Genetic diversity of agricultural crops in Flanders over the last five decades

In this study, we describe the evolution of crop diversity in Flanders, using three indicators to measure diversity between crops and within crops: the Shannon index (H), the evenness index (E) - both used for diversity between and within crops - and genetic relatedness between varieties (CP). Despite the significant increase in the number of crops in Flanders, from 67 in 1950 to 101 in 2002, the results show a weak decrease in crop diversity between 1950 and 2002: H decreased from 2.52 to 2.50 and E decreased from 0.58 to 0.53. This apparent contradiction can be explained by the fact that the 'new' crops are mainly vegetables, which only have a small share in the total agricultural area, and thus hardly influence the overall crop diversity. The evolution of genetic diversity between varieties (within crops) from 1980 to 2002 is crop-specific. For maize, the number of cultivars with a high CP (>= 0.125) increased from 1.8 to 7.5%, indicating a decrease in genetic diversity. For potato and winter wheat the number of cultivars with CP >= 0.125 decreased (from 7.3 to 3.7% and from 6.9 to 6.0%, respectively), indicating an increase in genetic diversity within these crops, which is confirmed by the increase in the crops' H and E values.