A novel index of land use intensity for organic and conventional farming of Mediterranean cereal fields

The conservation of biodiversity in agro-ecosystems is closely related to land use. Intensive land use is considered to be a major cause of biodiversity loss. Most studies addressing the effect of land use intensity on biodiversity have compared organic and conventional systems. However, little is known about the heterogeneity of the management intensity within each farming system. We hypothesise that there is a gradient of land use between and within the farming systems and that an index of management intensity is more useful than the farming system for evaluating the effects of the management practices on weed flora. In this study, 18 pairs of organic and conventional cereal fields were selected in northeastern Spain. The farmers were interviewed to gather information on the management practices performed. We selected the five following variables from these interviews: nitrogen inputs, crop diversity, weed control, seed origin and cereal ratio. We used principal components analysis to create a new management index. Weed species richness was recorded in 10 field pairs before crop harvest. Our results showed that the index values displayed huge variation within each farming system. Index values of conventional fields varied between −0.01 and 1.00, whereas within organic ones the values ranged from −1.19 to 0.18. The index better explained weed species richness than did the farming system. The index values demonstrate the existence of a land use intensity gradient, which indicates that it is an over-simplification to always equate organic farming with low intensity management. Here, we also prove that this new index is more appropriate for evaluating the effects of management practices on weed species richness than the classical organic-conventional dichotomy.