Agroforesterie et services écosystémiques en zone tropicale

Respectueux de l’environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu’ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d’agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu’à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L’ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d’une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l’Est et du Centre, d’autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d’Afrique de l’Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l’IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L’ensemble de ces projets s’articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent

Relevance of secondary tropical forest for landscape restoration

Tropical Secondary Forests (SFs) are vulnerable forest systems growing in areas that have been subject to unsustainable human activities leading to deforestation. SFs account for swathes of tropical forest landscapes that have lost their capacity to provide a high level of goods and services. They are also located in highly dynamic and human-pressured landscapes and are vulnerable to natural and human-induced catastrophic events, such as hurricanes or fires. Without appropriate silvicultural management to increase their economic value and restore their ecological functions, they often become degraded and are sometimes cleared for more short-term economically productive activities. Given the increasing demand for tropical timber in recent decades that will continue in the near future, we suggest that active restoration geared towards wood production is an opportunity for SF conservation. Promoting sustainable wood production -i.e. associated with other environmental services- in these disturbed forest ecosystems is also a way to reduce logging pressure on the remaining intact primary tropical forests, indeed, this may be the most important reason to enhance active restoration aimed at wood production in tropical SFs worldwide. Future research in forest ecology and management should produce experimental evidence of enhanced production of wood and ecosystem services in SFs through appropriate silvicultural experimentations

Biomass of timber species in Central American secondary forests: Towards climate change mitigation through sustainable timber harvesting

Sustainable management of secondary forests for timber production offers the opportunity to combine nature-based climate change mitigation with direct improvement of human livelihoods in the tropics, but this dual potential has rarely been explored. We characterized aboveground biomass (AGB) in secondary forests (SF) in Nicaragua and Costa Rica in whole stands (ecological potential), individual trees of timber species (total timber potential), and currently harvestable timber (harvestable timber potential). We also linked the three types of AGB potential to climate and soil factors. Data on 302 sample plots were collected, most from national forest inventories (NFIs) concerning 168 plots in Nicaragua and 134 plots in Costa Rica

Spatiotemporal pattern analysis of Cacao swollen shoot virus in experimental plots in Togo

In order to quantitatively analyse the spatial pattern of cacao swollen shoot disease, particularly in cases of re-emergence, three experimental plots were installed in a diseased area of cacao cv. Amelonado in Togo. After thorough cleaning and grubbing, the three plots were planted with less susceptible, hybrid plant material. Twenty years after replanting, a survey of healthy, diseased and dead trees was carried out during 2 consecutive years. Data were analysed using Ripleys functions and join counts analysis. The re-emergence of the disease occurred in patches or foci: following analyses with the two statistical methods, diseased trees and dead trees were found to be clearly aggregated on the three observed plots for the 2 years. The observed progress of the disease was not the same on the three plots and seemed dependent on the disease state of the first year: the higher the attack rate of the first year, the faster the disease progression. The use of less susceptible plants helped keep the land productive for 15 years. In conclusion, uprooting of the first infection focus can extend the life of cacao plots

Use of CAF2007, a process-based model of coffee agroforestry systems, to represent and understand the evolution of coffee productivity in two long term trials in Mesoamerica

International audienceCoffee is frequently cultivated under shade in Mesoamerica. The effects of shade trees on coffee productivity depend on the environmental conditions: mainly temperature, humidity, solar radiation and rainfall patterns. Crop models may be useful to assess current systems and modify their shade management, to improve productivity and provision of environmental services. The CAF2007 model was recently developed to simulate coffee growth and yield elaboration under shade at plot scale, under Mesoamerican environmental and technical conditions. The model was first compared with the scientific and local knowledge on coffee productivity under shade. Our results show that coffee phenology is correctly accounted for in the model, although the module that simulates the effects of light and water stress on flowering needs adjustment. The water module, carbon accumulation module and N balance module were then tested in coffee plantations, using 2 experimental data sets. When adequately parameterized, the modules did simulate correctly the variables measured, with a few exceptions. Proposals were formulated to develop or modify modules, to improve the simulations. The model was then parameterized to reproduce 2 data sets from two 7-year-old experiments of CATIE, with coffee cultivated under diverse shade trees and N management: one in Turrialba, Costa Rica, under humid conditions, with no definite dry season, and one in Masatepe, Nicaragua, with a very pronounced dry season. The model was able to reproduce the evolution of coffee bean production and the accumulation of biomass in the experiments. Functional explanations for observed evolutions, related to excessive shade and to insufficient N inputs, were proposed from the model. The implications of these results for future model improvement and applicability are discusse

Above-ground biomass storage potential in primary rain forests managed for timber production in Costa Rica

Tropical forests play a fundamental role in mitigating climate change through storage of carbon in above- and below- ground biomass. Their mitigation potential is, however, affected by significant greenhouse gas emissions through tropical deforestation or forest degradation. Mitigating degradation caused by conventional logging is therefore an important challenge for silvicultural management, and various reduced impact logging techniques seek to reduce biomass loss and other logging impacts during forest logging activities. Little knowledge exists about the potential of sustainable management for maintaining and restoring the climate change mitigation capacity of tropical forests. Our research contributes to knowledge about this potential, as our aim is to evaluate the above-ground biomass (AGB) stock of tropical forests managed for sustainable timber production and compare it with that of intact primary forests. We also determine the environmental and spatial factors that influence AGB