Seed availability and gap size influence seedling emergence of dandelion (Taraxacum officinale) in grasslands

Dandelion ( Taraxacum officinale agg.) seedlings colonize gaps in agricultural grassland and give rise to weedy pastures. It was investigated how this colonization is affected by seed availability and gap size. Flowering, seed production and spontaneous seedling emergence in artificial gaps were recorded at seven grassland sites. Fifteen to 126 flowers m⁻² (2·2–18·6 thousands of seeds m⁻²) were produced at particular sites in May 2005. Seed availability explained 0·91 of the between-site variation in seedling abundance. Seedling populations represented c. 0·03 of the seed produced at these sites. Shading, pH, soil nutrients and soil texture did not affect seedling emergence. In 2006, seed was sown at one site in small (33 cm²) and large (400 cm²) gaps on eight occassions during the growing season. Time to germination was on average 10 d shorter and 0·20 more of the seed germinated in small than large gaps, and both varied significantly with date of sowing. Germination was not limited by low temperature. Predation of seeds may have decreased the density of established seedlings. Patches of dandelions in sparse or weakly disturbed grassland are unlikely to disappear spontaneously and repeated cutting during spring flowering is recommended as an effective means of management.