Mapping plant diversity in cocoa-based agroforestry systems to improve overall productivity

In cocoa-based agroforestry systems (CAFS), the cocoa trees are associated with other cultivated plant species at variable densities. There, the spatial distribution of the cultivated plants can be regular, random or aggregated, and their age may vary even in the same species. Variables of (i) density, (ii) spatial distribution and (iii) age can thus influence the overall productivity of CAFS and its distribution in space. We studied the relationships between these 3 variables and CAFS productivity based on data collected in 34 experimental yield tracking plots placed in agroforestry fields of producers in the Dominican Republic. A mapping of the cultivated plants was carried out on each plot at their installation and harvests of the ripe products of each individual plant were carried out every two weeks over a period of one year. The first results of this study indicate that optimal CAFS productivity can be maintained along a decreasing density gradient of crops, associated with cocoa tree ageing. In addition, regular and random spatial distribution of all plant species may increase overall productivity. The analysis of the variability of cocoa, fruit, tuber and timber yields allows us to provide recommendations on the most suitable species and the optimal distance between plants to improve overall productivity and therefore the producer's income

Compromis entre productivité et biodiversité sur un gradient d'intensité de gestion de systèmes agroforestiers à base de cacaoyers de Talamanca, Costa Rica

Le cacaoyer (Theobroma cacao, L.) est cultivé dans les tropiques humides d'Amérique latine, d'Afrique et d'Asie. Principale source de revenus d'une agriculture essentiellement familiale, les systèmes agroforestiers à base de cacaoyers fournissent de nombreux services écologiques et contribuent à la conservation de la biodiversité. Ces systèmes associent plantes ligneuses et cultures de manière simultanée, dans une gamme importante et peu décrite de richesses et de structures botaniques. Les connaissances actuelles sur leur productivité se limitent à des essais en milieu contrôlé associant un petit nombre d'espèces. Nos travaux testent l'hypothèse d'une relation de compromis entre le niveau de productivité des cacaoyers et le niveau de biodiversité hébergée par les agroforêts à base de cacaoyers. Nous caractérisons ces compromis sur un gradient de situations de production paysannes, reposant sur la structure verticale, l'intensité de gestion de la composante végétale et le contexte bio-physique des agro-systèmes étudiés. Sur un dispositif de 36 cacaoyères paysannes situées dans la région de Talamanca, Costa Rica, nous montrons que des variations significatives de la structure végétale reflètent les modes de gestion de la parcelle et affectent le rendement par cacaoyer (295 à 667g/arbre/an) mais pas le rendement en cacao (136 kg/ha/an), ni le volume végétal global (400 m3/ha). Ces variations de la structure végétale affectent peu la diversité a des peuplements de plantes associées, d'épiphytes, d'amphibiens, de reptiles, de mamifères, d'invertébrés du sol et de la litière, mais leur diversité b répond de manière contrastée à ces variations d'habitat. Les relations de compromis que nous mettons finalement en évidence entre la productivité en cacao marchand à l'hectare ou à l'arbre et les niveaux de biodiversité atteints sont de nature (linéaire, cubique, quadratique) et de tendances (négative, postive) contrastées selon le taxon considéré et remettent en cause les résultats de certains travaux récents. Nos travaux dévoilent également des situations de compromis optimales, offrant des perspectives positives pour l'intensification écologique des systèmes agroforestiers tropicaux.Cacao (Theobroma cacao, L.) is cultivated in the humid tropics of Latin America, Africa and Asia. Cocoa-based agroforestry systems are the main source of income for smallholders' families and provide numerous ecological services and contribute to biodiversity conservation. These systems associate trees with crops simultaneously, in a wide and poorly described range of botanical and structural plant diversity. The current knowledge about their productivity is restricted to controlled trials with a low numer of associated plant species. Our work tests the hypothesis of a trade-off relationship between the level of cocoa productivity and the level of biodiversity hosted in cocoa-based agroforests. We characterize these trade-offs on a gradient of production situations, based on the vertical structure, the management intensity of the vegetal component and the bio-physical context of cocoa-based agroforests. On the base of a 36 on farm cocoa plots network located in Talamanca, Costa Rica, we show that significant variations in the vegetation vertical structure reflect farmer's management strategies and affect the cocoa yield per tree (295 to 667g/tree/year) but neither the cocoa yield per plot (136 kg/ha/year), nor the global plant volume (400 m3/ha). The variations in vegetation structure poorly affected the a-diversity of 7 plant and animal taxa, but their b-diversity gave contrasted and significant responses to habitat variations. Finally, the trade-offs relationships we display between dry cocoa productivity per hectare or per tree and the observed biodiversity levels showed contrasted forms (cubic, quadratic, linear) and tendances (positive, negative) according to the taxa considered and question results from recent publications. Our work also revealed optimal trade-off situations which offer positive prospects for the ecological intensification of tropical agroforestry systems.MONTPELLIER-SupAgro La Gaillarde (341722306) / SudocSudocFranceF