Agrobiodiversity of Field Crops: A Case Study for Iran

Agrobiodiversity of field crops in Iran was studied at the cropping system, crop species, and crop variety levels using the data collected from 183 counties in 27 provinces. Two wheat-based and rice-based cropping systems were studied. While the rice-based system is limited to a narrow strip of land adjacent to the Caspian Sea, the wheat-based system is dominant in other parts of the country. The cropping intensity index (CII) of the whole country was 0.74, with higher values in the Caspian Sea basin and lowest values in the central and southern regions. Crop rotation indices (CRI) and crop rotation diversity indices (CRDI) were low in all provinces, indicating that crop rotation was either not practiced or was done using very short-sequenced rotations. The Shannon index for crop species diversity was low, ranging between 0.8 and 1.97, with the highest and the lowest values for forage crops and cereals, respectively. α-and β-diversity, estimated from species-area curves, varied considerably between provinces, depending on their climatic homogeneity. The Margalef index for varietal richness varied from 1.7 for rice to 0.3 for rainfed wheat. In general, 25% to 30% of the total varieties accounted for 70% to 85% of the total cultivated area of each crop. Intensive use of a limited number of varieties has led to strong inter-provincial similarity among the main crop species.