When Madagascar produced natural rubber: a brief, forgotten yet informative history.

From 1891 to 1914, Madagascar, like other western African countries, was a production zone for forest rubber destined for export to Europe when Asian plantations where not yet sufficiently developed . Numerous species endemic to the forests of the three major Malagasy ecosystems were exploited, often with a view to maximising short term productivity without any consideration for the sustainable management of the resource. This episode represents one of the first cases of industrial exploitation of Madagascar's biological resources. Although Madagascar occupies a modest position on the world rubber market at that time, the exploitation of rubber bore major consequences for the island's forestry resources and, moreover, influenced the vision and discourse of scientists and politicians concerning their management. It was one of the factors triggering awareness of the value of Madagascar's biodiversity and the threat to which it might be exposed through poorly-controlled human activity. As a result, highly repressive and forcible legislation was introduced aimed at containing the activity practiced by local populations considered to be mostly to blame. But from the early days of French colonial rule, naturalists judged the outcomes of political decisions too weak to offer any guarantee of an effective defence. They responded by adopting an intentionally alarmist and catastrophist discourse with the object of provoking a reaction from the politicians, considered too lax. This discourse, in fact, took an about-turn from 1942-45 when the war effort led to a revitalisation of the Malagasy rubber sector as Asian production was mainly out of reach. A second consequence came in 1927 with the creation of a network of protected areas managed by naturalists, making Madagascar at that time, a pioneer in Africa. There was a simultaneous flurry of activity to promote the domestication of Malagasy rubber species, combined with the introduction of new species with high potential (Hevea brasiliensis, Castilloa elastica). However, with the emergence of far more profitable Asian rubber, all attempts at cultivation in Madagascar were abandoned when exploitation ceased to be profitable, and thus the Malagasy forests were redeemed. This episode demonstrates how it was in fact economic reality, by condemning an unprofitable sector, that was the real vehicle by which the survival of Malagasy rubber species was secured, and not the naturalists' discourse, nor the creation of protected zones, nor the promulgation of repressive legislations. This case study is of more than purely historical interest, in that it still has currency where, for example, the exploitation of Prunus africana is concerned

Chapitre 2. Spatialiser les stocks de carbone

Introduction Dans les laboratoires d’analyse des sols à Madagascar, la mesure du carbone organique du sol (COS) sert à calculer la teneur en matière organique (MO), une information utile pour la gestion de la fertilité des sols. Outre son évaluation quantitative, diverses études sur le COS ont été menées sur (1) sa dynamique, en interaction avec les autres constituants du sol selon les pratiques et modes d’usage des terres ou (2) sur sa variabilité spatio-temporelle. Ces études ont été effect..

Chapitre 7. Stocks de carbone dans les éco- et agrosystèmes à Madagascar

Introduction La quantification du carbone organique des sols (COS) des différents agrosystèmes et écosystèmes naturels est essentielle afin de mieux orienter les stratégies d’adaptation et d’atténuation du changement climatique à différentes échelles : locale, nationale et internationale. Pour un écosystème donné, le COS peut être contenu dans différents compartiments : la biomasse aérienne, la litière, les bois morts, les racines et les sols. Les sols jusqu’à 1 m de profondeur sont reconnus ..

Carbone des sols en Afrique

Les sols sont une ressource essentielle à préserver pour la production d’aliments, de fibres, de biomasse, pour la filtration de l’eau, la préservation de la biodiversité et le stockage du carbone. En tant que réservoirs de carbone, les sols sont par ailleurs appelés à jouer un rôle primordial dans la lutte contre l’augmentation de la concentration de gaz à effet de serre. Ils sont ainsi au centre des objectifs de développement durable (ODD) des Nations unies, notamment les ODD 2 « Faim zéro », 13 « Lutte contre le changement climatique », 15 « Vie terrestre », 12 « Consommation et production responsables » ou encore 1 « Pas de pauvreté ». Cet ouvrage présente un état des lieux des sols africains dans toute leur diversité, mais au-delà, il documente les capacités de stockage de carbone selon les types de sols et leurs usages en Afrique. Il propose également des recommandations autour de l’acquisition et de l’interprétation des données, ainsi que des options pour préserver, voire augmenter les stocks de carbone dans les sols. Tous les chercheurs et acteurs du développement impliqués dans les recherches sur le rôle du carbone des sols sont concernés par cette synthèse collective. Fruit d’une collaboration entre chercheurs africains et européens, ce livre insiste sur la nécessité de prendre en compte la grande variété des contextes agricoles et forestiers africains pour améliorer nos connaissances sur les capacités de stockage de carbone des sols et lutter contre le changement climatique

Mapping organic carbon stocks in eucalyptus plantations of the central highlands of Madagascar : a multiple regression approach

Recent concerns about global warming have resulted in more concerted studies on quantification and modeling of carbon (C) storage in different ecosystems. The aim of this study was to assess and map the carbon stocks in above (ABG), below-ground (BLG) biomass and soil organic carbon contained in the 30 centimeter top-layer (SOC) in coppices of eucalyptus plantations in the central highlands of Madagascar in an area of 1590 ha. Relationships between C stock and various biophysical (stool or shoot stockings and ages, circumferences) and spatial (elevation, slope, and soil type) factors that may affect C storage within each pool were investigated. Three different modeling techniques were tested and compared for various factor sets: (i) simple linear regression (SLM), (ii) multiple linear (MLM) models and, (iii) boosted regression tree (BRT) models. Weights of the factors in the respective model were analyzed for the three pool-specific models that produced the highest accuracy measurement. A regional spatial prediction of carbon stocks was performed using spatial layers derived from a digital elevation model, remote sensing imagery and expert knowledge. Results showed that BRT had the best predictive capacity for C stocks compared with the linear regression models. Elevation and slope were found to be the most relevant predictors for modeling C stock in each pool, and mainly for the SOC. A factor representing circumferences of stools and their stocking (stools.ha(-1)) largely influenced BLG. Shoot circumference at breast height and shoot age were the best factors for ABG fitting. Accuracy assessment carried out using coefficient of determination (R-2) and ratio of standard deviation to prediction error (RPD) showed satisfactory results, with 0.74 and 1.95 for AGB, 0.85 and 2.59 for BLG, and 0.61 and 1.6 for SOC respectively. Application of the best fitted models with spatial explanatory factors allowed to map and estimate C contained within each pool : 32 +/- 13 Gg C for ABG, 67 +/- 15 Gg C for BLG and, 139 +/- 36 Gg C for SOC (1 Gg=10(9) g). A total of 238 +/- 40 Gg C was obtained for the entire study area by combining the three C maps. Despite their relatively low predictive quality, models and C maps produced herein provided relevant reference values of C storage under plantation ecosystems in Madagascar. This study contributed to the reducing of uncertainty related to C monitoring and baseline definition in managed terrestrial ecosystem

Estimating temporal changes in soil carbon stocks at ecoregional scale in Madagascar using remote-sensing

Soil organic carbon (SOC) plays an important role in climate change regulation notably through release of CO2 following land use change such a deforestation, but data on stock change levels are lacking. This study aims to empirically assess SOC stocks change between 1991 and 2011 at the landscape scale using easy-to-access spatially-explicit environmental factors. The study area was located in southeast Madagascar, in a region that exhibits very high rate of deforestation and which is characterized by both humid and dry climates. We estimated SOC stock on 0.1 ha plots for 95 different locations in a 43,000 ha reference area covering both dry and humid conditions and representing different land cover including natural forest, cropland, pasture and fallows. We used the Random Forest algorithm to find out the environmental factors explaining the spatial distribution of SOC. We then predicted SOC stocks for two soil layers at 30 cm and 100 cm over a wider area of 395,000 ha. By changing the soil and vegetation indices derived from remote sensing images we were able to produce SOC maps for 1991 and 2011. Those estimates and their related uncertainties where combined in a post-processing step to map estimates of significant SOC variations and we finally compared the SOC change map with published deforestation maps. Results show that the geologic variables, precipitation, temperature, and soil-vegetation status were strong predictors of SOC distribution at regional scale. We estimated an average net loss of 10.7% and 5.2% for the 30 cm and the 100 cm layers respectively for deforested areas in the humid area. Our results also suggest that these losses occur within the first five years following deforestation. No significant variations were observed for the dry region. This study provides new solutions and knowledge for a better integration of soil threats and opportunities in land management policies

Below-ground biomass production and allometric relationships of eucalyptus coppice plantation in the central highlands of Madagascar

Short rotations of Eucalyptus plantations under coppice regime are extensively managed for wood production in Madagascar. Nevertheless, little is known about their biomass production and partitioning and their potential in terms of carbon sequestration. If above-ground biomass (AGB) can be estimated based on established allometric relations, below-ground (BGB) estimates are much less common. The aim of this work was to develop allometric equations to estimate biomass of these plantations, mainly for the root components. Data from 9 Eucalyptus robusta stands (47-87 years of plantation age, 3-5 years of coppice-shoot age) were collected and analyzed. Biomass of 3 sampled trees per stand was determined destructively. Dry weight of AGB components (leaves, branches and stems) were estimated as a function of basal area of all shoots per stump and dry weight for BGB components (mainly stump, coarse root (CR) and medium root (MR)) were estimated as a function of stump circumference. Biomass was then computed using allometric equations from stand inventory data. Stand biomass ranged from 102 to 130 Mg ha(-1) with more than 77% contained in the BGB components. The highest dry weight was allocated in the stump and in the CR (51% and 42% respectively) for BGB parts and in the stem (69%) for AGB part. Allometric relationships developed herein could be applied to other Eucalyptus plantations which present similar stand density and growing conditions; anyhow, more is needed to be investigated in understanding biomass production and partitioning over time for this kind of forest ecosystem