| Summary: | Les pertes de récolte dues aux ravageurs et aux maladies constituent une menace sérieuse pour les revenus et la sécurité alimentaire de milliers de familles rurales dans le monde entier. L'évaluation de ces pertes de récolte (baisse de rendement et préjudice économique) et de leurs causes est nécessaire pour améliorer la mise au point d'agroécosystèmes capables d'offrir de bons rendements de culture, une régulation des ravageurs et des maladies et d'autres services écosystémiques. Ce mémoire de doctorat vise à contribuer à la recherche dans le domaine des pertes de récolte en proposant des approches expérimentales et de modélisation susceptibles d'être utilisées pour estimer les pertes primaires et secondaires subies dans les cultures pérennes, et analyser leurs causes. La culture pérenne étudiée est celle du caféier à Turrialba au Costa Rica, où la culture du café se pratique dans des plantations qui vont de la monoculture à pleine exposition solaire à des systèmes agroforestiers hautement diversifiés, et qui sont soumises à une gamme de situations de production (topolimat, fertilité du sol, types d'ombrage) et de stratégies de gestion (pratiques culturales et intrants). Les trois questions de recherche principales ont été les suivantes : Quel est l'impact des stratégies de gestion et des situations de production sur les ravageurs et les maladies et les rendements en café ? Comment les pertes de rendement en café associées à des profils de dégâts donnés varient-elles en fonction des stratégies de gestion et des situations de production ? Quels types d'agro-écosystèmes à base de caféiers permettent de minimiser les pertes en café (baisse de rendement et préjudice économique) et de maximiser les avantages globaux retirés (services écosystémiques) ? === Crop losses due to pests and diseases are a major threat to incomes and food security of thousands of rural families worldwide. The assessment of crop losses (yield and economic losses) and their causes is needed to improve the development of agroecosystems capable to offer good crop yields, regulation of pests and diseases, and other ecosystem services. This doctoral research aimed to contribute to the research field of crop losses, by providing experimental and modeling approaches that could be used in perennial crops to estimate primary and secondary losses and analyze their causes. We worked in a perennial crop such as coffee, in Turrialba, Costa Rica, where coffee is grown in plantations from monocultures at full sun exposure to highly diversified agroforestry systems, and under a range of production situations (topoclimate, soil fertility, types of shade) and management strategies (agricultural practices and inputs). The three main research questions were: What is the impact of management strategies and production situations on pests and diseases and coffee yields? How do coffee yield losses caused by injury profiles vary in function of management strategies and production situations? Which types of coffee agroecosystems are capable to obtain the lowest coffee losses (yield and economic) and highest overall benefits (ecosystem services)? This research was developed through two experimental designs. The first was an experimental coffee parcel under controlled conditions (three-year experiment) to quantify primary and secondary yield losses by comparison of treatments, and to identify the main predictors of yield losses by structural equation modeling. The second experimental design was based on surveys in a coffee research plot network (coffee plots of smallholder farmers), where, during two years, we measured indicators of yields and indicators of four ecosystem services: regulation of pests and diseases, provisioning of agroforestry products, maintenance of soil fertility, and carbon sequestration. Yield losses in this network were estimated through modeling using the predictors identified in the experimental coffee parcel. Analyses of data included several statistical techniques, from analysis of variances, linear regressions to multivariate techniques. The results were organized in four manuscripts, and then discussed integrally. The main findings were: i) Both production situations and management strategies determine coffee yield and pest and disease injuries, effects of interactions altitude x management x types of shade must be considered; ii) Injury profiles depend on particular combinations of production situations and management strategies, with impacts on yield losses especially in a year of high coffee production (primary yield losses), but compromising also the yields of the next year (secondary yield losses); iii) Diversified agroforestry systems have better chances to regulate pests and diseases (reduce yield and economic losses), and simultaneously provide goods for family benefits, maintain soil fertility, and increase carbon sequestration, without implying trade-offs among these ecosystem services. The main prospects of this research are related to perform similar studies in coffee and other perennials at regional levels, develop an injury profile simulator for coffee, and prototyping of coffee agroforestry systems to optimize the provision of multiple ecosystem services.
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