Threats
The two most significant threats to the biodiversity of London’s linesides are loss of habitat through development (and occasionally operational requirements), and under-management.

Although the development of railway land began in the 1960s on a number of closed lines, it sharply increased during the 1980s, with the loss of large marshalling yards such as Bricklayers’ Arms and the reduction of space around junctions to housing, for example near Drayton Park, Islington. With privatisation this may set to increase; Railtrack has an obligation to maximise its assets, and this will include selling off redundant land for development. Some railway corridors will be exempt due to their slope, structure or narrowness, but larger areas of flat land (especially those adjacent to existing residential areas) will be under increasing pressure. Only a few railway sites are ‘protected’ in London borough's Unitary Development Plans (UDPs), and efforts should be made by organisations to seek inclusion of the most important areas in the UDP reviews.

The importance of railway linesides lies with the mosaic of habitats that they support. However, rough grasslands and ruderal habitats, by virtue of their decline elsewhere in London, are relatively important in the lineside context. Management to meet operational standards is geared to the prevention of trees growing too near the tracks, especially those with a mucilaginous leaf litter (e.g. sycamore and ash), and a 15m swathe is regularly clear-felled. This is not enough to maintain existing grassland, nor enough to restore grassland that has since turned to scrub and woodland. The likelihood is that on all but the poorest of soils, linesides will become predominantly low sycamore/ash scrub, banking onto stands of oak/sycamore woodland, and maintained as such. Additional management in areas of existing grassland will be required in order to maintain their biodiversity interest; how this will be undertaken in areas not within nature reserves is not known.

Less direct threats include the in-built bias against vegetation within the railway industry, the use of contractors for lineside management and the results of weaknesses in communication and control. In addition, the existing management of the permanent way (through herbicide treatment), potential for widening the rail corridor for new strategic rail links (e.g. the Central Railways proposal of 1996/7), garden encroachment and fly-tipping all threaten lineside biodiversity.

Opportunities
Although it is unlikely that any of London’s railway corridors will be managed primarily for wildlife, there is significant room to enhance their value for biodiversity. In recent years, management guidance produced by the railway companies has begun to take account of ecological issues (e.g. Maintaining the Track Environment, LUL, 1995), and this should be encouraged to progress further. Seeking to restore grassland habitats and manage graded woodland edges, for example, need not compromise the railway companies meeting their operational standards and obligations. Therefore identification of the most important stretches for nature conservation (which will require some further survey) and preparing ‘Conservation Zone Plans’as guidelines for their management by contractors, should be seen as priorities. This would help to target limited management resources effectively. However, the screening and landscape value of tree stands and woodlands should not be under-estimated, and a Habitat Action Plan should take these into account where appropriate. There has been some limited tree-planting on railway land in recent years (e.g. Wandsworth Common), but in light of the priorities to expand the grassland element this should be restricted to identified areas. There may also be opportunities for habitat creation similar to the new ponds created by Railtrack for amphibians at Selhurst.

There is also the potential to seek the creation of more lineside nature reserves managed in partnership between railway companies and conservation groups. These can provide local involvement in lineside habitat management. A number already exist, but there is the opportunity for more throughout London, although it must be recognised that local groups are rarely in a position to manage them without adequate resources.

Railway linesides are seen by many hundreds of thousands of travellers on a daily basis, and for many they are places where they can see the colour and spontaneity of wildlife. Their linear character emphasises the feeling of more or less uninterrupted countryside, almost into the centre of the city. However, there is very little information on railway wildlife or the value of London’s linesides and the potential for raising the awareness of their biodiversity is considerable. This may be through on-train information, station interpretation, lineside signs and leaflets.

Although the ecological interest of London’s railsides has long been recognised (e.g. Fitter, 1945), strategic survey only began with the 1984/5 London Wildlife Habitat Survey. Much has subsequently been reviewed through the work of the LEU, though access to linesides is difficult and, bar the few areas where survey has been more than that viewed from a bridge, platform or moving train, the quality of existing information is poor. An exception is London Underground Limited’s Ecological Report for the Northern Line (1997) and survey of LUL’s above-surface linesides by LEU during 1999. Not all of London’s linesides have been surveyed since 1985, however. The audit has been prepared from stretches identified in the LEU handbooks and other existing information. Therefore, it is not an exhaustive audit and will benefit from more detailed research.

There is further disparity between railside SINCs in these boroughs, as railside land began only to be considered after 1992. Borough surveys prior to this date (e.g. Greenwich, Hillingdon) have virtually no railway land included. Boroughs that have not been surveyed by the Unit (e.g. Bromley, Havering) probably support significant lengths of railside of nature conservation importance; a few are probably some of London’s best (e.g. Elmstead Woods in Bromley). There are therefore opportunities to identify more railway lineside SINCs.