Développement du cacao au Vanuatu : un bilan contrasté

Troisième exportation agricole du Vanuatu, le cacao est une production surtout villageoise, issue majoritairement de l'île de Malekula. Cultivée principalement en association, la cacaoyère a des rendements modestes dus essentiellement à la faible technicité agricole des planteurs et à l'incidence des maladies et des ravageurs comme la pourriture brune des cabosses et les rongeurs. Des méthodes de fermentation négligées conduisent à un déclin de la qualité : le cacao marchand se classe surtout en grade 2. Pour augmenter la production en volume et en qualité, l'auteur suggère de changer de méthodes de fermentation, de diffuser des clones plus adaptés aux conditions locales et d'apporter plus de soins à la formation des planteurs. (Résumé d'auteur

Evolution de l'agro-biodiversité des systèmes de cacaoculture agro-forestiers du Centre Cameroun

Les systèmes de cacaoculture du Centre Cameroun sont du type agro-forestier. Une étude a été conduite en 2006 dans trois zones de culture du cacaoyer qui ont été différenciées par leur végétation et leurs caractéristiques pédoclimatiques. L'adoption d'une approche synchronique a permis de disposer d'une gamme de cacaoyères représentatives des différents stades de développement du système de cacaoculture. Quinze cacaoyères, réparties en trois classes d'âge (cacaoyères jeunes, cacaoyères adultes et cacaoyères sénescentes) ont été identifiées dans chaque zone d'étude. Les travaux réalisés ont permis d'inventorier les différentes espèces ligneuses associées aux cacaoyers. L'agro-biodiversité des cacaoyères a ensuite été estimée en calculant différents indices. Les résultats montrent que la richesse floristique des cacaoyères du Centre Cameroun varie fortement en fonction de la zone de culture et de l'âge du verger. (Résumé d'auteur

Traditional cacao agroforestry in Central Africa can provide both respectable yields and levels of ecosystem services

Since it moved toward-and tried to apply-intensive production patterns, cacao cultivation in Sub-Saharan Africa represents a major driver of deforestation. In Cameroon, most cacao is still cultivated in low-input traditional agroforests (C AFS). Such systems are still criticised for their presumed low cocoa production and seemingly economic and ecological inefficiency of their associated tree community (ATC). Yet, these household systems proved to be sustainable on the long run and marginally threaten forest land when compared to other producing regions or agricultural systems. We studied a cAFS' 100-year chronosequence and checked for three ecosystem services they provide: (i) cacao production; (ii) carbon (C) storage in tree biomass and (iii) tree species conservation. Within this chronosequence we also studied a large array of associated trees densities (ATD) to better appreciate the role of competition on the services studied. We used, among other variables, basal area (BA) of the different components of the systems to gauge interspecific competition, functional group dynamics and cacao trees productive abilities. Yields were highly depending on the age of the plot, the BA of the ATC and the structure of the cacao stand. Very long-term production seemed achievable if the BA of the cacao stand remained under 40% of CAFS' total BA. High accessible yields underlined a good production potential which was mitigated by interspecific competition. Yet, for a given level of competition some associated functional groups of the ATC were consistently related to higher cacao yields. Furthermore, CAFS were able to combine high levels of tree species richness with long-term conservation abilities and C storage. However, tree species conservation potential depended on ATD and remained difficult to appraise. C storage was highly dependent on large trees and not systematically mitigated by ATD - underlining the possible “uncoupling” of tree species conservation and C sequestration in those systems. ATD reduction emphasised consistent shifts of functional traits / groups that are to alter CAFS functioning and ATC diversity of uses. Thus, a “rough simplification” - as regularly advocated to alleviate the competition between cacao stands and ATC – is mos t likely to impair traditional CAFS ecosystem sustainability. We argue that cacao productivity in these systems can be raised combining consistent rejuvenation and densification practices with site-specific intensification in terms of inputs and/or manpower. Such intensification would not compulsorily include ATD reduction and therefore would, at least partly, facilitate the preservation of some of the ecosystem services supported. (Résumé d'auteur

Matching uses and functional traits of companion trees in cocoa agroforests: a win-win scheme toward resilient systems. [P50]

Africa's cocoa producing countries are currently challenged to design climate-smart cropping models that would satisfy both growers and manufacturers. In this context, Cameroon's cocoa-based agroforestry systems (c-AFS), could serve as a model. Compared with prevailing monoculture systems, these c-AFS significantly support biodiversity conservation and C storage while providing farmers with sustainable low-but-steady cocoa yields. Such a result largely relies on farmers' use of tree diversity since, for example, these c-AFS are not fertilized. We herein check for a putative method helping to better understand the functioning of these very complex systems while including farmers' multiple use of tree diversity. We studied 58 1000m2 c-AFS plots across Central Cameroon. We surveyed farmers' use of companion trees and grouped them in 4 categories: (a) wood- or (b) food production, (c) assumed agronomical support to cocoa growing, (d) other /unknown use. We further checked for 5 functional traits (i) N-fixation, (ii) shade tolerance, (iii) strata, (iv) wood specific gravity; (v) leaf life-span strategy. Out of the 1258 trees recorded, 688 individuals from 50 species could be used to run Multiple Correspondence Analysis (MCA). MCA distinguished between three groups: (1) trees used for their wood appeared to be mainly dominant, of hard wood, and deciduous; (2) pioneer and light wood trees were mainly used to support cocoa growth; (3) food producing trees were mainly evergreen and belonged to the same dominated strata as cocoa. It appears that such clustering helps gauging tree diversity contribution to cocoa yield and shows trades-off or synergies within the system per se as well as between growers' various objectives. Hence, it should help designing/enhancing c-AFS that inherently consider farmers' objectives and local tree species. Furthermore, such method allows climate-smart modelling of c-AFS thanks to the management of ecological functions supported by its tree component. (Texte intégral

Caractérisation et évaluation de systèmes de culture agroforestiers à base de cacaoyers au Cameroun en fonction des conditions environnementales et de la gestion de la fertilité

La région centrale du Cameroun présente un paysage de transition entre forêt et savane. Des pluies irrégulières, des sols de faible qualité, la rareté des terres forestières et des savanes à Imperata sont des contraintes fortes de cette zone sub-optimale pour le cacaoyer. La pression foncière au sein de cette région située à la marge de la zone optimale de culture du cacao conduit les agriculteurs à établir leurs plantations sur savane ce qui représente une alternative surprenante à la pratique traditionnelle d'installation basée sur l'utilisation de la fertilité après déforestation. Les recherches ont été entreprises à la fois sur les pratiques des agriculteurs et les propriétés des sols afin d'évaluer la performance d'un système de culture en fonction de la gestion de la fertilité des sols. Vu les performances de raccourcissement de la période immature et l'accroissement de la teneur en matière organique des sols, les systèmes agroforestiers à base de cacao établis sur savane apparaissent compétitifs et méritent une attention particulière. Cette étude montre des performances de ces systèmes de culture agroforestiers supérieurs dans un environnement de savane que forestiers sans effet dépresseur sur l'agrobiodiversité et la fertilité des sols caractérisée par la teneur en matière organique. (Résumé d'auteur