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Until recently, the health of cultivated plants has been approached through "pathogenic" approaches, focusing on chemical control methods against pests. To accelerate the agroecological transition, a paradigm shift is required with "salutogenic" approaches (Döring et al., 2012). These new approaches aim to better understand the natural mechanisms of pest regulation, in order to maintain plant health without using chemical products. Within cocoa-based agroforestry systems (AFS), there is a wide gradient of agrobiodiversity varying in terms of species diversity, planting density, and spatial distribution of plants (Vroh et al., 2019). Moreover, these AFS are managed by farmers who implement distinct farming practices based on knowledge and beliefs rooted in cultural, academic, and experiential heritage (Toffolini et al., 2016). This agrobiodiversity and agricultural management interact with the health of cocoa trees. We hypothesize that there are statistical correlations between farming practices, agrobiodiversity characteristics and cocoa tree health.
To test our hypothesis, we studied 38 AFS in the Agnéby-Tiassa region of Côte d'Ivoire, selected according to gradients of agrobiodiversity and intensity of farming practices. Half of the sample was conducted in organic farming, necessary to assess the effectiveness of natural pest regulations. The other half was conducted in conventional agriculture, which is the predominant management mode for Ivorian cocoa production. To characterize the agrobiodiversity associated with cocoa trees, we conducted botanical inventories, dendrometric monitoring, and mapping. This agrobiodiversity was then studied in two components: (i) plant composition, corresponding to the abundance of each associated crop species, and (ii) structure, including the variables of height stratum, basal area (m² ha-1), species richness, planting density (plant number ha-1) and spatial distribution (aggregated, random or regular). In addition, semi-structured interviews with farmers allowed us to characterize agricultural practices related to cocoa tree health, evaluate their perception of cocoa tree health, and map zones where cocoa trees are considered to be in "good health" (GH) and "poor health" (PH) according to their criteria. We created typologies of practices and associated agrobiodiversity (plant composition and structure) at the plot and zone levels through multivariate statistical analyses. We tested the relationships between these typologies with the management mode (organic vs conventional) at the plot level, and with cocoa health at the zone level, using Fisher's test.
Our results reveal that at plot level, although the inputs used are often different, organic farmers have a similar intensity of plot management to conventional farmers. There is a statistically significant correlation (p-value=0.05) between the associated agrobiodiversity structure and the management mode. Organic plots are distinguished by a higher specific richness of associated plants than conventional plots (26 compared to 17), also a larger basal area (10.2 m² ha-1 compared to 6.4 m² ha-1) and a higher average stratum (2.01 compared to 1.54).At the zone level, an almost statistically significant correlation is observed between agrobiodiversity structure and zone health, only for plots that are managed with organic farming (p-value=0.07). In these plots, GH zones are distinguished from PH zones by their specific richness with 11.0 vs 6.8.
Only structural characteristics of agrobiodiversity distinguish organic vs conventional plots: the trees associated in organic plots are taller and wider, and are represented by a greater diversity of species. By maintaining this structure, organic farmers certainly expect more services from agrobiodiversity than conventional farmers. In organic plots, the results at the health zone scale suggest that biological regulation depends on the specific richness of agrobiodiversity. The combination of results obtained at plot and health zone scales suggests that the structure of agrobiodiversity, including species richness, and not plant composition, has a positive impact on the biological regulations that can operate to maintain healthy cocoa trees. They open up new research perspectives to better understand the biotic and abiotic regulations that explain the better health of cocoa trees in GH zones compared to PH zones in organic agriculture. Regular quarterly assessment of the agroecological functioning of these health zones through measurements of the cocoa trees, the soil and the microclimate, associated with an assessment of agricultural practices using activity analysis methods, will help to better understand the links between practices, environment, and cocoa tree health, and thus contribute to identifying and designing more agroecological practices.
| Keywords | Cocoa tree; Plant health; Agroforestry system; Salutogenic; |
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