Madagascar corals reveal a multidecadal signature of rainfall and river runoff since 1708

Pacific Ocean sea surface temperatures (SST) influence rainfall variability on multidecadal and interdecadal timescales in concert with the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO). Rainfall variations in locations such as Australia and North America are therefore linked to phase changes in the PDO. Furthermore, studies have suggested teleconnections exist between the western Indian Ocean and Pacific Decadal Variability (PDV), similar to those observed on interannual timescales related to the El Niño Southern Oscillation (ENSO). However, as instrumental records of rainfall are too short and sparse to confidently assess multidecadal climatic teleconnections, here we present four coral climate archives from Madagascar spanning up to the past 300 yr (1708–2008) to assess such decadal variability. Using spectral luminescence scanning to reconstruct past changes in river runoff, we identify significant multidecadal and interdecadal frequencies in the coral records, which before 1900 are coherent with Asian-based PDO reconstructions. This multidecadal relationship with the Asian-based PDO reconstructions points to an unidentified teleconnection mechanism that affects Madagascar rainfall/runoff, most likely triggered by multidecadal changes in North Pacific SST, influencing the Asian Monsoon circulation. In the 20th century we decouple human deforestation effects from rainfall-induced soil erosion by pairing luminescence with coral geochemistry. Positive PDO phases are associated with increased Indian Ocean temperatures and runoff/rainfall in eastern Madagascar, while precipitation in southern Africa and eastern Australia declines. Consequently, the negative PDO phase that started in 1998 may contribute to reduced rainfall over eastern Madagascar and increased precipitation in southern Africa and eastern Australia. We conclude that multidecadal rainfall variability in Madagascar and the western Indian Ocean needs to be taken into account when considering water resource management under a future warming climate

Diversité de la macrofaune des sols cultivés sur les Hautes-Terres de Madagascar

Crop management and soil macrofauna diversity in the Highlands of Madagascar. Description of the subject. This article deals with soil macrofauna as a key component of soil biological functioning. Objectives. This original study, performed in 2015, aimed to compare the effect of contrasted land uses and cultural practices on soil macrofauna in a crop-livestock area in the Madagascar Highlands. Five cropping systems were investigated: annual crops under tillage with low (LAMF) and high (LAEF) manure inputs, permanent tilled forage crops with high manure inputs (CFEF), crops under conservation agriculture without tillage or permanent mulch cover and with medium manure inputs (ACMF), and permanent pastures without tillage and without manure (PP0F). Method. In each of these five cropping systems, soil macrofauna was sampled in 12 plots from experimental trials and smallholder farms at the end of the rainy season. In each plot, soil macrofauna was hand-sorted from five soil monoliths at a 0-30 cm depth. Results. Fifty-two species were identified and organized into 15 orders and six functional groups. In the annual cropping systems (ACMF), the absence of tillage and the presence of a permanent soil cover increased soil macrofauna diversity and density without reducing harmful white grubs (Scarabeoid beetle larvae), while earthworm density was reduced in comparison with the CFEF system. In conventional tillage cropping systems, manure input intensity (LAMF versus LAEF) had no specific effects on white grubs or earthworms. Conclusions. This study on soil macrofauna in the Highlands of Madagascar helped to establish which agricultural practices and farming systems are favourable to beneficial soil invertebrates such as earthworms, and unfavourable to harmful insects such as white grubs. This will help farmers to achieve a more sustainable crop management

Scarabaeoidea larvae (Insecta, Coleoptera) in rainfed rice fields in medium and high altitude areas of Central Madagascar.

International audienceLarvae (white grubs) of many scarab beetle species can be found in rainfed rice fields in medium and high altitude areas of Madagascar, with certain species being pests. For pest management, it is therefore critical to be able to accurately identify them. Raster morphology makes it possible to determine the difference between species. Twenty six larvae morpho-species were thus distinguished, of which 18 species, whose larvae and pupae were unknown, were identified after development to adults: Bricoptis, Celidota, Anochilia, Euryomia (Cetoniidae, four species), Heteronychus, Hexodon, Heteroconus, Paranodon (Dynastidae, seven species), Paramorphochelus (Hopliidae, one species), Encya, Enaria, Apicencya, Empecta, Hoplochelus (Melolonthidae, five species) and Triodontus (Orphnidae, one species). Original descriptions of third instar larvae of 17 species, and of pupae of 13 of them are given, along with an identification key of 25 larvae morpho-species. Pupae external genitoanal structures concept is defined. All diagnostic traits are illustrated

Candidate plants to help soil pest control in conservation agriculture: potential effects of 21 species used as cover crops in Madagascar

International audienc

Les vers blancs du riz pluvial d'altitude (Col. Scarabaeoidea) à Madagascar : effets de la plante-hôte et de la matière organique du sol sur le comportement larvaire

Sur les Hauts-Plateaux malgaches, les vers blancs (Coleoptera : Scarabaeoidea), représentés par de nombreuses espèces, sont considérés comme des ravageurs majeurs du riz pluvial. Toutefois, cette perception est partiellement erronée, la relation de ces insectes à la culture variant selon les espèces et le statut organique du sol. En microcosmes au laboratoire, les larves du Cetoniidae Bricoptis variolosa et du Dynastidae Hexodon unicolor unicolor ont présenté un régime saprophage strict, ne causant jamais aucun dommage à la culture. Celles du Melolonthidae Apycencya sp. nov. se sont montrées strictement rhizophages, et celles des Dynastidae Heteronychus spp (H. plebejus, H. bituberculatus et H. arator rugifrons) et Heteroconus paradoxus rhizophages facultatives, ne s'attaquant aux racines de riz qu'en sols pauvres en matière organique. Chez H. arator rugifrons et H. paradoxus, un effet phagostimulant du fumier de bovin a été mis en évidence, se traduisant par un gain de poids des larves significativement plus élevé dans du sol additionné de paille de riz, en présence de sacs de toile remplis de fumier vs de sol seul ou de sol imprégné d'humus liquide. Ces résultats ouvrent de nouvelles perspectives de gestion des vers blancs, particulièrement avec les systèmes en semis direct sur couverture végétale (SCV). (Résumé d'auteur

Earthworm Functional Groups, Residue Quality and Management Impact on Upland Rice Growth and Yield – An Experimental Study in the Madagascar Highlands

International audienceAims: In Madagascar, agroecological practices to increase and sustain upland rice productivity are based on an intensification of soil ecological processes. Study Design: The effects of earthworm presence and identity (Pontoscolex corethrurus, Dichogaster saliens, or no earthworms), residue presence and identity [Crotalaria grahamiana (Fabaceae), Desmodium uncinatum (Fabaceae), Stylosanthes guianensis (Fabaceae), Eleusin

Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar

Coral cores provide vital climate reconstructions for site-specific temporal variability in river flow and sediment load. Yet, their ability to record spatial differences across multiple catchments is relatively unknown. Here, we investigate spatial linkages between four coral proxies of terrestrial runoff and their relationships between sites. Coral cores were drilled in and around Antongil Bay, the largest bay in Madagascar, and individually analysed for fifteen years of continuous luminescence (G / B), Ba / Ca, δ<sup>18</sup>O<sub>sw</sub> and δ<sup>13</sup>C data. Each coral core was drilled close to individual river mouths (≥ 7 km), and proxy data were compared to modelled river discharge and sediment runoff data for the three corresponding catchments. A reasonable agreement between terrestrial runoff proxies with modelled river discharge and sediment yield was observed. Some inconsistencies between proxy and modelled data are likely linked to proxy behaviour, watershed size and local environmental physiochemical parameters. In general, the further a coral resided from its river source, the weaker the proxy relationship was with modelled data and other corals, due to mixing gradients and currents. Nevertheless, we demonstrate that two coral Ba / Ca and luminescence (G / B) records influenced by the same watershed are reproducible. Furthermore, a strong Ba / Ca relationship was observed between two cores from distant watersheds, with baseline averages in agreement with modelled sediment runoff data. As humic acids behave conservatively in the water column, luminescence (G / B) data gave the highest regional correlations between cores, and showed the most consistent relationship with site specific modelled discharge. No statistical relationship was observed between cores in terms of interannual δ<sup>18</sup>O<sub>sw</sub> and δ<sup>13</sup>C, meaning corals were recording a localised signal at their respective sites, confounded by vital effects. Comparing proxy baseline averages and mean seasonal cycles provided a good overview of the runoff dynamics of the bay system

Earthworm Functional Groups, Residue Quality and Management Impact on Upland Rice Growth and Yield – An Experimental Study in the Madagascar Highlands

International audienceAims: In Madagascar, agroecological practices to increase and sustain upland rice productivity are based on an intensification of soil ecological processes. Study Design: The effects of earthworm presence and identity (Pontoscolex corethrurus, Dichogaster saliens, or no earthworms), residue presence and identity [Crotalaria grahamiana (Fabaceae), Desmodium uncinatum (Fabaceae), Stylosanthes guianensis (Fabaceae), Eleusin