The dissertation consists of 3 essays. In the first essay, a formal model is developed simulating the emergence of a dual economy of nomads and farmers. Given the characterization of risk in a spatio-temporal framework, adaptive strategies of pastoralists perform at least as well as non-adaptive strategies irrespective of risk preference. While the spatially non-adaptive production technique of the farmer is associated with exclusive property rights, the spatio-temporally adaptive strategy of the nomadic pastoralist induces property rights which are non-exclusive. Policy implications of the model are suggested for the agro-pastoral production system of the Sahel. The second essay deals with usufructuary property rights systems developed by farmers, in the semi-arid tropics of West Africa, which provide the farmer with security over income streams derived from the investment of labour and capital in land. The application of the usufruct principle to income derived from irreversible techniques induces relatively permanent usufruct. However, the adoption of an irreversible technology produces a negative externality since the flexibility of the common property regime is reduced. Environmental uncertainty and land scarcity are among the major factors determining the cost of this externality. Empirical applications and policy implications are outlined. The third essay analyses local credit markets in the grassfields of Cameroon. Transactions costs of credit contracts are reduced by the institutional design of rotating savings and credit associations. The relationship between unconditional explicit contracting for credit and conditional implicit contracting for insurance is outlined within a context of temporal liquidity preferences. In the conclusion, a parallel is drawn between the optimality of adaptive strategies in the empirical context of West Africa and the optimality of government policies which stress a process-approach to economic development. (CAB Abstract)