Mixed effects of agricultural practices and agro-ecological structures on grassland plant diversity.

For a long time, descriptive and experimental studies have shown that agricultural practices affect plant diversity in permanent grasslands. More recently, landscape organization and, more particularly, spatial organization of agroecological structures (AES) was identified as a major factor affecting plant diversity. AES are semi-natural elements, such as hedges, isolated trees, etc. The objective of this study was to evaluate the mixed effects of both agricultural practices and spatial organization of landscape on taxonomic and functional diversity in different French farming systems. We focused on twelve livestock farms distributed along two gradients: i) intensity of agricultural practices, and ii) density of AES on farm territory. In each farm, four types of permanent grasslands were selected in which variables of agricultural practices (date of mowing, livestock rate, fertilization), landscape (AES categories, AES density, AES connectivity) and floristic composition are sampled. Variance partitioning analysis showed that taxonomic diversity is mainly due to landscape variables, like density of hedges and diversity of AES included in a 300 m buffer zone around the floristic survey. The variance of functional indices depended both agricultural practices (livestock and mineral fertilization) and landscape variables such as density of hedges.