Seed dispersal by mowing machinery in a Dutch brook valley system

Seed dispersal by mowing machinery was investigated within a grassland reserve. Transported seed numbers amounted to hundreds of thousands. Seeds of 26 species were found on the machinery, including species that play an important role in succession during vegetation restoration (Holcus lanatus, Rhinanthus angustifolius, Anthoxanthum odoratum). Species occurrence was related to field abundance, but not to plant size, seed size or month of first flowering. Species seed amounts were also positively correlated only to their abundance within fields. Several abundant species were not found because they carried no seeds at the cutting date (Caltha palustris, Juncus acutiflorus). There was a difference in species composition within material accumulating in two machinery parts, which was related to their height above ground level. It was concluded that dispersal by mowing machinery is moderately selective towards and against certain species. Seeds were transported from species-rich fields into species-poor fields and vice versa. The seeds transported after mowing a field were partially deposited in the next field. Dispersal by machinery may have a larger impact on the speed of succession in the hay-fields of the Drentse A reserve than any other form of dispersal and establishment from the seed bank. Therefore, it is important for vegetation restoration in practice. However, machinery does not always connect seed sources with restoration areas. Large-scale machinery movement also creates a new form of vegetation dynamics compared to the days of former, more primitive, agricultural use. Both factors have to be considered when attempts are made to restore species-rich vegetation types. It is probable that new methods will not produce the vegetation that once existed.