accumulation rate were observed in Lake Alaotra, indicating that most sediments are buffered in the floodplains and wetlands. Overall, our pollen and charcoal data suggest an indirect effect of human disturbance on vegetation shifts whilst strong evidence was found for a direct effect of human disturbance on sediment accumulation through intensified use of the grasslands.

Stable isotope profiles of soil organic carbon in forested and grassland landscapes in the Lake Alaotra basin (Madagascar): insights in past vegetation changes

Abstract. The extent to which the central highlands of Madagascar were once covered by forests is still a matter of debate: while reconstructing past environments is inherently difficult, the debate is further hampered by the fact that the evidence documenting land cover changes and their effects on carbon and sediment dynamics in Madagascar has hitherto mainly been derived from lake coring studies. Such studies provide an integrated view over relatively large areas but do not provide information on how land-use change affects hillslopes in terms of carbon and sediment dynamics. Such information would not only be complementary to lake inventories but may also help to correctly interpret lake sediment data. Carbon stable isotope ratios (δ13C) are particularly useful tracers to study the past dynamics of soil carbon over time spans ranging from years to millennia and thus to understand the consequences of land-use change over such time spans. We analysed soil profiles down to a depth of 2 m from pristine forests and grasslands in the Lake Alaotra region in central Madagascar. Along grassland hillslopes, soil organic carbon (SOC) content was low, from 0.4 % to 1.7 % in the top layer, and decreased rapidly to ca. 0.2 % below 100 cm depth. The current vegetation predominantly consists of C4 grasses (δ13C ∼ −13 ‰), yet topsoil δ13C-OC ranges between −23.0 ‰ and −15.8 ‰, and most profiles show a decrease in δ13C-OC with depth. This contrasts with our observations in the C3-dominated forest profiles, which show a typical profile whereby δ13C values increase slightly with depth. Moreover, the SOC stock of grasslands was ∼ 55.6 % lower than along the forested hillslopes for the upper 0–30 cm layer. δ13C values in grassland and forest profiles converge to similar values (within 2.0 ± 1.8 ‰) at depths below ∼ 80 cm, suggesting that the grasslands in the Lake Alaotra region have indeed developed on soils formerly covered by a tree vegetation dominated by C3 plants. We also observed that the percent of modern carbon (pMC) of the bulk OC in the top, middle and lower middle positions of grasslands was less than 85 % near the surface. This could reflect a combination of (i) the long residence time of forest OC in the soil, (ii) the slow replacement rate of grassland-derived OC (iii) and the substantial erosion of the top positions towards the valley position of grasslands. At the valley positions under grassland, the upper 80 cm contains higher amounts of recent grass-derived OC in comparison to the hillslope positions. This is likely to be related to the higher productivity of the grassland valleys (due to higher moisture and nutrient availability), and the deposition of OC that was eroded further upslope may also have contributed. The method we applied, which is based on the large difference in δ13C values between the two major photosynthetic pathways (C3 and C4) in (sub-)tropical terrestrial environments, provides a relatively straightforward approach to quantitatively determine changing vegetation cover, and we advocate for its broader application across Madagascar to better understand the island's vegetation history.

Anogenital scent-marking signals fertility in a captive female Alaotran gentle lemur

The Lake Alaotra gentle lemur (Hapalemur alaotrensis) is one of the 25 most endangered primates in the world and shows low success rate in captive breeding programmes. It is therefore vital to further understand its reproductive biology. We studied a captive troop consisting of five individuals hosted at Jersey Zoo during breeding and non-breeding periods over 1 year. We collected behavioural data (n = 318 h) using all occurrence of some behaviours and ad libitum sampling methods, as well as faecal (n = 54) and anogenital scent (n = 35) samples of the breeding female. We measured sex hormone levels using enzyme immunoassay technique and investigated the volatile component of odour signals using solid-phase microextraction and gas chromatography-mass spectrometry. We observed sexual and aggressive behaviours occasionally during the breeding period. Our regression analysis showed that only period significantly predicted rates of female anogenital scent-marking, whereby the female performed anogenital scent-marking more frequently during the breeding rather than the non-breeding period. In contrast, female hormone levels did not significantly explain variation in rates of neither male nor female olfactory, sexual and affiliative behaviours, suggesting that individuals' behaviour alone is not an effective indicator of the ovulation window. The volatile chemical profile of anogenital odour secretions changed over the study, with four compounds distinguishing the fertile window during the breeding period. In conclusion, our findings suggest that anogenital scent-marking may signal the reproductive status of captive female gentle lemurs.

Comparative analysis of the Copernicus, TanDEM-X, and UAV-SfM digital elevation models to estimate lavaka (gully) volumes and mobilization rates in the Lake Alaotra region (Madagascar)

Abstract. Over the past few decades, developments in remote sensing have resulted in an ever-growing availability of topographic information on a global scale. A recent development is TanDEM-X (TerraSAR-X add-on for digital elevation measurements), an interferometric synthetic aperture radar (SAR) mission of the Deutsche Zentrum für Luft- und Raumfahrt, providing near-global coverage and 12 m resolution digital elevation models (DEMs). Moreover, ongoing developments in uncrewed aerial vehicle (UAV) technology have enabled acquisitions of topographic information at a sub-meter resolution. Although UAV products are generally preferred for volume assessments of geomorphic features, their acquisition remains a time-consuming task and is spatially constrained. However, some applications in geomorphology, such as the estimation of regional or national erosion quantities of specific landforms, require data over large areas. TanDEM-X data can be applied at such scales, but this raises the question of how much accuracy is lost because of the lower spatial resolution. Here, we evaluated the performance of the 12 m TanDEM-X DEM to (i) estimate gully volume, (ii) establish an area–volume relationship, and (iii) determine mobilization rates through comparison with a higher-resolution (0.2 m) UAV structure-from-motion (SfM) DEM and a lower resolution (30 m) Copernicus DEM. We did this for six study areas in the Lake Alaotra region (central Madagascar), where lavaka (gullies) are omnipresent and surface area changes over the period 1949–2010s are available for 699 lavaka. Copernicus-derived lavaka volume estimates were systematically too low, indicating that the Copernicus DEM is too coarse to accurately estimate volumes of geomorphic features at the lavaka scale (100–105 m2). Lavaka volumes obtained from TanDEM-X were similar to UAV-SfM volumes for the largest features, whereas the volumes of smaller features were generally underestimated. To deal with this bias we introduce a breakpoint analysis to eliminate volume reconstructions that suffer from processing errors as evidenced by significant fractions of negative volumes. This elimination allowed the establishment of an area–volume relationship for the TanDEM-X data with fitted coefficients within the 95 % confidence interval of the UAV-SfM relationship. Our calibrated area–volume relationship enabled us to obtain large-scale lavaka mobilization rates ranging between 18 ± 3 and 311 ± 82 tha-1yr-1 for the six different study areas, with an average of 108 ± 26 tha-1yr-1 for the full dataset. These results indicate that current lavaka mobilization rates are 2 orders of magnitude higher than long-term erosion rates. With this study we demonstrate that the global TanDEM-X 12 m DEM can be used to accurately estimate volumes of gully-shaped features at the lavaka scale (100–105 m2), where the proposed breakpoint method can be applied without requiring the availability of a higher-resolution DEM. Furthermore, we use this information to make a first assessment of regional lavaka erosion rates in the central highlands of Madagascar.

Useful plants in the Park Bandro and its surroundings, Lake Alaotra, Madagascar

Traditional use of plants constitutes an important activity in Malagasy life, especially in the countryside. The Sihanaka group is found in the east of Lake Alaotra and is the dominant cultural group in the lake region, including in the Fokontany of Andreba Gara, near Park Bandro, in the east of Lake Alaotra, in Ambatondrazaka district where the study was conducted. The Sihanaka holds traditional knowledge on plant uses and makes use of this knowledge in their daily lives. The objective of this study was to describe the use of aquatic plants in the region to better understand the importance of the Alaotra wetlands in the lives of local people. Surveys conducted among the people of Andreba, including one traditional chief (the Tangalamena) and one healer, revealed 55 useful species of aquatic plants, grouped into 41 genera and 23 families. Most species were used for their medicinal and veterinary virtues (32 species), for animal food (17 species), as utensils and tools (16 species), for cultural uses (10 species), and for human food (9 species). Leaves (76%) are the most exploited plant parts. The species with the most uses were Cyperus papyrus subsp. madagascariensis (Willd.) Kük. with 26 types of use recorded, then Phragmites australis (Cav.) Trin. ex Steud. (19 types of use), Aeschynomene elaphroxylon (Guill. & Perr.) Taub. and Eichhornia crassipes (Mart.) Solms (12 types of use each). Nymphaea nouchali, Cyperus papyrus subsp. madagascariensis and Phragmites australis were the species most frequently cited by informants, indicating that they are important for the local population. The most frequently cited types of use included joro, namely ancestor’s invocation, food, materials for house walls construction, herbal teas to treat ailments, and fencing or demarcation of land boundaries. This study highlighted the importance of the Alaotra wetlands as a source of useful plants for the local population. Sustainable management of Lake Alaotra is therefore not just necessary for biodiversity conservation, but also for maintaining local livelihoods.
 
 L’utilisation traditionnelle des plantes constitue une activité importante dans la vie des Malgaches, plus particulièrement dans les campagnes. Le groupe Sihanaka est rencontré à l’est du lac Alaotra et constitue le groupe culturel dominant dans la région du lac, y compris dans le Fokontany d’Andreba Gara, près du Parc Bandro, à l’Est du Lac Alaotra, dans le district d’Ambatondrazaka où l’étude a été menée. Les Sihanaka détiennent des connaissances traditionnelles sur l’utilisation des plantes et utilisent ces connaissances dans leur vie quotidienne. L’objectif de cette étude était de décrire l’utilisation des plantes aquatiques dans la région afin de mieux comprendre l’importance des zones humides de l’Alaotra dans la vie des populations locales. Des enquêtes menées auprès de la population d’Andreba, y compris auprès d’un chef traditionnel (le Tangalamena) et d’un guérisseur, ont révélé 55 espèces utiles de plantes aquatiques, regroupées dans 41 genres et 23 familles. La plupart des espèces étaient utilisées pour leurs vertus médicinales et vétérinaires (32 espèces), pour l’alimentation des animaux (17 espèces), en tant qu’ustensiles et outils (16 espèces), pour des usages culturels (10 espèces) et pour l’alimentation humaine (9 espèces). Les feuilles (76%) sont les parties de plante les plus exploitées. Les espèces ayant le plus d’utilisations étaient Cyperus papyrus subsp. madagascariensis (Willd.) Kük. avec 26 types d’utilisation recensés, puis Phragmites australis (Cav.) Trin. ex Steud. (19 types d’utilisation), Aeschynomene elaphroxylon (Guill. & Perr.) Taub. et Eichhornia crassipes (Mart.) Solms (12 types d’utilisation chacune). Nymphaea nouchali, Cyperus papyrus subsp. madagascariensis et Phragmites australis etaient les espèces les plus fréquemment citées par les informateurs, ce qui indique qu’elles sont importantes pour la population locale. Les types d’utilisation les plus fréquemment cités comprenaient le joro à savoir l’invocation des ancêtres, l’alimentation, les matériaux pour la construction des murs, les tisanes pour traiter les maladies et la construction de clôtures ou démarcation des limites de terrains. Cette étude a souligné l’importance des zones humides de l’Alaotra en tant que source de plantes utiles pour la population locale. La gestion durable du lac Alaotra n’est donc pas seulement nécessaire à la conservation de la biodiversité mais également au maintien des moyens de subsistance locaux

Under pressure: Rapid lavaka erosion and floodplain sedimentation in central Madagascar

Lavaka (gullies) are often considered as the prime indication of a currently ongoing human-induced environmental crisis in Madagascar's highlands. Yet, lavaka are known to have existed long before human arrival and account for the majority of the long-term sediment input into the highland rivers and floodplains. The role of anthropogenic disturbances in their formation therefore remains highly debated and it is unclear whether lavaka erosion has recently increased. Here, we address these questions by evaluating the dynamics of lavaka in the Lake Alaotra region (central Madagascar). An overall birth to stabilization ratio of 6.1 indicates a rapid lavaka population growth over the period 1949–2010s. Using data on lavaka development we calculated a mean lavaka population age of 410 ± 40 years and estimate that the disequilibrium started at 870 ± 430 cal. BP. Floodplain sedimentation starts to increase around 1000 cal. BP and peaks over the last 400 years, thereby independently confirming this time frame of increased lavaka activity. Lavaka population dynamics modelling shows that a strong increase in environmental pressure over the last centuries is needed to attain current disequilibrium levels. A general drying of the climate since 950 cal. BP in combination with the introduction of cattle and growing human presence around 1000 cal. BP will likely have triggered the increase in lavaka erosion. However, the recent acceleration cannot be explained by climatic changes alone and seems to be linked to increased anthropogenic pressure on the environment. As such, we offer a fresh and quantitatively supported perspective on lavaka dynamics and human impact in central Madagascar, where our methodology can be used in other locations where similar questions on geomorphic equilibrium need to be answered.

From Safety Net to Point of No Return—Are Small-Scale Inland Fisheries Reaching Their Limits?

Small-scale inland fisheries (SSIF) are a livelihood opportunity for millions of people in developing countries. Understanding the economic, ecological, political and social impacts fishers are coping with can clarify weaknesses and challenges in the fishery management. Using the SSIF at Lake Alaotra, Madagascar, as an example, we analyzed the development and fishers’ perception of, and adaptation strategies to, change. We surveyed fish catches to assess the state of fish stocks and conducted interviews to understand fishers’ livelihood, problems, behavior and attitudes. Our results show that the fishery sector of Lake Alaotra has grown dramatically although fish catches have fallen sharply. Changes in species composition and low reproduction rates reflect the fishing pressure. A point of no return seems near, as decreasing agricultural yields force farmers to enter the fishery sector as a form of livelihood diversification. Lake Alaotra reflects an alarming trend which can already be seen in many regions of the world and may affect a growing number in the near future. The Alaotran fisheries demonstrate that SSIF’s ability to provide livelihood alternatives under conditions of insecurity will become increasingly important. It further highlights that the identification of ongoing livelihood dynamics in order to disclose possible poverty trap mechanisms and to understand fisheries’ current function is essential for sustainable management.

Soil survey of the east coast and the central highlands indicates need to update Madagascar soil map

ABSTRACT The soil map of Madagascar has not been substantially updated since the 1960s. The number of reported soil profiles that meet the criteria of the Reference Pedon Description – the highest level of data reliability used to ascertain FAO soil unit classification – is also limited for a country-scale soil map. Therefore, we conducted a soil survey in the east coast and the central highlands, the most populated and major food-producing areas in Madagascar, to assess need for reconsideration of the current soil map. As compared to the latest soil map, our results indicate that Ferralsols cover less area on the flat terrains from the east coast to the central highlands and that Geric Ferralsol is more frequently observed soil type rather than Haplic Ferralsol on acidic rocks. The soil type of paddy fields in the southwestern plain of Lake Alaotra – the country’s largest rice-producing region – was Vertisol with a hydragric horizon rather than Histosol. This is attributed to long-term paddy cultivation in the region or the difference of the definition of peat soils between the current and old soil classification systems. The volcanic-origin soils that sporadically exist in the central highlands can be classified as Eutric Andosol rather than Eutric Cambisol. These results show the need for updating the current soil map based on the quantitative data and also have important implications regarding the land history and for appropriate land management in agriculturally intensive areas in the east coast and central highlands of Madagascar.

Serological Evidence of West Nile and Usutu Viruses Circulation in Domestic and Wild Birds in Wetlands of Mali and Madagascar in 2008.

The geographical distribution and impact on animal and human health of both West Nile and Usutu viruses, two flaviviruses of the Japanese encephalitis complex, have been increasing during the past two decades. Both viruses circulate in Europe and Africa within a natural cycle between wild birds and mosquitoes, mainly from the Culex genus. We retrospectively analyzed sera from domestic and wild birds sampled in 2008 in two wetlands, namely the Inner Niger Delta, Mali, and the Lake Alaotra area, Madagascar. Sera were first tested using a commercial ID Screen West Nile Competition Multi-species ELISA kit. Then, positive sera and sera with insufficient volume for testing with ELISA were tested with a Microneutralization Test. In Mali, the observed seroprevalence in domestic birds was 28.5% [24.5; 32.8] 95%CI, 3.1 % [1.8; 5.2] 95%CI, 6.2% [3.4; 10.2] 95%CI and 9.8 % [7.3; 12.8] 95%CI, for West Nile virus (WNV), Usutu virus (USUV), undetermined flavivirus, and WNV/USUV respectively. Regarding domestic birds of Madagascar, the observed seroprevalence was 4.4 % [2.1; 7.9]95%CI for WNV, 0.9% [0.1; 3.1] 95%CI for USUV, 1.3% [0.5; 2.8] 95%CI for undetermined flavivirus, and null for WNV/USUV. Among the 150 wild birds sampled in Madagascar, two fulvous whistling-ducks (Dendrocygna bicolor) were positive for WNV and two for an undetermined flavivirus. One white-faced whistling-duck (Dendrocygna viduata) and one Hottentot teal (Spatula hottentota) were tested positive for USUV. African and European wetlands are linked by wild bird migrations. This first detection of USUV—as well as the confirmed circulation of WNV in domestic birds of two wetlands of Mali and Madagascar—emphasizes the need to improve the surveillance, knowledge of epidemiological patterns, and phylogenetic characteristics of flavivirus in Africa, particularly in areas prone to sustained, intense flavivirus transmission such as wetlands.

Educational Approaches to Encourage Pro-Environmental Behaviors in Madagascar

Madagascar is a biodiversity hotspot under threat, with about 80% of the population living below the poverty line and dependent on the use of diminishing local resources. Environmental education (EE) can act as an important tool for biodiversity conservation, however, its implementation is challenging in low-income countries. Here, we provide a review of 248 EE interventions throughout Madagascar. We highlight how EE can promote pro-environmental behaviors and show the major obstacles it faces, using Madagascar’s Lake Alaotra as a case study area. All EE activities are implemented by non-governmental organizations (NGOs) and international institutions. EE and community engagement have been shown by practitioners and scientific research alike to be valuable tools but are severely restricted in their impact when their outreach is limited by insecure and insufficient funding, and often funding periods that are too short. Another major hindrance to EE producing positive changes in people’s real-life decisions in low-income countries like Madagascar, arises when lessons are taught to a population that is at once understanding and severely constrained in its choices due to poverty, and corresponding malnutrition, that forces people to make unsustainable decisions on a daily basis. Our conclusions should help to improve the practice of EE in Madagascar and other low-income countries.

Effectiveness of conservation agriculture in increasing crop productivity in low-input rainfed rice cropping systems under humid subtropical climate

Since the early 2000s conservation agriculture (CA) has been promoted in the Lake Alaotra region of Madagascar for a more sustainable and profitable agriculture. There is, however, little known about its performance in low-input rainfed rice-based cropping systems. We conducted a study during two growing seasons (2013/14 and 2014/15) on an experiment that was established in 2009 at the agricultural research station of the National Center for Applied Research and Rural Development (FOFIFA) in the Lake Alaotra region of Madagascar. The experimental setup was a randomized block design with four replications. Two soil/residue management treatments were studied, conventional tillage without residue retention (CT) and no-tillage with residue retention (NT). These two treatments were tested for a 2-year rotation of maize + Dolichos lablab followed by rice (MD//R) and a 3-year rotation of maize + Stylosanthes guianensis, followed by S. guianensis in the second year, and rice in the third year (MS//S//R). During the 2013/14 and 2014/15 seasons, two levels of weed pressure: ‘high’ and ‘low’ were introduced as a split-plot design on the rice plots. The main determining factors of rice yield in the study region were studied: radiation interception, weed infestation, soil moisture and soil mineral nitrogen (N). Our results showed that five to six years of continuous practice of NT with retention of high amounts of crop residues (more than 5 Mg DM ha−1) on the soil surface had a significant (p = 0.02) positive effect on rice yield, irrespective of the level of weed pressure and type of crop rotation. CA systems significantly (p < 0.05) reduced weed density and biomass as compared to CT particularly during the vegetative stage of the rice crop in the two growing seasons, which to a certain extent explained the yield gains under CA. In contrast, treatment effects on soil moisture and mineral N contents were marginal. The positive effects of CA on reduced weed pressure may constitute an important benefit for smallholder farmers, who face labour constraints with hand weeding, and usually cannot afford herbicides for weed control.

Biting the Bullet: Dealing with the Annual Hunger Gap in the Alaotra, Madagascar

The hunger gap (the annual period of hardship when most crops are growing but not yet ready for harvest) remains a reality for many smallholder farmers throughout the globe. With a population largely relying on agriculture, and high poverty and malnutrition rates continuously afflicting the country, farmers in Madagascar are particularly vulnerable to the impacts of the hunger gap, further putting pressure on already fragile ecosystems. Using a case study in the Alaotra region, we examine the seasonal trends of climate and agricultural resource dynamics, as well as characterize farmers’ experiences of and strategies used in response to the hunger gap, in order to assess how conservation may better consider the hunger gap to align its objectives with local needs. Results show that farmers are vulnerable to climatic events during a large part of the year, exacerbating the impacts of the hunger gap. The hunger gap appears to have varying degrees of impact on communities around Lake Alaotra, linked to factors such as road quality and agrarian structures—for example, land tenure and size of parcels—contributing to growing environmental degradation. We end by discussing various past and present responses aimed at improving the resilience of farmers of the Alaotra region, including improved accessibility, agricultural intensification, and conservation agriculture.

An evaluation of the interactions among household economies, human health, and wildlife hunting in the Lac Alaotra wetland complex of Madagascar

In Madagascar, wildlife conservation and human food security and nutrition are deeply interconnected as many people rely on wild foods for sustenance. The Lac Alaotra wetland complex is an ecoregion which is indispensable to both the future food security of Madagascar’s people and the conservation of its endemic wildlife. The region is Madagascar’s largest rice production area, providing thousands of tons of rice and fish to the residents of one of the world’s least food secure nations. The wetland complex also provides habitat to numerous threatened species, including two Critically Endangered mammals found only in the Lac Alaotra wetland complex. Environmental managers must understand how people affect their local environment and how the environment, in turn, affects these people, their livelihoods, and their motivations for future natural resource use. Without an adequate understanding of the complex interactions of local people and their natural environment, it will be impossible to prevent, mitigate, or adapt to future unwanted changes in this complex social-ecological system. We used health assessments of 1 953 residents and semistructured interviews of members of 485 households in 1 9 communities within the Lac Alaotra wetland complex to investigate human-environmental interactions (including current natural resource use and hunting, and how these behaviors affect local economies and human wellbeing). Our team found that, while rates of wildlife consumption were very low throughout the region, the members of 485 surveyed households ate 975 mammals in 2013, including at least 1 6 Alaotra gentle lemurs. Thirteen percent of households had consumed wildlife in 201 3 and less than 1% of hunted wildlife was sold. Employment rates and annual income were both higher than other regions in Madagascar, and food costs were comparatively low. Nevertheless, 98% of households experienced food insecurity, and coping mechanisms (e.g., reducing portion sizes) appear to disproportionately affect young children and non-working members of households. Half of households did not receive the minimum recommended kilocalories per person per day. We found high rates of child malnutrition consistent with national rural statistics. While wildlife consumption does not appear to have significant economic or health benefits in the communities in the Alaotra wetland complex, high food insecurity significantly increased the number of forest and marshland mammals eaten by households. To improve child nutrition and wildlife conservation, we recommend targeted interventions that improve food security.

Conservation Agriculture to buffer and alleviate the impact of climatic variations in Madagascar: farmers’ perception

Conservation Agriculture (CA) has been promoted during the last 15 years in Madagascar to develop a sustainable rainfed agriculture in order to cope with low fertility upland soils, soil erosion, low productivity and erratic rainfall. If CA does provide a better sustainability with adapted cropping patterns when adopted, a question is, whether CA is able to alleviate the impact of climatic variations thanks to the mulching effect and to which extent. We took the example of medium altitude zones in the Lake Alaotra area to illustrate farmers’ perceptions. If climate change is not proven in these areas, climatic variations are very high and erratic rainfall patterns at the beginning of the rainy season induce serious risks of crop failure. Two surveys were implemented in 2013: (i) on CA changing practices of 92 farmers (during the 10 years project duration) and (ii) on the evolution of behavior among 28 farmers who have recently adopted CA (less than 5 years). In CA systems, the mulch contributes to better cropping systems resilience and helps alleviating the effect of climatic variations. If a limited number of farmers have effectively adopted CA practices, in the long run, most farmers have developed innovative cropping systems between conventional agriculture and CA, to address their own constraints, leading to a widespread range of agro-ecological practices. A typology of behavior is presented to identify farmers’ strategies regarding risks in a context characterized by multiple uncertainties.

‘Lake’ Alaotra, Madagascar: A late Quaternary wetland regulated by the tectonic regime

Lake Alaotra, a large but shallow lake in NE Madagascar, has been the focus of prophecies about its future life span. None of the formulated predictions, however, are calibrated against a precisely defined modern limnimetric benchmark or former lake shoreline. As a result, existing scenarios of lake evolution in relation to its surrounding landscape have been predicated on incomplete and uncoordinated information. Here we present a chronology of landscape evolution in the Alaotra Basin based on a coordinated reconstruction of environmental change. The evidence draws upon an inventory of regolith and landforms, hydrological data, a compilation of unpublished boreholes and geophysical surveys of the sedimentary fill sequences, and a record of radiocarbon ages obtained from peat and diatom layers in the stratigraphy. The record indicates that Lake Alaotra has been in existence for at least 30,000 years, with evidence of climatically-driven fluctuations but no evidence of the lake ever being much larger or having occupied the entire floor of the topographic basin. The spatial distribution and sedimentology of the age-bracketed deposits suggest instead that the Alaotra is fundamentally a wetland, or fen, which has been buffering its externally-drained lake from irreversible siltation by heavily loaded streams. The tectonic regime in this distinctly seismic part of Madagascar appears to have regulated basin subsidence and accommodation space, steadily maintaining the basin floor below the level of the water table. If the lake today is under any threat of extinction from excess sediment influx, this is chiefly on account of hydrological alterations to the girdle of fenland by irrigated rice monoculture, with artificial drainage channels recently cut through the wetland buffer and fast-tracking the turbid water of tributary rivers directly to the lake.

Is mulching an efficient way to control weeds? Effects of type and amount of crop residue in rainfed rice based cropping systems in Madagascar

Weeds are a major constraint to crop yields in tropical production systems, especially for smallholder farmers who cannot afford to purchase herbicides. It has been argued that the practice of mulching with crop residues can suppress weeds in conservation agriculture systems. However, few data are available on the effect of crop residue mulching on weed infestation. In this study we quantified the effect of increasing amounts of surface crop residues on weed emergence, weed biomass production and rice yield. The experiment was conducted during four growing seasons in the Lake Alaotra region, Madagascar. Two types of mulch were applied on a no-tilled soil, Stylosanthes guianensis and a mixture of maize and Dolichos lablab, with different amounts ranging from 0 to 45Mg dry matter ha−1. Weed emergence was measured every week from the day of the first rain that triggered weed germination to 100days thereafter, and weed biomass was monitored at four dates during the cropping season. Our results show that weed emergence and weed biomass decreased with increasing amount of residue. More than 10Mgha−1 was, however, needed to significantly reduce weed emergence and weed biomass as compared to the bare soil treatment without surface residues. Rice grain yields decreased by 16% for an increase in weed biomass of one Mgha−1. Our results indicate that mulching is not a viable option of weed control for smallholder farmers, given the low amounts of residue currently retained on their fields, which is at best about 4Mgha−1 in the case of a stylosanthes crop and about 5Mgha−1 in case of dolichos intercropped with maize.

High Energy or Protein Concentrations in Food as Possible Offsets for Cyanide Consumption by Specialized Bamboo Lemurs in Madagascar

Plants producing toxic plant secondary metabolites (PSMs) deter folivores from feeding on them. Animals that can cope with noxious PSMs have a niche with a competitive advantage over other species. However, the ability to cope with toxic PSMs incurs the costs of detoxification. To assess possible compensations for the ingestion of toxic PSMs, we compare the chemical quality of plants consumed by bamboo lemurs (genera Hapalemur and Prolemur; strepsirrhine primates of Madagascar) in areas with and without bamboo. Some bamboo lemurs consume bamboo containing concentrations of cyanogenic substances 10–50 times above the average lethal dosage for mammals, and we postulate that animals consuming cyanogenic substances need supplementary protein or readily available energy for detoxification. We compared the chemical composition of food consumed by three species of bamboo lemurs that feed mainly (>80% of their time) on bamboo in the evergreen rainforest of Ranomafana (Madagascar) with published data of the diets of bamboo lemurs at two sites without highly cyanogenic plants (reed beds of Lac Alaotra and the evergreen littoral forest of Mandena) and with food of sympatric folivorous lemur species that do not feed on bamboo. Lemurs feeding on bamboo consumed up to twice as much protein as bamboo lemurs in areas without bamboo and sympatric lemur species that feed on leaves of trees. Concentrations of nonstructural carbohydrates (a source of energy) showed the opposite trend. This result supports the hypothesis that feeding on cyanogenic plants is linked to high protein intake, either as a source of protein or for sulfur-containing amino acids that can be used for detoxification. Owing to the high protein concentrations in bamboo, however, we cannot distinguish between the hypothesis that lemurs that eat bamboo target additional food items with higher protein from the hypothesis that lemurs feeding on bamboo unavoidably obtain higher concentrations of protein than animals feeding on leaves of trees, without an added nutritional benefit.