During the past decades, agro‐biodiversity has markedly declined and some species are close to extinction in large parts of Europe. Reintroduction of rare arable plant species in suitable habitats could counteract this negative trend. The study investigates optimal sowing rates of three endangered species (Legousia speculum‐veneris (L.) Chaix, Consolida regalis Gray, and Lithospermum arvense L.), in terms of establishment success, seed production, and crop yield losses.A field experiment with partial additive design was performed in an organically managed winter rye stand with study species added in ten sowing rates of 5–10,000 seeds m−2. They were sown as a single species or as a three‐species mixture (pure vs. mixed sowing) and with vs. without removal of spontaneous weeds. Winter rye was sown at a fixed rate of 350 grains m−2. Performance of the study species was assessed as plant establishment and seed production. Crop response was determined as grain yield.Plant numbers and seed production were significantly affected by the sowing rate, but not by sowing type (pure vs. mixed sowing of the three study species), and weed removal. All rare arable plant species established and reproduced at sowing rates >25 seeds m−2, with best performance of L. speculum‐veneris. Negative density effects occurred to some extent for plant establishment and more markedly for seed production.The impact of the three study species on crop yield followed sigmoidal functions. Depending on the species, a yield loss of 10% occurred at >100 seeds m−2. Synthesis and applications: The study shows that reintroduction of rare arable plants by seed transfer is a suitable method to establish them on extensively managed fields, for example, in organic farms with low nutrient level and without mechanical weed control. Sowing rates of 100 seeds m−2 for C. regalis and L. arvense, and 50 seeds m−2 for L. speculum‐veneris are recommended, to achieve successful establishment with negligible crop yield losses.

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Diversity of arable plants in Europe has markedly declined during the past decades and many species have become threatened. Low‐intensity farming can offer potential retreats for these species, while spontaneous dispersal between such fields is unlikely. Thus, reintroduction of endangered species is necessary to restore agrobiodiversity. To test the applicability under real farm conditions, we seeded a mixture of three winter annuals (Legousia speculum‐veneris, Consolida regalis, Lithospermum arvense) at 850 seeds/m2 on four organic farms near Munich, Germany, in autumn 2011. Seed production and soil seed banks were investigated on four plots within one field on each farm for 3 years. In addition, we evaluated seed dispersal caused by arable management along the main machining direction. In the first year, winter cereals were cultivated and the study species emerged at all sites with a seed production mostly exceeding the initial sowing rates. In the third year, species establishment varied depending on crop rotations. Seed production of L. speculum‐veneris was higher than in the two other species, and exceeded the number of originally sown seeds up to 20 times. While L. speculum‐veneris became very common in the seed bank, C. regalis was less abundant and L. arvense hardly developed a soil seed bank. Seeds of L. speculum‐veneris and L. arvense were found up to 15 m and seeds of C. regalis up to 13 m away from the sown plots. We suggest using seed production, seed bank, and dispersal as key indicators to evaluate establishment of reintroduced arable plants.

Agri-environmental schemes involving organic farming or set-aside management aim at promoting biodiversity and restoring ecosystem functioning in agrarian landscapes. Application of pesticides in these crop fields is strongly regulated facilitating the spread of weeds but also allowing for the establishment of endangered herbs and a variety of animals. Recent studies found gastropods and earthworms to be legitimate dispersers of seeds of wild plants. We assumed that both groups also play a significant role in the spread and establishment of wild plants within crop fields. Therefore, we are conducting a series of experiments in three different study systems on (1) the role of earthworms and gastropods as dispersers of rare herbs and weeds in an organic rye field in Germany, (2) the seed feeding behavior of gastropods of plants sown in fallow ground in Switzerland, and (3) weed dispersal in irrigated rice fields by golden apple snails in the Philippines.