Targeted Greening to Control Track-Side Vegetation

To reduce the use of herbicides to control track-side vegetation, the Swiss Federal Railways (SBB) commissioned Agroscope and HEPIA to develop a low-growing plant mix for the track area.

The Swiss Federal Railways (SBB) have decided to restrict the use of chemical synthetic herbicides to an absolute minimum and promote alternative measures in line with the Alternatives to Herbicide Action Plan. One important consideration was that these measures should not reduce the service life of rail infrastructure or compromise train safety or availability.

‘Sowing instead of controlling’

The SBB commissioned Agroscope, the Haute école du paysage, d’ingénierie et d’architecture de Genève (HEPIA) and other partners to investigate whether the targeted greening of verges, maintenance and escape paths and track-side areas could be an alternative to the widespread use of herbicides. The aim was to establish a vegetation cover that supressed problem plants, maintained the safety of rail infrastructure and promoted biodiversity. At the same time, the spread of problem weed species to adjacent farmland was to be avoided through careful species selection.

Five specially developed seed mixes were tested at six sites in the Swiss Plateau. The mixes comprised species which were expected to meet the safety requirements (accessibility on foot, low growth, shallow roots, no trip hazards, no restriction of signal visibility, no impediment to track drainage) and the environmental requirements (ecotypes of native plant species).

Site and mix determine success

The long-term trial showed that successful greening of trackside areas can be achieved using selected species: the seed mixes meet the safety criteria, species diversity increases, soil temperature decreases, and the quality of the track-side landscape is enriched.

Two site factors are key to the establishment of the sown plants:

1. The organic matter content (which takes a number of years to accumulate on the existing, very poor gravelly soils)
2. An adequate water supply in the sowing year to enable the mixes to establish a seed bank in the substrate.

Two mixes, one covering a broad ecological spectrum and the other containing several pioneer species, achieved an average soil cover of over 70% after five trial years on a suitable soil substrate.

The proportion of sown species in the overall vegetation cover was significantly higher than that of spontaneous species at all sites during the trial period. Invasive native and non-native species were significantly scarcer than sown and unproblematic spontaneous species. The sowings increased species richness within the plant community by five species on average.

The study concluded that track-side greening is a realistic alternative to the use of herbicides. However, it will do little to reduce track-side maintenance, since targeted greening also needs regular upkeep. For instance, problematic scrambling and trailing plants from adjacent plots, such as ivy or brambles, still need to be controlled, as do tall plants and invasive non-native species.

Future approaches could involve a combination of mechanical, chemical and biological strategies to ensure optimal sustainability.