Biophysical interactions between shade trees and coffee in Central American agroforestry systems
With the financial assistance of the European Union (ICA4-CT-2001-10071), research has been undertaken for the last 3 years on coffee and tree associations in Central America (www.casca-project.com). Its purpose is to promote coffee agroforestry systems in the region and to improve farmer's income through diversification (timber production), production of high quality coffee and payment of incentives for environmental services in order to compensate the current low coffee prices. Intensive measurements have been undertaken to model light and water partitioning between coffee and trees. The impact of shade trees on microclimate, coffee physiology and quality has also been investigated. Especially under sub-optimal conditions, the results show that tree shade creates more favorable microdimatic conditions for coffee and improves coffee photosynthesis. They demonstrate that coffee transpiration is lower under tree shade (Eucalyptus deglupta or Terminalia ivorensis) than in full sun. Nevertheless, they indicate that water competition can take place during the last weeks of the dry season. These results demonstrate that adequate shade (20-40%) decreases coffee productivity by 15-25%. However, this lower productivity can be financially compensated by an increased proportion of larger beans suitable for export and the premium paid for higher cup quality. Indeed, shade lengthens by up to 6 weeks the maturation of coffee berries resulting in better bean filling and beverage quality. These investigations indicate that modelling the effects of agroforestry practices on microclimate, resource partitioning, coffee physiology, productivity and quality is required to provide adequate recommendations for selecting and managing associated trees according to local ecological conditions. (Texte intégral)