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Description of the subject. In West Africa, particularly in Burkina Faso, the intensification of agroforestry parks is being increasingly advocated as a means of supporting rural populations faced with the steady reduction of trees in their agricultural and pastoral production systems. However, the implementation of these interventions is situated within a social context characterized by a diversity of actors with often divergent interests. Objectives. This study aimed at identifying relevant stakeholders to be included in a reflection process to co-construct agroforestry park intensification scenarios. Method. To that end, a purely qualitative approach was used, combining literature review, stakeholder mapping workshops and semi-directive interviews in the municipalities of Koumbia, Guéguéré and Dano. Results. The results show that in the communes of Koumbia and Dano, the management and use of trees is carried out by a diversity of actors with similar (converging) interests in the intensification of agroforestry parks and interconnected by commercial, information, and knowledge exchanges and power relations. Conclusions. This study made it possible to collectively define the contours of an innovation platform including all actors in each village with a centralized management at the commune level, allowing the co-construction of tree-park intensification.

Description of the subject. We present a literature overview of innovation platform practices in Africa, combined with case studies of sub-national platforms established in Senegal and Burkina Faso. Objectives. The main objective was to understand how the facilitation process of innovation platforms can become more effective. Two specific objectives were to study RAMSES II innovation platform cases in Senegal and Burkina Faso where we observed and reflect on the facilitation of agroforestry innovation platforms. A final objective was to position the case results in a literature overview of IP experiences in Africa. Method. Information on innovation platforms was collected by combining an analysis of RAMSES II agroforestry innovation platform cases and an innovation platform literature review. Results. The study illustrates how the organizational position of the facilitating research agents contributed to shaping platform agendas, functions, and outcomes. This process hinges on the deployment of legitimacy claims, which appeal to technical expertise and scientific narratives, in this case on agroforestry. Institutional embeddedness is shown to be a critical aspect of agency in innovation platform multi-actor processes, contributing to framing local understandings of agroforestry and to channel collective efforts. Conclusions. The institutional identity of facilitating research agents and their relationship to members of a platform requires a more open and process oriented role. Coordination and facilitation roles can also be taken up by other members of the platform. This enhances the platform’s ability to ground their agendas into local needs and priorities. It also enhances sustainability, as active membership during the project period prepares platform members to continue after project closure.

Agroforestry systems in central Senegal, commonly referred as parklands, are mostly composed of Faidherbia albida trees scattered in pearl millet or in groundnut crops. Many studies showed that this Nitrogen-fixing legume tree increased millet production and soil fertility. Most studies consisted of comparing millet yield under and far outside the tree crown of isolated, mature and non-pruned trees. However, how the tree density, tree size and pruning intensity within F.albida parklands may affect the tree services is not known yet. To address this question, a network of 73 contrasted F. albida parklands selected over 5 villages was monitored over the rainy season 2019. The sampled parklands showed various combinations of tree density, tree trunk size and pruning intensity. In each sampled parkland, we set up a pair of plots of 16 m2 on millet crop, one under the canopy of a selected F. albida tree, and the other halfway between this tree and the nearest F.albida tree. Our results showed that millet grain and straw yield, soil organic carbon, N and P Olsen were significantly higher under the tree canopies than halfway between two trees. Multiple Linear Regression Statistics indicated that higher tree density had a significant positive effect on the millet grain yield, and the tree size had a significant positive effect on the soil variables. Unexpectedly, high tree pruning, removing about 60% of the potential tree canopy area, had no significant effect. We concluded that tree density and size may increase F. albida tree services and thus, the millet crop sustainability. Moreover, the current tree pruning intensities allowed farmers benefit simultaneously from direct provisioning services of F. albida trees, and from their indirect services regarding soil fertility and millet yield. These results may help reasoning innovative management practices for these parklands.

Faidherbia albida is a fertilizer and forage woody species of agroforestry systems in semi-arid Africa., It is phreatophyte and shows reverse phenology (leafless in rainy season) what is expected to avoid competition for soil water with associated crops. Moreover, the root access to groundwater is assumed to prevent constraint on transpiration. However, the details of F. albida transpiration and canopy conductance under daily and seasonal conditions are poorly known. The on-farm study was conducted at Faidherbia-Flux station in the population-health-environment observatory of Niakhar, Senegal. Five mature trees were selected in the stand with a density of 6.9 tree ha-1. Sap flow, xylem and soil water content were continuously recorded over a complete year with meteorological variables and measurements of canopy phenology, leaf area index and leaf water potential. Maximal transpiration estimated from sap flow peaked around 210 L tree-1 day-1 in the early dry season (December) for an average tree (DBH of 48.5 cm and 260 m² of leaf area). The transpiration slowly decreased up to June before a sharp decrease following intense defoliation at the beginning of the rainy season in July. Predawn leaf water potential ranged between 0.25 in early dry season and 0.45 MPa in mid dry season, indicating a low water constraint. However, the reference canopy stomatal conductance per leaf area (at 1 kPa of air vapour pressure deficit, VPD) decreased from around 100 in early dry season to 50 mmol m-2s-1 in mid dry season suggesting a significant regulation. Moreover, in both case, the canopy stomatal conductance was highly sensitive to VPD with a 50% decrease at 3 kPa. This study provides new bases for transpiration modeling of Faidherbia albida in agroforestry parklands. It particularly suggests to also consider the influences of soil surface drying and air dryness on transpiration regulation of Faidherbia.

Faidherbia albida agroforestry parklands are widespread in Sub-Saharan Africa under 250-600 mm of annual rainfall. Given its potential to provide a large spectrum of ecosystem services (ES) largely displayed in the literature, F.albida parklands are now widely recognised as a promising option to meet the 2030 UN SDGs. However most evaluations were carried out at the tree scale and a landscape scale assessment of the multiple ES they provide and their interactions is still lacking. Our aim is to provide a first characterization of the spatial supply of multiple ES and their relationships. Our study was conducted in 2019 in the groundnut basin of Senegal. We combined observed data for 11 ES indicators (including provisioning, regulating and supporting/regulating services) from 136 sampling points with remote sensing-derived data. First, the spatial distribution of each ES supply was modelled using machine learning approaches. The ES indicators were modelled with accuracies ranging from 68% to 96%. Results indicated that the majority of ES indicators remained below ES potential values over the study area by 25% to 50% suggesting that there is potential for increasing the ES supply in the F.albida parkland. Second, combining a scoring approach with a spatial co-occurrence method, we identified the dominant relationships among ES and we analyzed their distributions according to the distance from F.albida trees. We showed that losses, synergies and tradeoffs accounted for 41%, 40% and 19% respectively of the dominant relationships. Synergies were predominant between 0-10 m from the trees. Above this threshold, synergies started to decrease as one moved away from the trees while the proportion of losses and trade-offs relationships increased. By providing spatially explicit information on multiple ES relationships, our results can contribute to the development of evidence-based innovative management of agroforestry parklands and, more generally, multifunctional landscapes.

PR, IFPRI3; ISI; CRP2, PIM, CGIAR Research Program on Policies, Institutions, and Markets (PIM), It is more and more acknowledged that agroecological innovations, such as agroforestry practices, should be co-created through a combination of research and traditional knowledge, be context adaptable, and meet the needs of producers and consumers. The word “innovation” recognises that agroforestry practices do exist everywhere in the world. However, to be able to effectively respond to global challenges and changes (demography and social changes, climate, local to international markets), speaking about "innovations" implies that these practices could be improved or transformed or reintroduced everywhere they had disappeared or are in decline. This reality is still current despite the significant number of research and innovation programmes, the volume of mobilized funds and the number of participating organizations. Increasing adoption of agroforestry practices also requires long term planning and coordination because trees’ life cycles are often longer than human life. This special issue includes papers on some agroforestry innovations that merit consideration for scaling up, on successful experiences that answer priorities expressed by stakeholders while taking into account their constraints, and on systemic approaches and frameworks to the development of more comprehensive perspectives on scaling up.

The trees in agroforestry plots create spatial heterogeneity of high interest for adaptation, mitigation, and the provision of ecosystem services. But to what distance, exactly, from the tree? We tested a novel approach, based upon geostatistics and Unmanned Aerial Vehicle (UAV) sensing, to infer the distance at which a single agroforestry tree affects the surrounding under-crop, to map yield, litter (i.e. stover) and compute crop-partial Land Equivalent Ratio (LERcp) at the whole-plot level. In an agro-silvo-pastoral parkland of semi-arid western Africa dominated by the multi-purpose tree Faidherbia albida, we harvested the pearl-millet under-crop at the whole-plot scale (ca. 1 ha) and also in subplot transects, at three distances from the trunks. We observed that the yield was three times higher below the tree crown (135.6 g m−2) than at a distance of five tree-crown radii from the trunk (47.7 g m−2). Through geostatistical analysis of multi-spectral, centimetric-resolution images obtained from an UAV overflight of the entire plot, we determined that the 'Range' parameter of the semi-variogram (assumed to be the distance of influence of the trees on the Normalized difference vegetation index (NDVI)) was 17 m. We correlated the yield (r2 = 0.41; RRMSE = 48 %) and litter production (r2 = 0.46; RRMSE = 35 %) in subplots with NDVI, and generated yield and litter maps at the whole-plot scale. The measured whole-plot yield (0.73 t ha-1) differed from the one estimated via the UAV mapping by only 20 %, thereby validating the overall approach. The litter was estimated similarly at 1.05 tC ha-1 yr-1 and mapped. Using a geostatistical proxy for the sole crop, LERcp was estimated 1.16, despite the low tree density. This new method to handle heterogeneity in agroforestry systems is a first application. We also propose strategies for extension to the landscape level.

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.

The adaptation of semi-arid crops to climate changes is theoretically possible through agroforestry, provided that the trees exert little competition, or even increase the multifunctional LER (LER_M). We monitored microclimate, net primary productivity (NPP), CO2 and H2O fluxes in a semiarid agro-sylvo-pastoral system (Niakhar, Senegal), dominated by the multipurpose Faidherbia albida (FA) tree. Undercrops were mainly millet and peanut, under annual rotation. We scanned a 1.24 ha millet under FA plot with UAV photogrammetry in RGB, thermal infrared and multispectral bands. At harvest, we collected 12 subplots of 15 millet holes each, distributed either below the crown of FA, or at 2.5 x crown radius, or at 5 x crown radius. We separated all organs. The whole millet root system (0-200 cm) was sampled also in 2 m trenches, totalizing 4 millet holes, where all roots were sorted by layer. The whole plot harvest will allow extrapolating yield from subplots, through UAV images. Millet yield per unit ground area was about 3 times higher below FA, with still a positive influence at 2.5 x crown radius and less impacts of pests close to FA. In the trenches, we noted higher soil humidity and SOC close to the FA trunks. This observatory is open for collaboration.