Vincent de Leijster

17 General introduction 1 agricultural systems (IAASTD, 2009). It defines sustainability as a highly productive system that uses natural resources efficiently while maintaining and enhancing cultural and biological heritage. According to the IAASTD, highly productive but unsustainable conventional agricultural systems could transition towards highly productivity sustainable agroecosystems by implementing improved practices. In addition to many other interventions, it proposes best management practices, soil conservation practices, and diversification to improve the sustainability aspects of the food system. The IAASTD suggests that during the transition phase, productivity is expected to be temporarily reduced, but that it will recover once the newly established sustainable agroecosystem has matured. Inspired by the IAASTD model, I propose an adjusted model for agroecological management transitions on a farm-scale (Figure 1-2). The transition model assumes that agroecological interventions will improve ecological performance, and there is abundant evidence for this (see Section 1.1). There are, however, still gaps in the knowledge of the development trajectories of ecological performance. In Section 1.3 it was determined that these trajectories follow different linear or non-linear shapes, depending on the specific ecological process as well as on the biotic and abiotic conditions. However, there is insufficient evidence regarding the impact of agroecological transitions on economic performance; in Figure 1-2 this is visualized as the dashed yellow area. The economic outcome is uncertain, not only because it may be influenced by external economic incentives, but also because there is a lack of consensus regarding the impact of agroecological practices on internal economic components. Based on these uncertainties I have defined the following four trajectory scenarios: (1) the agroecological transition improves both ecological and economic performance, (2) it improves ecological performancewhereas economicperformance remains unchanged, (3) it improves ecological performance and economic performance is reduced at first, but then recovers to similar values, and (4) it improves ecological performance but leads to lower economic performance.