Question: Which one of the two mainly used mowing regimes along road verges, mowing once or twice a year is a better option regarding flowering and seed-producing success of grassland species and plant species in general?
Location: Southeast Finland.
Methods: Plant species composition, flowering and seed production success were studied in road verges (1) mown once in August and (2) mown at the end of June and August. Flowering shoots were counted and phenological phases were estimated four times during a growing season.
Results: The numbers of flowering or seed-producing species and shoots indicated that mowing once a year corresponding to the timing of traditional management was markedly better than mowing twice a year. The difference between the management groups was greatest at the end of July when the number of flowering species was 43% and the number of flowering and seed-producing shoots 76% less after the first mowing than in the still unmown sites. The species avoided early cutting either through the timing of flowering or due to their growth form. Early season mowing had no effect on the occurrence and seed-producing success of grassland species and the first flowering species. Seed production of grasses succeeded poorly in the verges mown twice.
Conclusion: Mowing once in August resulted in higher seed production in general, but mowing twice a season might be a better way to manage young verges on nutrient-rich soils. The useful qualities of the management options should be considered locally when planning road verge management.
Nomenclature: Hämet-Ahti et al. (1998).