Past environmental changes affected lemur population dynamics prior to human impact in Madagascar.

Quaternary climatic changes have been invoked as important drivers of species diversification worldwide. However, the impact of such changes on vegetation and animal population dynamics in tropical regions remains debated. To overcome this uncertainty, we integrated high-resolution paleoenvironmental reconstructions from a sedimentary record covering the past 25,000 years with demographic inferences of a forest-dwelling primate species (Microcebus arnholdi), in northern Madagascar. Result comparisons suggest that climate changes through the African Humid Period (15.2 - 5.5 kyr) strongly affected the demographic dynamics of M. arnholdi. We further inferred a population decline in the last millennium which was likely shaped by the combination of climatic and anthropogenic impacts. Our findings demonstrate that population fluctuations in Malagasy wildlife were substantial prior to a significant human impact. This provides a critical knowledge of climatically driven, environmental and ecological changes in the past, which is essential to better understand the dynamics and resilience of current biodiversity.

Neotectonics and pastoralism: How they impact flood regimes in Madagascar's highlands.

Sustainably maintaining the densely populated upland plains of Madagascar as operationally safe spaces for the food security of the nation and the urban growth of its capital city, Antananarivo, hinges critically on avoiding crop and infrastructure destruction by their through-flowing rivers. The flood regime, however, is also a function of two 'slow' variables hitherto undocumented: tectonic subsidence regime, and floodplain sedimentation rate. From a radiocarbon-dated chronostratigraphy and environmental history of the sediment sequences in three of Madagascar's semi-enclosed upland basins (Antananarivo, Ambohibary, and Alaotra), we quantify and compare how the precarious equilibrium between the two variables entails differentials in accommodation space for sediment and floodwater. Results show that all these plains have been wetlands for at least 40,000 years, but that the Antananarivo Basin is the most vulnerable because the imbalance between sedimentation and subsidence is the largest. Although the tectonic regime and the endemic forms of gully erosion that occur in the catchments are beyond human control, we advocate that flood mitigation strategies should focus on the natural grassland savanna, which makes up most of the contributing areas to surface runoff in the watersheds. Pastoralists are persistently left out of rural development programmes, yet the rangelands could benefit from the introduction of multi-purpose grasses and legumes known to withstand high stocking rates on poor soils while combining the benefits of nutritiousness, fire and drought resistance, with good runoff-arrest and topsoil-retainment abilities. Future-proofing Madagascar's upland grainbaskets and population centres thus calls for joined-up action on the sediment cascade, focusing on soil and water sequestration through integrated watershed management rather than on hard-defence engineering against overflowing rivers on the plains, which has been the costly but ineffectual approach since the 17th century.

Self-amplified Amazon forest loss due to vegetation-atmosphere feedbacks.

Reduced rainfall increases the risk of forest dieback, while in return forest loss might intensify regional droughts. The consequences of this vegetation-atmosphere feedback for the stability of the Amazon forest are still unclear. Here we show that the risk of self-amplified Amazon forest loss increases nonlinearly with dry-season intensification. We apply a novel complex-network approach, in which Amazon forest patches are linked by observation-based atmospheric water fluxes. Our results suggest that the risk of self-amplified forest loss is reduced with increasing heterogeneity in the response of forest patches to reduced rainfall. Under dry-season Amazonian rainfall reductions, comparable to Last Glacial Maximum conditions, additional forest loss due to self-amplified effects occurs in 10-13% of the Amazon basin. Although our findings do not indicate that the projected rainfall changes for the end of the twenty-first century will lead to complete Amazon dieback, they suggest that frequent extreme drought events have the potential to destabilize large parts of the Amazon forest.