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In 2000, CATIE began a long-term coffee agroforestry trial aimmg to research complex interactions among climate, soil, shade trees, managements, and coffee varieties, useful for the development of systems that enhance soil ecological restoration, biodiversity, and ecosystem services. The trial consists of combinations of shade and managements: six types of shade from associations of legume and timber trees, and full-sun systems, combined with four managements (high conventional (AC), moderate conventional (MC), intensive organic (MO) and low organic (BO)), resulting in >20 types of systems, in which traditional and improved coffee varieties are also being tested. More than 30 research centers and universities have been involved to produce >30 scientific papers, >40 theses, and >20 technical documents. The revision of the main fmdings indicates that full sun systems (AC, MC) produce high yields but with a trade-off on ecosystem services provision; while agroforestry systems with legume trees, especially MO and MC, reached both good productivity and provisioning ecosystem services (improving soil quality, carbon sequestration, regulation of pests ). Systems with only timber trees and BO collapsed. The economic analysis shows that most agroforestry systems are profitable, including those with MO or BO, with important lessons to reduce production costs. The most successful innovations related to soil improvements, shade and pest regulation, silvicultural mechanization, and carbon storage derived from the trial, were used as inputs to environment-focus policies, design of researchdevelopment projects and programs such as NAMA coffee. The results have been disseminated to more than 40,000 producers and hundreds of students through projects and relevant platforms such as PCP-AGROFORESTA, PROMECAFE, RECIPROCAFE, the Alianza de Mujeres en Café, PROCAGICA-IICA-UE, and coffee courses/diplomas. Thus, it is being demonstrated that diversification and good practices can contribut

We hypothesized that the nitrogen-fixing tree Acacia mangium could improve the growth and nitrogen nutrition of non-fixing tree species such as Eucalyptus. We measured the N-mineralization and respiration rates of soils sampled from plots covered with Acacia, Eucalyptus or native vegetation at two tropical sites (Itatinga in Brazil and Kissoko in the Congo) in the laboratory. We used a bioassay to assess N bioavailability to eucalypt seedlings grown with and without chemical fertilization for at least 6 months. At each site, Eucalyptus seedling growth and N bioavailability followed the same trends as the N-mineralization rates in soil samples. However, despite lower soil N-mineralization rates under Acacia in the Congo than in Brazil, Eucalyptus seedling growth and N bioavailability were much greater in the Congo, indicating that bioassays in pots are more accurate than N-mineralization rates when predicting the growth of eucalypt seedlings. Hence, in the Congo, planting Acacia mangium could be an attractive option to maintain the growth and N bioavailability of the non-fixing species Eucalyptus while decreasing chemical fertilization. Plant bioassays could help determine if the introduction of N2-fixing trees will improve the growth and mineral nutrition of non-fixing tree species in tropical planted forests.

Past studies showed a gradual expansion of tree cover over savannah in forest-savannah transition zones in Central Africa. While the natural encroachment of savannah by forest is more and more impeded by human activities, farmers in Cameroon have proven that afforestation of savannah is achievable using cocoa and specific technics to build up an associated tree canopy. Furthermore, mature cocoa agroforestry systems created on savannah (S-cAFS) or in forest (F-cAFS) seem to exhibit comparable multi-strata structures. By combining measurements of cocoa yield, litterfall and cycling, soil quality, carbon storage and tree species diversity along an age gradient (1 to 70 years), we showed that those variables in S- and F-cAFS tended to comparable levels after several decades. Results also emphasized the ability of S-cAFS to increase most of the ecosystem services (including soil carbon and nutrients storage) although the time needed to reach levels found in F-cAFS varied strongly amongst variables. We also compared the impact of five associated shade tree species and unshaded conditions on soil functions and cocoa yield in relation to plant functional traits and leaf litterfall within 8 cocoa farms set up after savannah. Unshaded cocoa conditions showed the lowest soil functions associated with the low leaf litter quality of cocoa plants. Soil functions varied largely among species. Low litter recalcitrance was strongly associated with increases in soil N and P availability, while soil pH, soil C and N contents increased with litter Ca restitution. Improvements of soil functions were the lowest under the fruit trees (Canarium schweinfurthii and Dacryodes edulis), intermediate under the legume tree Albizia adianthifolia, and the highest under the timber trees (Milicia excelsa and Ceiba pentandra). We detected no change in cocoa yield between the different treatments because of high variability of data but the P nutritional status of cocoa plants was positively related to

Afforestation of savannah with cocoa agroforestry systems (cAFS) is a common farmer practice in Cameroon previously described as a sustainable production option. Nevertheless, the effects of afforestation of savannah with cAFS on C turnover and content, and the factors controlling C accumulation and stabilization are unknown. Different systems settled on savannah were compared: cropland (≈ 5 years old), cocoa monoculture (≈10 years old) and cAFS (from 20 to 60 years old) shaded by different tree species (Albizia adianthifolia, Canarium schweinfurthii, Dacryodes edulis, Milicia excelsa, Ceiba pentandra). We used savannah and nearby forest patches as controls. Soils were orthic ferralsols with 9-15% of clay content. Soil analysis was performed on the 0-10 cm soil layer for: organic C content, C distribution in soil particle size fractions (0-20 µm, 20-50 µm, and 50-2000 µm), and nutrient contents. Soil delta13C was analysed for studying how the change from savannah grasses (C4 plants) to other vegetation (C3 plants) affected soil C turnover. The amount of annual litter input and its nutrient content were also analysed. Conversion of savannah to cAFS significantly increased soil C to the same level as soil C under nearby forests (Figure 1). Conversion of savannah to annual cropland or cocoa monoculture resulted in a non-significant decrease in soil C. After conversion of savannah to other land uses, more than 70% of soil C derived from C4 plants was lost within 10 years and then remained almost unchanged. Contrastingly, soil C derived from C3 plants increased significantly in cAFS. The C accumulation occurred both in the 50-2000 µm and 0-20 µm soil fractions, and was linked to cumulative higher litter inputs in cAFS than in other systems. Soil C under the different shade tree species was positively linked to soil pH, exch. Ca2+ and litter Ca content. Afforestation of savannah with cAFS appears as a valuable option for soil carbon sequestration.

In Cameroon, cocoa plantations of the Talba pionner front are set up after partial, yet strong, forest clearing and planted with " hybrid " cocoa trees. Previous studies showed complex relationships between preserved forest trees and cocoa yields, which need to be investigated further. In this peculiar cocoa production zone, we studied a chronosequence of 32 cocoa plantations (8 to 73 years old). We measured cocoa and associated trees diameter, height, shade tree cover and cocoa yield. We also estimated basal area and tree biomass. Talba plantations showed a low density of associated trees (32 trees.ha-1) in comparison to other production zones in the country (80 -150 trees.ha-1) and consequently a 35-55% lower carbon storage in aerial biomass (48 Mg.ha-1). The average shade cover was also low (38%) and positively linked to the basal area of associated trees. Associated trees were preserved for timber (Terminalia superba) and/or for their high economic value (Ricinodendron heudelotii). Introduced trees were mainly for self-consumption (Dacryodes edulis). Specific diversity tended to reduce until [40-60] years old. Hence, in the mid-term, these plantations would lose their already low tree species conservation value if farmers were not rapidly encouraged to keep or renew forest-preserved trees. The age of the plot and, to a much lesser extent, the shade tree cover affected negatively cocoa yield. Other canopy attributes did not affect cocoa yield. Cocoa tree density decreased significantly with plot age. The absence of a relationship between the individual cocoa tree and the plot age suggests that the yield decrease with time was mainly due to a lack of renewal of old cocoa trees through coppicing and/or new seedlings planting. The low number of multi-stem cocoa trees in our study area confirms that rejuvenation of old plantations is a challenge for the farmers towards sustainable cocoa production.

La demande de bois augmente partout dans le monde et cette tendance va inévitablement s'accélérer durant le XXIe siècle pour les débouchés traditionnels, mais aussi les secteurs de la construction (36 % des émissions de gaz à effet de serre), de la bioénergie, de la chimie verte et de toutes les industries qui chercheront progressivement à se biosourcer et à se décarboner dans le cadre de l'avènement d'une économie verte durable et relocalisée près de ses ressources et des marchés locaux.

Plus d'un quart de la déforestation (27 %) est provoqué par un changement d'utilisation des terres dû à la production de commodités (Curtis et al. 2018). Les estimations de perte de forêt tropicale attribuées à la progression des cultures, des pâturages et des plantations forestières vont de 62 à 80 % (Pendrill et al. 2019 ; Hosonuma et al. 2012), 26 % de ces pertes étant attribués à la demande internationale de commodités (Pendrill et al. 2019). Partant de cette constatation, on considère que la déforestation est un problème relevant de la responsabilité de la communauté internationale puisque les produits qui en sont à l'origine dans un lieu précis sont vendus et consommés dans le monde entier. On estime que 10 % de la déforestation de la planète sont liés à la consommation, dans les pays membres de l'UE, de commodités importées qui sont produites de façon non durable, la déforestation en Europe étant négligeable (Cuypers et al. 2013).Ce phénomène a donné lieu à deux nouveaux termes : commodités à risque pour les forêts et déforestation due aux commodités. Les commodités liées à la déforestation importée et produites en Afrique centrale sont l'huile de palme, le cacao, le café, le caoutchouc, le bois et le coton.

L'ouvrage présente les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers en zone tropicale. Il concerne, d'une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, d'autre part les parcs arborés et arbustifs à base de cultures vivrières en Afrique de l'Ouest. Il synthétise les dernières avancées autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent.

Plant diversification through crop rotation or agroforestry is a promising way to improve sustainability of agroecosystems. Nonetheless, criteria to select the most suitable plant communities for agroecosystems diversification facing contrasting environmental constraints need to be refined. Here, we compared the impacts of 24 different plant communities on soil fertility across six tropical agroecosystems: either on highly weathered Ferralsols, with strong P limitation, or on partially weathered soils derived from volcanic material, with major N limitation. In each agroecosystem, we tested several plant communities for diversification, as compared to a matching low diversity management for their cropping system. Plant residue restitution, N, P and lignin contents were measured for each plant community. In parallel, the soil under each community was analyzed for organic C and N, inorganic N, Olsen P, soil pH and nematode community composition. Soil potential fertility was assessed with plant bioassays under greenhouse controlled climatic conditions. Overall, plant diversification had a positive effect on soil fertility across all sites, with contrasting effects depending on soil type and legumes presence in the community. Communities with legumes improved soil fertility indicators of volcanic soils, which was demonstrated through significantly higher plant biomass production in the bioassays (+18%) and soil inorganic N (+26%) compared to the low diversity management. Contrastingly, communities without legumes were the most beneficial in Ferralsols, with increases in plant biomass production in the bioassays (+39%), soil Olsen P (+46%), soil C (+26%), and pH (+5%). Piecewise structural equation models with Shipley's test revealed that plant diversification impacts on volcanic soil fertility were related to soil N availability, driven by litter N. Meanwhile, Ferralsols fertility was related to soil P availability, driven by litter P. These findings underline the import

Many studies have shown that introducing N2-fixing trees (e.g. Acacia mangium) in eucalypt plantations can increase soil N availability as a result of biological N2 fixation and faster N cycling. Some studies have also shown improved eucalypt P nutrition. However, the effects of N2-fixing trees on P cycling in tropical soils remain poorly understood and site-dependent. Our study aimed to assess the effects of planting A. mangium trees in areas managed over several decades with eucalypt plantations on soil organic P (Po) forms and low molecular weight organic acids (LMWOAs). Soil samples were collected from two tropical sites, one in Brazil and one in the Congo. Five different treatments were sampled at each site: monospecific acacia, monospecific eucalypt, below acacias in mixed-species, below eucalypts in mixed-species as well as native vegetation. Po forms and LMWOAs were identified in sodium hydroxide soil extracts using ion chromatography and relationships between these data and available P were determined. At both sites, the concentrations of most Po forms and LMWOAs were different between native ecosystems and monospecific eucalypt and acacia plots. Also, patterns of Po and LMWOAs were clearly separated, with glucose-6-P found mainly under acacia and phytate and oxalate mainly under eucalypt. Despite the strongest changes occurred at site with a higher N2 fixation and root development, acacia introduction was able to change the profile of organic P and LMWOAs in <10 years. The variations between available Pi, Po and LMWOA forms showed that P cycling was dominated by different processes at each site, that are rather physicochemical (via Pi desorption after LMWOAs release) at Itatinga and biological (via organic P mineralization) at Kissoko. Specific patterns of Po and LMWOAs forms found in soil sampled under acacia or eucalypt would therefore explain the effect of acacia introduction in both sites.