Weed Diversity, Phytosociological Structure and Co-occurrence Patterns in Cereal Fields of the Sétif High Plateaus (Algeria)

Weeds constitute a major biotic constraint in rainfed cereal agroecosystems of semi-arid regions, where limited and irregular rainfall intensifies competition for water and nutrients. This study investigated weed diversity, phytosociological structure, and co-occurrence patterns in cereal fields of the Sétif High Plateaus (northeastern Algeria) based on repeated field surveys conducted over three consecutive growing seasons (2021/2022-2023/2024). A total of 353 quadrats (1 × 1 m) were sampled across 118 cereal fields covering 35 cereal-producing areas. Phytosociological parameters, including frequency, density, abundance, and the importance value index (IVI), were calculated for each species, and dominant weeds were identified using Two-Step cluster analysis. Weed assemblage organization was further examined using co-occurrence network analysis. The survey recorded 192 weed species belonging to 29 botanical families, dominated by Asteraceae, Fabaceae, and Poaceae, with annual species largely prevailing, reflecting adaptation to recurrent disturbance and semi-arid conditions. Marked differences in dominance patterns were observed among key weeds. Sinapis arvensis was highly frequent and widely distributed but showed moderate local abundance, Bromus rigidus exhibited high density and the highest Importance Value Index (IVI), reflecting its strong competitive dominance in the community. In contrast, Avena sterilis was less frequent but locally very abundant, forming dense and spatially heterogeneous infestations. Co-occurrence analysis revealed non-random weed assemblages, with S. arvensis and Silybum marianum displaying strong and recurrent associations. These findings highlight the importance of targeting weed communities rather than individual species and support integrated weed management strategies adapted to dryland cereal systems of northeastern Algeria.