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Abstract
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.