It was a Saturday of hedgelaying at Crane Park Island that first introduced me to the Crane Corridor, which lies along the River Crane, on the boundary of London Borough of Richmond and London Borough of Hounslow in West London (UK). Since then I have returned on a number of occasions to explore the mosaic of diverse habitats that line the river channel from source to mouth. Most recently, as part of a biodiversity module of my MSc degree, a small group of us had carried out a Phase 1 Habitat Survey of the broadleaf woodland on and around Crane Park Island (after gaining permission from the LB of Richmond).

Fig.1 Crane Park Island - willow carr (i.e. wet woodland) © Veronika Moore

The Crane Corridor is a 5km-long linear corridor of open space around the River Crane, extending from the east of Heathrow Airport, though Hounslow Heath to Twickenham within the Greater London area. As a Site of Metropolitan Importance, a unique assemblage of dry and wet habitats (i.e. woodland, scrubland, reedbed, meadow and ponds) borders it on both sides, however it is predominantly a wooded corridor. Additionally, willow-alder woodland occurs in several locations, which is a rare habitat in London (Fig.1).

Fig.2 River Crane Corridor, Crane Park section (Ordnance Survey, 2012)

The Crane Corridor covers approximately 33 ha and contains two Local Nature Reserves (LNR), namely Crane Park Island LNR and Pevensey Road LNR (see designations below). Despite its heavily urbanised setting, it is considered as one of the major wildlife corridors of London given that it provides essential habitat for a wide variety of fauna and flora, including UK BAP priority species such as Water vole (Arvicola terrestris), Stag beetle (Lucanus cervus), Great crested newt (Triturus cristatus) and Soprano pipistrelle bat (Pipistrellus pygmaeus). The ecological management of the Crane Corridor is divided between London Borough of Richmond, London Borough of Hounslow, London Wildlife Trust and Friends of the River Crane Environment (FORCE).

Designations:

• M076 Site of Metropolitan Importance
• Metropolitan Open Land
• Metropolitan Green Belt
• Crane Park Island LNR
• Pevensey Road LNR
• Green Flag Award 2012/13

Major Habitats of Crane Park Island LNR:

• Mature woodland - broadleaf
• Meadow
• Riverside/ riparian habitat
• Willow carr/ wet woodland
• Reed beds

History

The Crane Corridor has a long-standing historical association with the gunpowder industry. The once celebrated Hounslow Gunpowder Works opened here in 1766 and after it ceased to operate in 1926, the subsequent owner sold part of the site for housing and part to Twickenham Council who turned it into a public park in 1935. Explosions were an unfortunate consequence of gunpowder manufacture (Fig.4); hence Horse chestnut (Aesculus hippocastanum) was planted around the powder mills and buildings to help contain frequent explosions. Moreover, Crack willow (Salix fragilis) which grows along the banks of the River Crane, was used as a primary material for charcoal manufacture. The original site of Crane Park Island contained a millpond to drive the machinery; therefore the island remains a site of important archaeological remains. The nearby Shot Tower, built in 1828, served as a watchtower to alert workers to fire hazard; it is now a listed building and a nature study centre (LB Richmond, 2010).

Fig.4: A powder mill explosion, 1772 (The Illustrated London News)

The woodland (surveyed during this ecological assessment) appears on early maps from the beginning of the 19th century and has fairly irregular boundaries. Originally, it lay along a parish boundary, bordering with a large area of common land. Under the Enclosure Act 1800, the common land, which served as pasture woodland for cattle grazing and fire wood collection, was divided up and sold (Twickenham Museum, 2012). In addition, the presence of ancient trees (i.e. a Horse chestnut, which had its crown blown off during WW2) and the history of coppicing or pollarding indicate that the woodland is of ancient origin.

Woodland habitat survey

For copyright reasons, only a brief synopsis of the survey can be published here.

In total, 24 species of woodland flora were identified during the survey, ground flora being the most abundant, followed by understorey and canopy species. No rare or priority species were found. Based on Rodwell’s national vegetation classification guide to woodland, the tree density of the sampled area was most closely related to the W8e classification of woodlands and scrub (namely Fraxinus excelsior - Acer campestre - Mercurialis perennis woodland with Geranium robertianum sub-community), but there were some similarities with other classes (Rodwell, 1991; Hall et al, 2004). Species density was also compared against the dataset on the National Biodiversity Network and the distribution of sampled species was consistent with a 10-km2 BSBI distribution maps.

Existing management

The Crane Corridor features prominently in both the Hounslow and Richmond Habitat Action Plans (HAP) (LB Hounslow & Richmond, 2012). With regards to the Richmond HAP for Broadleaf Woodland, management action entails the containment of non-native species such as Sycamore and the cutting back of woodland areas to prevent the encroachment of open spaces (Richmond Biodiversity Group, 2009a). Moreover, the Richmond HAP for Reedbeds promotes the restoration of reedbed habitat along the River Crane, which has suffered significant decline as a result of inadequate management (Richmond Biodiversity Group, 2009b). Rotational cutting of reedbeds is already taking place in the borough’s nature reserves. The Hounslow HAP places particular emphasis on biological monitoring, surveying and habitat management along the Crane Corridor (Hounslow BAP Partnership, 2011), including periodic coppicing of trees.

By and large, the current grounds maintenance of Crane Park involves litter collection, cutting of formal grass, maintenance of paths and park furniture and invasive species control. Woodland maintenance is kept at a rather modest level with emphasis on the retention of native species and careful removal of non-native trees (where deemed necessary). The retention of dead wood for the creation of habitat piles is also encouraged (LB Hounslow and Richmond, 2012). In terms of river management, the London Wildlife Trust is in charge of cleaning up the river to improve stretches of sluggish river flow and retain/ enhance existing biodiversity (i.e. the population of Water voles). The conservation charity also monitors water quality to identify sources of pollution.

The majority of open spaces along the Crane Corridor are central to both Hounslow and Richmond HAP; therefore the current management of most habitats is considered adequate. However, there is still great potential for further enhancements of the site’s biodiversity value through better landscape design and management and periodical biological recording. Additionally, due to the presence of several UK BAP priority species within the corridor, any future development plans will need to comply with the Wildlife and Countryside Act 1981.

1. Baxter, A. (2011) London’s Natural Signatures: The London Landscape Framework – 12. Hounslow Gravels. Sheffield, UK: Natural England.
2. British History Online (1962) Twickenham – A History of the County of Middlesex: Volume 3 (pp. 139-147) [online]. Available at: http://goo.gl/VYuEi.
3. Fitter, R. & Fitter, A. (1984) Grasses, sedges, rushes and ferns of Britain and Northern Europe. London, UK: Collins.
4. FORCE (2012) Nature in the Crane Valley [online] Friends of the River Crane Environment. Available at: http://goo.gl/3OL8t.
5. Hall, J.E., Kirby, K.J. & Whitbread, A.M. (2004) National Vegetation Classification: Field guide to woodland. Peterborough: Joint Nature Conservation Committee.
6. Hounslow BAP Partnership (2011) Hounslow Biodiversity Action Plan 2011 – 2016. Hounslow: LB Hounslow.
7. LB Hounslow & Richmond (2012) Green Flag Awards 2012: Crane Park Management Plan. Hounslow and Richmond: London Boroughs of Hounslow and Richmond upon Thames.
8. LB Richmond (2003) Overview of Nature Conservation Value: Crane Valley Masterplan Area. London, UK: Waterman Environmental.
9. LB Richmond (2010) Local History Notes: The River Crane and Gunpowder Mills. Richmond upon Thames: London Borough of Richmond upon Thames.
10. Nature Conservancy Council (2003) Handbook for Phase 1 habitat survey – a technique for environmental audit. 2nd edition, JNCC, Peterborough.
11. Richmond Biodiversity Group (2009a) Broad-leaved Woodland Habitat Action Plan. Richmond upon Thames: LB Richmond.
12. Richmond Biodiversity Group (2009b) Reedbeds Habitat Action Plan. Richmond upon Thames: LB Richmond.
13. Rodwell, J.S. ed. (1991) British Plant Communities. Vol I: Woodlands and scrub. Cambridge: Cambridge University Press.
14. Twickenham Museum (2012) The Twickenham Museum: Whitton and the River Crane [online]. Available at: http://goo.gl/mtZ4t.