Agricultural intensification degrades arable weed diversity into phylogenetically unstructured subsets of tolerant species

Abstract Context The rise of agricultural intensification (AgI) has severely impacted arable weeds, making it crucial to understand how this process shapes their assemblages across agricultural landscapes. Objectives To elucidate how variation in species composition (beta diversity) among arable weed assemblages respond to AgI gradients, with a particular focus on whether phylogenetic relationships structure these patterns. Methods We analyzed farm-level arable weed assemblages across nine European regions with distinct agricultural management contexts, focusing on in-field AgI indicators (yield, nitrogen fertilizer, pesticides) and landscape context (field size, cultivated area, crop diversity). To examine compositional changes among assemblages, we partitioned beta diversity into its turnover and nestedness components. Results We found positive correlations between in-field AgI differences among farms and the nestedness component of taxonomic beta diversity, alongside a previously reported negative relationship between in-field AgI and species richness. In contrast, the landscape dimension of AgI had a comparatively minor effect. Phylogenetic structure metrics showed weak and inconsistent responses to AgI. Conclusions In-field variation in AgI—rather than landscape context—contributes significantly to taxonomic dissimilarity among arable weed assemblages on European farms, with increasing AgI driving the exclusion of sensitive species and the persistence of tolerant ones, without evidence of species potentially restricted to highly intensified conditions. Traits associated with AgI likely evolved through distinct and complex evolutionary trajectories long before the surge of AgI in the mid-twentieth century, which may explain the phylogenetically unstructured patterns observed.