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Gond V.,CIRAD - Agricultural Research for Development
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013

African forests within the Congo Basin are generally mapped at a regional scale as broad-leaved evergreen forests, with the main distinction being between terra-firme and swamp forest types. At the same time, commercial forest inventories, as well as national maps, have highlighted a strong spatial heterogeneity of forest types. A detailed vegetation map generated using consistent methods is needed to inform decision makers about spatial forest organization and their relationships with environmental drivers in the context of global change. We propose a multi-temporal remotely sensed data approach to characterize vegetation types using vegetation index annual profiles. The classifications identified 22 vegetation types (six savannas, two swamp forests, 14 forest types) improving existing vegetation maps. Among forest types, we showed strong variations in stand structure and deciduousness, identifying (i) two blocks of dense evergreen forests located in the western part of the study area and in the central part on sandy soils; (ii) semi-deciduous forests are located in the Sangha River interval which has experienced past fragmentation and human activities. For all vegetation types enhanced vegetation index profiles were highly seasonal and strongly correlated to rainfall and to a lesser extent, to light regimes. These results are of importance to predict spatial variations of carbon stocks and fluxes, because evergreen/deciduous forests (i) have contrasted annual dynamics of photosynthetic activity and foliar water content and (ii) differ in community dynamics and ecosystem processes.

Malezieux E.,CIRAD - Agricultural Research for Development
Agronomy for Sustainable Development | Year: 2012

Despite huge gains in productivity, environmental impacts of industrial agriculture based on a few high-yielding crop cultivars and the massive use of chemical fertilisers and pesticides have led to a search for new pathways leading to more sustainable agriculture in both temperate and tropical regions. New strategies incorporating ecological knowledge gained from the observation of natural ecosystems is an alternative to design "ecologically intensive" agroecosystems. Such systems are indeed both ecological and productive. Designing ecologically intensive agroecosystems calls for indepth knowledge of biological regulations in ecosystems, and for the integration of traditional agricultural knowledge held by local farmers. This article reviews the main initiatives underlying ecologically intensive agroecosystems, analyses basic concepts, and proposes a framework for action. The rainforest model, the dry forest model, and the American Prairie are exemplified as three main natural systems at the basis of the mimicry concept. The link between biodiversity and the mimicry hypotheses, and the use of the concepts of productivity, efficiency, stability, and resilience for agroecosystems are discussed. Six main principles for cropping system design based on natural ecosystem mimicry are identified. A three-step framework for action is proposed, including nature observation, experimental design, and participatory design. Although far from being a panacea, the mimicry approach can provide new ways for agroecosystem design both in temperate and tropical countries. © The Author(s) 2011.

Lahmar R.,CIRAD - Agricultural Research for Development
Land Use Policy | Year: 2010

According to KASSA findings, conservation agriculture is less adopted in Europe compared to other adopting regions and, reduced tillage is more common than no-tillage and cover crops. Currently, it is not popularised and it is less researched. The lack of knowledge on conservation agriculture systems and their management and, the absence of dynamic and effective innovation systems make it difficult and socio-economically risky for European farmers to give up ploughing which is a paradigm rooted in their cultural backgrounds. In Norway and Germany the adoption of conservation agriculture has been encouraged and subsidised in order to mitigate soil erosion. In the other European countries the adoption process seems mainly driven by farmers and, the major driving force has been the cost reduction in machinery, fuel and labour saving. Soil and water conservation concerns did not appear as main drivers in the European farmers' decision to shift or not to conservation agriculture. The shift of European farmers to conservation agriculture is being achieved through a step-by-step attitude, large scale farms are the most adopters. This adoption trend may grow in the future. Indeed, the need to improve farms' competitiveness, the market globalization and the steady increase of fuel cost will likely contribute to arouse European farmers' interest in conservation agriculture as it slashes significantly the production costs. Conservation agriculture is not equally suitable for all the European agroecosystems. The need of soil and water conservation in Europe requires anticipating the ongoing process in order to improve its ecological and socio-economic sustainability. Priority would be to define which regions in Europe are the most suitable for conservation agriculture taking into account climate and soil constraints, length of growing period, water availability and quality, erosion hazards and farming conditions. Policy favouring the use of soil cover and profitable crop rotations as management strategies for weed, pest and diseases control will certainly allow developing and disseminating efficient and acceptable conservation agriculture systems. © 2008 Elsevier Ltd. All rights reserved.

This paper gives an overview of the ecosystem model APECOSM (Apex Predators ECOSystem Model) which is developed in the framework of the GLOBEC-CLIOTOP Programme. APECOSM represents the flow of energy through the ecosystem with a size-resolved structure in both space and time. The uptake and use of energy for growth, maintenance and reproduction by the organisms are modelled according to the DEB (dynamic energy budget) theory (Kooijmann, 2000) and the size-structured nature of predation is explicit. The pelagic community is divided into epipelagic and mesopelagic groups, the latter being subdivided into vertically migrant and non-migrant species. The model is mass-conservative. Energy is provided as the basis of the model through primary production and transferred through 3D spatially explicit size-spectra. Focus species (tunas at present, but any predator species can be considered) are "extracted" from the global size-spectra without losing mass balance and represented with more physiological and behavioural details. The forcing effects of temperature, currents, light, oxygen, primary production and fishing are explicitly taken into account. © 2009 Elsevier Ltd. All rights reserved.

Gourlet-Fleury S.,CIRAD - Agricultural Research for Development
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013

Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha-1 greater than or equal to 80 cm DBH) and thinning (11-41 trees ha-1 greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 ± 58.2 Mg ha-1 and 79.7 ± 45.9 m3 ha-1, respectively. We found that (i) natural control forest was increasing in AGB (2.58 ± 1.73 Mg dry mass ha-1 yr-1) and decreasing in timber stock (-0.33 ± 1.57 m3 ha-1 yr-1); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 ± 1.22 Mg ha-1 yr-1) and tripled in the logged + thinned plots (8.03 ± 1.41 Mg ha-1 yr-1); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 ± 0.51 m3 ha-1 yr-1 in the logged plots, and 0.81 ± 0.74 m3 ha-1 yr-1 in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle.

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