Using Economics to Explain Spatial Diversity in a Wheat Crop: Examples from Australia and China
Spatial diversity indicators may serve an important function for policymakers as they seek to manage crop genetic diversity and potential externalities associated with diffusion of some types of genetically improved crops. This paper adapts spatial diversity indices employed by ecologists in the study of species diversity to area distributions of modern wheat varieties in contrasting production systems of Australia and China. The variation in three interrelated concepts of diversity "richness, abundance, and evenness" is explained by factors related to the demand and supply of varieties, agroecology, and policies using the econometric method of Zellner's seemingly unrelated regression (SUR). Results suggest that in addition to expected yield and profitability, other variety characteristics are important in explaining variation in the spatial distribution of modern wheat varieties. Environmental factors and policy variables related to the supply of varieties, international research spillins, and market liberalization are also determinants of the diversity in these systems. Explanatory factors affect richness, abundance and evenness in the distribution of modern wheat varieties in different ways. Comparing results between a small, commercial wheat-producing shire in Australia and a large, heterogeneous area in seven provinces of China illustrates the importance of scale and the nature of the farming system. Further research might include: (1) refinement of methods used to construct spatial diversity indices by incorporating geographically-referenced information; (2) more explicit treatment of the relationship between scale of measurement and diversity indices; (3) refinements in the specification of policy variables, and (4) application of similar methods in zones where traditional varieties are grown.
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