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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. [ABSTRACT FROM AUTHOR]

Shea trees (Vitellaria paradoxa Gaertn. f.) have been for perhaps as long as 3000 years probably the most economically and culturally important tree species in Sudanian agroforestry systems. The existing studies show that the specific magnitude and limits of shea tree presence and shea products' advantages are highly variable. This synthesis paper gathers and updates most of the scattered knowledge on shea trees and parklands, reported by category of knowledge: socio-economic potential of shea production, current means of enhancing shea domestication, tree impacts on environmental resources and associated crop production. It concludes with a proposal for a systemic and participative bio-economic modelling approach in order to simulate intensification of shea parklands' production using process-based research results on their economic, agronomic and environmental performance. [ABSTRACT FROM AUTHOR]

Average population growth in the African Sudanian belt is 3 % per year. This leads to a significant increase in cultivated areas at the expense of fallows and forests. For centuries, rural populations have been practicing agroforestry dominated by Vitellaria paradoxa parklands. We wanted to know whether agroforestry can improve local rainfall recycling as well as forest. We compared transpiration and its seasonal variations between Vitellaria paradoxa, the dominant species in fallows, and Isoberlinia doka, the dominant species in dry forests in the Sudanian belt. The fallow and dry forest we studied are located in northwestern Benin, where average annual rainfall is 1200 mm. Sap flow density (SFD) was measured by transient thermal dissipation, from which tree transpiration was deduced. Transpiration of five trees per species was estimated by taking into account the radial profile of SFD. The effect of the species and of the season on transpiration was tested with a generalized linear mixed model. Over the three-year study period, daily transpiration of the agroforestry trees, V. paradoxa (diameters 8-38 cm) ranged between 4.4 and 26.8 L day while that of the forest trees, I. doka, (diameters 20-38 cm) ranged from 9.8 to 92.6 L day. Daily transpiration of V. paradoxa was significantly lower (15 %) in the dry season than in the rainy season, whereas daily transpiration by I. doka was significantly higher (13 %) in the dry season than in the rainy season. Our results indicate that the woody cover of agroforestry systems is less efficient in recycling local rainfall than forest cover, not only due to lower tree density but also to species composition. [ABSTRACT FROM AUTHOR]

Agroforestry systems provide critical benefits for food security and climate change mitigation. Yet, they are complex and heteregoneous sytems hard to optimize. The use of process-based crop models provides an opportunity to understand better the interactions between soil, crop, tree and climate and explore the impact of agroforestry on crop growth, for contrasting crop management. The objectives of this study were to i) calibrate the soil-crop STICS model for pearl millet (Pennisetum glaucum) in order to simulate millet potential growth and impact of water and nitrogen limitations on millet growth in open fields and ii) explore the impacts of the parkland tree Faidherbia albida on millet performance for contrasting N fertilizer inputs. We gathered a comprehensive database of 28 agronomically contrasting situations, ranging from near-potential growth to drought- and N-stress, either on-station or in a farmer's home- or bush-fields. Parameters governing relevant plant and soil processes for grain yield were calibrated in a stepwise procedure. The calibrated model was used to explore the impact on millet growth of the widely reported benefits of Faidherbia albida , namely a minimum reduction in radiation thanks to the peculiar reverse phenology of this tree, improvement of soil water content at the beginning of the growing season and of organic nitrogen in the topsoil. Model simulations with the calibration dataset were reasonably accurate for aboveground biomass and grain yield. Normalized Root Mean Square Errors (nRMSE) for these variables were 29% and 26%, respectively; model efficiency (EF) was 0.58 for both. The nRMSE ranged from 33% to 53% for Soil Water Content (SWC), plant N uptake, grain number, and leaf-area index (LAI). Model accuracy was lower with the evaluation dataset. In the virtual experiment, millet yield decreased with incoming solar radiation, but only at levels of shading (e.g. below 80% of the radiation obtained with full sun) that do not occur under Faidherbia. The decline was greater when millet was fertilized. Increasing the initial soil water content did not affect simulated millet growth. Simulated millet aboveground biomass and grain yield increased with higher organic nitrogen contents of the topsoil, by 80% when millet was not fertilizer, but only by 25% when millet was fertilized. This study provides the first set of comprehensively calibrated parameters for applying STICS to pearl millet in open cropland. A virtual experiment with historical climate suggests that the benefits of Faidherbia decrease if farmers intensify crop production by adding more mineral N fertilizer. Hence, precise fertilizer management is recommended in Faidherbia parklands. These results illustrate the benefits of process-based crop modelling for better understanding the functioning of agroforestry systems. • First calibration of pearl millet for the Stics soil-crop model. • Virtual experiment on the impact of parkland on millet growth. • Millet yield decreased with incoming solar radiation, and more so when millet was fertilized. • Millet yield increased with soil organic nitrogen, but less so when millet was fertilized. • Simulations suggest the decreasing benefits of parkland as farmers intensify crop production. [ABSTRACT FROM AUTHOR]