HS2 chalk grassland project attracts wildlife

Wildlife is already colonising the Western Slopes, a 127-hectare artificial chalk grassland created by HS2 near the Chilterns tunnel. The project, which is due to open to the public next year, has transformed a former wheatfield into a biodiverse habitat featuring grasslands, wet meadows, ponds, and small woods.

The creation of the Western Slopes involved sculpting 10 million cubic metres of chalk and other materials excavated from HS2's construction, particularly from the Chilterns tunnel. This reuse of materials has significantly reduced carbon emissions by avoiding off-site disposal and associated transport.

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Carbon sequestration and habitat design

According to HS2's calculations, the chalk grasslands have the potential to sequester 7% of the total carbon impact from the high-speed line's construction. This is because grasslands store carbon more effectively than regularly ploughed arable land, which releases carbon when tilled. The design incorporates varying topsoils and topographical variations to create a mosaic of habitats.

The vision for the site is a 'wood pasture' landscape, inspired by rewilding projects such as Knepp in West Sussex. This involves a mix of scrub and wildflower glades grazed by herbivores. To facilitate this, four cattle-grids have been installed on local roads, enabling free-roaming cattle within four separate compartments. This grazing is intended to improve soil health and carbon storage, and support species like dung beetles.

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Matt Hobbs, lead ecologist at Jacobs, who oversaw the project for HS2, stated that the project's entire landscape was predicated on finding the best use for the excavated earthworks and soils. "We saw the opportunity to do something different," Hobbs said. "This project is unique."

Biodiversity and ecological features

The site has already seen the return of species such as hedgehog clover, not recorded in Hertfordshire since 1878, alongside water voles, lesser emperor dragonflies, and pyramidal orchids. Further enhancements include the planned spreading of green hay from other calcareous grasslands to introduce more invertebrates, with the expectation that rare butterflies like the Adonis, chalkhill, and small blue will follow. A mammal shelf has also been built into a culvert to allow safe passage for badgers, stoats, and other animals beneath the railway line.

Beside the River Colne, nearly five hectares of new wetlands have been established. These areas have rapidly become home to plant species like club-rush, water mint, and sneezewort, and are now supporting breeding reed warblers and lesser emperor dragonflies. Sightings of water voles have increased, with the new habitat being immediately colonised by the species, which is in significant decline due to habitat loss.

Luke Craner, a senior landscape clerk of works for HS2 contractor Align, noted the changing soundscape, with birdsong and insect hum increasingly audible. "We didn’t have this harmony last year and all of a sudden it’s never silent," Craner said. "This is our hidden gem."

Public access and future development

Footpaths through the Western Slopes are scheduled to open within the next 18 months. However, the western section of the site will remain protected to support ground-nesting birds. As HS2 construction continues, the nature areas are expected to expand further, with a smaller footprint required for the track-building and electrics phase.