Mowing management in the roadsides

Roadsides constitute an increasingly important part of the living environment. Nowadays there are more than 160,000 hectares of public road verges under regular mowing management in Finland. Since the amount of mowed verges is at least fivefold in comparison to semi-natural grasslands managed either by mowing or by grazing, road verges may work as substitute habitats or refugia for several grassland species, in particular the butterfly fauna and meadow flora adapted to continuous grassland management. However, there is scant information about the importance of the roadside habitats and their management to grassland biodiversity.

The effects of mowing on roadside biodiversity is designed, on the one hand, to improve our knowledge about the diversity of fauna and flora in roadside habitats in Finland. Two groups of insects (butterflies and day-active moths) and the meadow flora used in the study consist of several species indicative of habitat quality and environmental change. On the other hand, special attention will be paid to the evaluation of the effects of the type and the intensity of mowing on the composition and abundance of these groups on road verges. This information is intended to help in planning road verge management in order to maintain and even increase the biodiversity in the future.

The field data was collected between 2004 and 2005 in co-operation with the University of Joensuu Department of Biology and the Finnish Road Administration. The study was carried out along the road network in the Imatra-Lappeenranta region, SE Finland. Representing the verges of motorways, town roads and rural roads, the study sites were classified according to the share of the mown area (fully mown, partially mown) and the timing of mowing (early or late summer). Topography, soil properties and the breadth and age of the verge were among the criteria used for the primary selection of the sites.

At each site butterflies and moths were studied along a transect route of standard length (250 m), censused once a week between early June (week 23) and late August (week 35). The communities in the habitat groups differing in respect of the area and the timing of mowing were compared using the diversity indices and multivariate methods. Suggestions for better management of road verges were given on the basis of the results.

A mark-release-recapture (MRR) method was used to assess the movements of some butterfly species in relation to the mowing of roadsides. Individuals were netted, marked, released and recaptured in sections of mown and non-mown parts of the verges on a daily basis. The MRR study provided information on whether the individuals remain in the verge habitat if it is mown only partially near to the road or if some sections are left completely intact.

The vegetation data for each site was collected on five 1x1 metre sample plots located systematically along the butterfly transect route. All plots were examined at least three times during the study period in order to reveal the impact of the intensity and timing of mowing on the flowering of the meadow vegetation. In addition, the presence of valuable meadow species and the abundance of nectar plants for butterflies was evaluated throughout the study area.

The final project report has been published in the series of publications of the Finnish Road Administration. Combining the results with those achieved in the earlier study (TIELI, 2001-2003), the research group was able to compile a practical field guide to a sustainable way of managing road verges with a view towards securing a higher level of biodiversity.