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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. Roads 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. Railways 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. Waterways 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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