Sub-Saharan African economies depend heavily on agriculture. Seed from improved varieties and other inputs are imperative to the transformation of the agricultural sector from subsistence farming to small-scale commercial agriculture and thus to increasing food security on the continent. Farmers make the decision to adopt seed from improved varieties based on a number of seed attributes. These range from tangible attributes such as input costs and yield to intangible attributes such as trust in seed from improved varieties. In the course of adoption decisions, social dynamics involving trust can over-ride objective evaluations of tangible attributes. This makes it difficult to design sustainable adoption policies in an intuitive way. For this purpose, we develop a system dynamics model and combine it with conjoint analysis. Conjoint analysis allows us to elicit smallholder farmers' choice preferences in detail and to add precision to the structure of the model. The simulation framework helps to improve our understanding concerning the dynamic implications of accumulation processes relating to trust and skill. We test this approach with empirical data for maize in Malawi. Model simulations demonstrate that effective adoption stimulation policies should focus on measures that build trust in improved maize varieties instead of increasing their potential yield even further and, in this way, contribute to food security.

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Tropical tree plantations may play an important role in mitigating CO 2 emissions through their potential to capture and sequester carbon from the atmosphere. The Clean Development Mechanism (CDM) as well as voluntary initiatives provide economic incentives for afforestation and reforestation efforts through the generation and sale of carbon credits. The objectives of our study were to measure the carbon (C) storage potential of 1, 2 and 10-years old Tectona grandis plantations in the province of Chiriquí, Western Panama and to calculate the monetary value of aboveground C storage if sold as Certified Emission Reduction (CER) carbon credits. The average aboveground C storage ranged from 2.9 Mg C ha -1 in the 1-year-old plantations to 40.7 Mg C ha -1 in the 10-year-old plantations. Using regression analysis we estimated the potential aboveground C storage of the teak plantation over a 20 year rotation period. The CO 2 -storage over this period amounted to 191.1 Mg CO 2 ha -1 . The discounted revenues that could be obtained by issuance of carbon credits during a 20 year rotation period were about US$460 for temporary CER and US$560 for long-term CER, and thus, contribute to a minor extent (1%) to overall revenues, only.

The complexity of development processes makes it difficult to observe and interpret the impacts of policies. The authors demonstrate the use and benefits of system dynamics modelling (SDM) in impact evaluation of private sector development programmes. A system dynamics model was hereby specifically used to compare the observed post-intervention situation with a hypothetical non-intervention scenario. They used the model to construct an optimal mix of interventions that supports sustainable private sector development. They found that developing a system dynamics model and 'gaming' with it is an appropriate means to link the behaviour of the industrial system we observe to its structural elements. This supports the understanding of the impact of complex interventions in industrial systems and can be further useful to convey lessons learned from the evaluations of complex systemic interventions.