Abstract
Growing crops or pastures in intimate combination with trees is an ancient practice that farmers have been using throughout the world. Globally, it is estimated that agroforestry systems cover about 1 billion hectare of land (Zomer et al. 2014, 2016). Agroforestry systems are often seen by farmers and practitioners as a way to diversify production, income and services (Abdulai et al. 2018). These systems are still very common in developing countries. In developed countries where the intensification and specialization of agriculture have resulted in a massive loss of tree cover (Eichhorn et al. 2006) and in negative impacts on the environment (Tilman et al. 2001), agroforestry systems are currently being reconsidered and spreading (den Herder et al. 2017). Agroforestry systems include a diversity of practices ranging from complex associations found in homegardens, multistrata systems or agroforests, to simpler systems such as alley crops, riparian plantings, shelterbelts, windbreaks or hedgerows (Nair 1985). The association between trees and crops or pastures can be simultaneous (spatial interaction) or sequential (temporal interaction) (Somarriba 1992; Torquebiau 2000).