The influence of farming on weed flora in the Gäu region of Southwestern Germany with an emphasis on rare arable weed species

Highly developed weed control strategies manage to suppress weeds and therefore contribute to a shift in weed community composition as well as a decline in rare weed occurrence. To counteract this decline fields containing rare weed species are taken under contract for preservation purposes, however only time limited. We mapped the weed flora in cereals of conventional (K) and organic (O) fields as well as current (V) and former (E) rare species conservation fields in the Gäu region of Southwestern Germany in 2016. We found similar weed species numbers in O (24 – 38 species) and V (36 – 43 species) and in C (7 – 17 species) and E (13 – 15 species). Weed community composition varied considerably between fields. By performing a CCA (Canonical Correspondence Analysis) we were able to explain 23% of the weed community composition by the parameters seeding rate and nitrogen fertilization. Nevertheless species such as Alopecurus myosuroides, Geranium dissectum, Papaver rhoeas, Poa trivialis and Veronica persica showed a high consistency in all observations. Rare and endangered weed species like Papaver argemone, Consolida regalis, Ranunculus arvensis and Galium tricornutum were only present in V and occasionally E and O. This indicates a rapid decline of weed species diversity after contracts expire, which slowly leads to a similar floral composition as in conventional fields. Therefore new concepts for constant protection of rare weed species should be put into action to ensure conservation success.