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Problems and opportunities - Habitats/species


Direct land take causing loss of habitat and possibly fragmentation are common to all forms of linear transport infrastructure, but mostly the land take footprint of roads is larger. The direct land take effects depend on the diversity of the landscape. However, compared to railways and canals, the roads have the most flexible alignment, providing more opportunities to avoid valued habitats.


Barrier effects arise whereby animals are unable to easily cross the route as a result of fencing, structures, traffic flow and, in colder climates, walls of snow or steep banks in the case of waterways. The consequences can result in:


– a threat to the viability of affected populations as a result of genetic isolation and/or of isolation from a seasonal food source particularly for migrating species,

– a risk of accidents to road and rail users when larger animals attempt to cross the carriageway/line,

– negative affects to measures designed to rescue vulnerable populations (as an indirect consequence of a barrier).


To accommodate animal movements requires a knowledge of the behaviour and territories of affected /vulnerable populations. In the case of larger mammals like the moose (Alces alces) it can relate to an extensive area. The incorporation of crossing points is easiest if known about early in the design process. To channel their use, crossing facilities need to be accompanied by protective fencing and associated planting. Fencing requires a long-term maintenance commitment if it is to be effective. Subsequent monitoring can check the appropriateness of the particular design and result in fine adjustments taking place. Spatial planning in the wider area must protect ecological corridors connecting the crossing points. This may be the responsibility of a different authority to that concerned with transport related issues.


The physical construction of a transport route can block natural drainage patterns of water and of air. This can cause changes to the adjacent habitat, for example drying out of a valued wetland with resultant changes to the associated flora and fauna including loss of species. Other changes to wetland habitats can result from the diversion of numerous small streams into one side ditch. Early in the project design specialist skills are required to assess the ecological consequences of such changes, and the need for remedial measures as well as areas of opportunity. In an impoverished habitat this can be put to good effect through habitat creation.


In landscapes adversely affected by development or economic activities, opportunities should be taken for positive landscape enhancement to develop new landscape qualities and structures in association with the route, rather than the more limited screening or integration function. Such planning can be undertaken in conjunction with enhancement of biological diversity including as a contribution to specific targets in biological diversity action plans or strategies. To ensure implementation, wider scale works outside the boundary fence need to be related to land acquisition, or undertaken by agreement on a voluntary basis, and/or with fiscal incentives/ grants etc.


In areas of intensive agricultural production or degraded landscapes, the design of transport schemes can provide major opportunities for improving the wildlife value of the adjacent area; for example planting along the embankment/verge to provide a linkage between two woodlands important for butterflies but otherwise separated by arable production (Bickmore 1992). Verges can be designed as a linear nature reserve with possibilities for the Emerald Network. Small severed areas of adjacent land can likewise be developed and managed for wildlife benefit. Care needs to be exercised to ensure that such enhancement will not attract species that subsequently get killed by road or rail traffic.



The frequency of vehicles along roads creates the greatest risk for animal crossing movements with consequential danger to drivers and the species concerned. Crossing facilities for low-flying animals, e.g. lesser horseshoe bat (Rhinolophus hipposideros), barn owl (Tyto alba) can be problematic particularly for roads, although in some areas roadside verges can be important hunting grounds for these species.


In addition to negative changes arising from land take and fragmentation are those caused by effects on land beyond the road boundary such as lighting. For reasons of safety lighting is associated with roads in built up areas or around junctions and can be disruptive to the behaviour of certain species of bird, bat and night flying insects, a problem particularly near known populations of rare species. Similarly effects to adjacent land are associated with emissions arising from vehicles causing air and water contamination. Some studies have suggested that breeding birds are affected by the noise of traffic. Clearly knowledge of adjacent sensitive habitats and species is critical.


The large surface area of roads can result in a surge of surface water run-off into neighbouring watercourses. Water balancing/attenuation ponds are designed to minimise this effect. They can be adapted also to provide a beneficial wetland habitat; however, maintenance of the primary function of the ponds is crucial to their success. Water storage ponds may be required for fire control and can similarly be adapted. Such opportunities may provide positive benefits for wildlife at little extra cost and can help offset other negative effects. The application of best available technology has resulted in the use of porous tarmac, which can reduce surface water run off as well as have other benefits such as reduced spray and traffic noise.




The effects of railway-induced fragmentation and associated habitat severance have not been extensively examined. Compared with roads the intermittent frequency of the trains provides certain wildlife with a greater opportunity to safely cross the track. (Tunnelling is discussed on the section on construction). Work to date suggests the ability to cross is quite variable between species. Migrating amphibians are known to have difficulties in crossing railway ballast (COST 341). One monitoring study confirmed that greater attention to fine detail would have increased use of the crossing facility by certain vertebrates, for instance the planting of cover near the entrances. More important was the relative location of the crossing to the particular species concerned (Rodriguez et. al. 1996). Fencing did not always prevent vertebrates gaining access onto the line.


In some locations railway embankments are associated with a relatively diverse specialist flora. The embankments provide some opportunities for the development of wildlife corridors but unlike roads these can be of limited length (compartments) on account of the restricted distance between the ballast and the side wall of culvert bridges, on some bridges the track bed may include holes. Efforts to link areas of semi-natural habitat outside the fence line can be thwarted by the reliance on adjacent land occupiers (Bakker 1997).


Other measures are under study include adapting ballast size in selected places to facilitate the crossing of amphibians, reptiles and small mammals, the use of anti-perch devices, and extra large insulators to reduce the risk of electrocution, and winter feeding of certain species of wildlife to encourage them to stay away from railway lines (Berthoud 2001).


Railway embankments may be attractive to certain species that accept disturbances caused by the trains but this is not beneficial always. For example local rabbit populations have reached unacceptable levels, damaging adjoining crops.







Canals can cause wide-scale hydrological changes to the surrounding area including drying out of the flood plain with associated changes to sensitive wetland habitats and species. Changes to species can occur when waterways from different river catchments are connected with the risk of introducing aggressive species, or a modified biochemical composition (Kurstjens 2000).


Many long established canals have developed a diverse aquatic and bank side flora and fauna including species typical of lakesides. On this account a number of canals have been given legal protection, including as Special Areas of Conservation. This has implications if boat traffic increases.


Regularisation of flow, canalisation and over widening/deepening required to meet navigation objectives of rivers have resulted in the loss of riverine forests, filter feeding macro invertebrates, and natural herbivores and their associated predators. An alternative more sustainable approach is that the condition of the river dictates the type of vessel that can use it for navigation.


Both canals and navigable rivers can provide a barrier to movement on account of steep sided banks preventing animals from getting out of the water. Dams can prevent the movement of fish along the water course with wide reaching consequences for the rest of the river, for example in the case of migrating salmonids.


Along canals adjustments to the bank profile can assist crossing animals and thereby reduce the effects of severance. At the same time such adjustments can provide an area for the development of an emergent flora (Alberts 1991, and CUR 1999).


New dams and locks associated with waterways are of concern on account of the ecological consequences from regularisation of flow. Recent development of the use of screens to reduce erosion can lead to the loss of groins to give the river a more natural appearance. Other examples of measures to lessen the adverse effects caused by navigation include the construction of side channels to avoid the need for dams, to create a fish pass, or to re- establish the riverine flora and fauna.





Implications of construction and improvement


Extensive earth moving is the main feature of most transport construction works (Table 5.3). This requires large machinery and land for temporary storage of topsoil, subsoil and dredgings in the case of waterways. Climatic conditions can cause short-term dust and/or run-off from the exposed surfaces with watercourses and sensitive habitats at risk from long-term damage. Large machinery emphasises the need to clearly protect/fence off the adjacent sensitive habitats or features from “straying” vehicles. Environmental management systems should assist in identifying these and other such risks.


The construction of a railway is similar to a road but tunnelling or cut and cover may be more frequent. This can assist with long term visual and biological integration, provided adequate consideration is given to the disposal of large amounts of surplus material. Such effects should not be under estimated. With imagination surplus spoil may provide a positive opportunity. The long term benefits of cut and cover tunnels need to be assessed in terms of the destruction (loss) of the habitat during the construction phase. With high speed passenger trains, passenger pressure pulses cause discomfort and from this aspect tunnels are undesirable.


Upgrading the existing railway lines may be constrained to the present land ownership take resulting in the loss of valuable bank side habitat. Access for ecological surveys along railways can be restricted on account of Health and Safety and disruption to existing services (Railtrack 2000) with implications for the quality of EIA and management. Longer trains associated with upgrading may require the extension of station platforms. Upgrading may provide opportunities for adapting crossing points for use by certain species.


Construction of new canals is relatively infrequent. Construction works are of a similar nature to road and rail and relate to earthworks. Upgrading of rivers for navigation includes activities such as the construction of dams and dredging. Over deepening to accommodate larger sized vessels can be a specific problem. The disposal of the arising wet material requires large areas of land nearby.  

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