|PROPOSED GREATER BRISTOL BUS NETWORK
A4174 RING ROAD COLDHARBOUR LANE TO M32 JUNCTION
A series of ecological surveys of the area affected by a proposed bus lane along the existing A4174 ring road was carried out, largely covering the habitats on the verge and embankment of the existing road, but also extending onto adjacent fields. The aim of this report is to describe the findings of these surveys.
The following surveys have been carried out:
Vegetation: An extended Phase 1 habitat survey of the corridor and adjacent areas has been carried out and plant species lists with abundance assessment have been compiled;
Amphibians: The corridor and surrounded areas have been checked for habitat potentially suitable for great crested newts and other amphibians;
Badgers: The corridor and, as far as possible, all areas within thirty metres have been checked for badger setts and other signs of badger activity;
Reptiles: Refugia (squares of roofing felt) have been laid in suitable habitat along the corridor and have been checked on fifteen occasions (as part of a translocation operation, reported on separately, they were supplemented and checked on a further 31 occasions);
Birds: All birds seen and heard on four early morning visits have been mapped;
Bats: The corridor has been assessed for potential roost sites in buildings and trees. Three activity surveys of the corridor, using bat detectors, have been carried out on 16th June, 29th June and 23rd July in conditions ideal for bat survey. On each occasion two surveyors each using Pettersson D230 heterodyne and frequency division bat detectors, and one using a Zoom H2 digital recorder walked the site for three hours, commencing ten minutes before sunset;
Invertebrates: A visual search of any habitat of potential value for invertebrates has been made to date on five occasions;
Hedgehog: The site has been checked for hedgehog droppings and a search for hedgehogs has been made during other visits, in particular during the bat activity surveys.
It should be noted that full access to farmland adjacent to the highway land has not been possible. The implications of this for the various surveys are considered in the assessment section below.
The survey area consists of the existing verge on the northern side of the A4174, together with a strip of land along the edges of the adjacent fields. The verge has a strip of grassland, which is narrow in most places but slightly wider at the western and eastern ends of the section, and a wider strip of secondary woodland and scrub. The adjacent fields consist of permanent grassland and are divided by hedges. Two streams run under the road.
Species lists are included as Appendix 1.
The grassland along the edge of the road is generally tall, with a mix of grass and herb species. The most frequent grass species is false oat-grass (Arrhenatherum elatius) with other species present in good quantity including red fescue (Festuca rubra), cocksfoot (Dactylis glomerata) and rough-stalked meadow-grass (Poa trivialis). Frequent herb species include ribwort plantain (Plantago lanceolata), wild parsnip (Pastinaca sativa) and ox-eye daisy (Leucanthemum vulgare), with patches of stinging nettle (Urtica dioica). The diversity of plants is greatest at both the western and eastern ends of the section. A bank above Maules Lane and the verge between there and the western end of the site has frequent meadow vetchling (Lathyrus pratensis), hedgerow bedstraw (Galium mollugo) and sweet violet (Viola odorata) with a small quantity of common broomrape (Orobanche minor). At the eastern end of the site the verge becomes wider around the M32 roundabout. Species here include meadow vetchling, black knapweed (Centaurea nigra), meadow cranesbill (Geranium pratense), grass vetchling (Lathyrus nissolia) and ragged robin (Lychnis flos-cuculi).
The strip of woodland is largely the result of planting of tree species, which include Norway maple (Acer platanoides), lime (Tilia x vulgaris), ash (Fraxinus excelsior) and hornbeam (Carpinus betulus). In places there is a dense understorey of hawthorn (Crataegus monogyna), blackthorn (Prunus spinosa) and bramble (Rubus fruticosus agg), but in most places the understorey is sparse. The ground flora is dominated by ivy (Hedera helix), with good quantities of ground-ivy (Glechoma hederacea), cow parsley (Anthriscus sylvestris) and goosegrass (Galium aparine). Other species present include bluebell (Hyacinthoides non-scripta), stinking iris (Iris foetidissima) and male fern (Dryopteris filix-mas).
The fields at the western end of the site have improved grassland, dominated by perennial rye-grass (Lolium perenne) with few other plant species present and one field has recently been re-sown. The fields at the eastern end of the section have semi-improved grassland, dominated by perennial rye-grass but with a variety of other grass species including sweet vernal grass (Anthoxanthum odoratum), meadow foxtail (Alopecurus pratensis) and crested dogstail (Cynosurus cristatus). Herb species present include large quantities of meadow buttercup (Ranunculus acris) and smaller quantities of species such as common sorrel (Rumex acetosa) and cuckoo flower (Cardamine pratensis).
The hedges that divide the fields are dominated by hawthorn and English elm (Ulmus procera), with other species including elder (Sambucus nigra), blackthorn, dog rose (Rosa canina agg) and field maple (Acer campestre). No hedge has, as far as could be seen, more than four woody species.
The stream close to the western end of the site does not have wetland vegetation, but the stream at the eastern end of the site supports water starwort (Callitriche sp), soft rush (Juncus effusus) and hairy willowherb (Epilobium hirsutum).
There are no ponds either on or adjacent to the survey site and the streams that cross the site do not appear suitable for amphibians. Refugia on the site were checked on a total of 46 occasions (including the slow worm translocation) and no amphibians were recorded.
The closest pond to the site is a large ornamental lake in the grounds of the Holiday Inn to the south of the A4174. This is heavily stocked with carp and other fish species here include large populations of tench, perch and roach. As a consequence it does not have submerged vegetation and the populations of predatory fish make it unsuitable for great crested newt.
The closest pond on the northern side of the road is just over 500 metres to the north-east. A series of ponds has been created here as the receptor site for a great crested newt translocation scheme.
Evidence was found for low-level use of sections of the verge by badger in the form of fairly well-defined but not particularly well-use tracks running through tall grass and dense scrub. At various locations these tracks cross the boundary onto adjacent farmland to the north. The level of activity increased slightly in the autumn, possibly as a result of increasing visits to the site by badgers feeding on fruit. No significant foraging sign, latrines or dung pits were found.
There has been substantial rabbit burrowing along significant sections of the verge, especially along the junction between the verge bank and level land to the north. The soil is relatively sandy and makes for relatively wide-bore rabbit burrows such that the size range overlaps with that of badger. This made it difficult to confidently establish lack of use of some burrows by badger.
Three burrows at the location shown on the attached map are large enough for use by badger, are associated with a badger track and in one case contain badger hair within the spoil. Spoil heaps associated with these burrows are relatively small. The burrows probably all join up underground; all appear to at least occasionally be used by rabbit; and they link with a number of other entrances that are more typical of rabbit and too small to be used by badger.
Various other burrows were large enough for use by badger but no supporting evidence for use by badger could be found (whereas all appear to have been used by rabbit).
The only species recorded was slow worm. Small numbers (up to six) of this species were recorded throughout the site but concentrated at its eastern end. A translocation exercise was carried out and is the subject of a separate report.
Large numbers of common pipistrelles and noctule bats were recorded feeding along the hedge and over highway lights during the first two surveys and large numbers of common pipstrelle (but only one noctule) were recorded during the third survey. Most records were made at the western and eastern end of the site, with relatively few in the central section. The totals recorded are as follows:
16th June: Common pipistrelle: twelve records (nine foraging along hedge, three foraging over lights)
Noctule: thirteen records (ten foraging along hedge, three foraging over lights).
29th June: Common pipistrelle: fifteen records (three commuting, nine foraging along hedge, three foraging over lights)
Noctule: ten records (one commuting, eight foraging along hedge, one foraging over lights).
23rd July: Common pipistrelle: seventeen records (all foraging along hedge)
Noctule: one record (foraging along hedge).
There are no potential bat roosts on or adjacent to the site. Three commomn pipistrelle flew onto the site from the north early in the survey on 29th June, suggesting that there is a roost to the north of the site.
No other species of bat was recorded.
The following species were recorded at the locations shown on the enclosed map:
Blackbird – two pairs
Great tit – one pair
Greenfinch – one pair
Kestrel – one pair
Long-tailed tit – one pair
Robin – two pairs
Wren – two pairs
The following additional species were recorded outside the breeding season:
Blue tit, chiffchaff, goldfinch, magpie and wood pigeon.
The following species were recorded:
Painted lady, large white, small skipper and large skipper butterflies;
Silver Y, straw dot and Agriphila straminella moths;
Platycheirus cyaneus, Eupeodes luniger, Eristalis pertinax, Syritta pipiens and Episyrphus balteatus hoverflies;
Field grasshopper, meadow grasshopper and long-winged conehead; and Coenagrion puella damselfly.
Comma, speckled wood, gatekeeper and small white butterflies;
Green carpet, silver-ground carpet, Stigmella aurella, Celypha lacunana, Scoparia ambigulais and Anthophila fabricialis moths;
Platycheirus cyaneus, Epistrophe eligans, Syrphus ribesii, Syrphus vitripennis and Helophilus pendulas hoverflies;
Dark bush-cricket; and
The saw-fly Fenusa ulmi.
No droppings or other signs of hedgehog activity were seen.
The nature conservation value of the site has been assessed to determine whether it is of nature conservation value in a national, regional or county context, of either high or low value in a local context, or is of minimal nature conservation value. The assessment has been made using standard ecological criteria, such as size, diversity, rarity and fragility, and reference has been made to suitable guidance, including the UK and South Gloucestershire Biodiversity Action Plans (BAPs). The value of the site for groups not surveyed, such as most invertebrates, has been assessed using information gathered on the nature and structure of the habitats present.
The most valuable habitat on the site is the grassland along the verge of the existing road. Since some of the vegetation here has developed on nutrient-poor sub-soils, plant species typical of unimproved grassland, which have become increasingly rare due to agricultural improvement, have been able to colonise. Such species include meadow vetchling, grass vetchling, common broomrape, black knapweed, common fleabane (Pulicaria dysenterica), ox-eye daisy, wild parsnip, wild carrot (Daucus carota), ragged robin and bird’s-foot trefoil (Lotus corniculatus). This is a good diversity and some species are present in good quantity, but the area of habitat present is small.
Three of the grassland species are defined in The Flora of the Bristol Region as Avon Notable Species on account of their local rarity. These are as follows:
Grass vetchling – locally frequent at the eastern end of the sitee;
Common broomrape – rare on the cutting to the east of Maules Lane; and
Blue fleabane – rare at the eastern end of the site.
A further three Avon Notable Species recorded, Danish scurvy-grass (Cochlearia danica), greater sea-spurrey (Spergularia media) and distant saltmarsh grass (Puccinellia distans), are halophytes, present on the road edge here because the road is salted.
The grassland along the road verge is of high nature conservation value in a local context.
The woodland is the result of planting and the resulting habitat is dense and lacks structural diversity. The ground flora is generally undiverse and typical of woodland habitats of recent origin. There are some woodland species, however, most notably bluebell. The woodland provides some habitat for animals (see below).
The woodland is of low ecological value in a local context.
The fields at the western end of the site have been intensively farmed and are overwhelmingly dominated by perennial rye-grass. Fields such as this are frequent throughout lowland Britain and are readily recreatable. They are of minimal nature conservation value.
The fields at the eastern end of the site are more diverse. They appear to be semi-improved, which means that agricultural improvement has excluded most grassland species but that the intensity of this improvement has not been sufficient to exclude all such species. They do not appear to be particularly diverse, but further survey could reveal additional species.
These fields are of low nature conservation value in a local context.
The hedges that divide the fields appear to be rather low in diversity and there is no indication that they would qualify as Important Hedgerows under the 1997 Hedgerow Regulations.
The hedges are of low nature conservation value in a local context.
There are no breeding habitats for amphibians either on or adjacent to the survey site. The closest pond is to the south of the existing ringroad and is unsuitable for most species, including great crested newt, because of the absence of submerged vegetation and the abundance of predatory fish. The closest suitable breeding habitat for this species is approximately 500 metres away, right on the edge of the range over which this species is thought to move over terrestrial habitats. The survey site is separated from this breeding site by a stream and by inhospitable habitat in the form of intensively managed fields, so it is thought highly unlikely that it would move this substantial distance to reach the survey site. In total (including during the translocation) refugia on the site were checked on 46 occasions without amphibians being recorded.
There is evidence of some badger activity on the edge of the site and it provides foraging habitat of low value for the species. Two rabbit burrows are infrequently used outlier setts.
The site is used by a population of slow worms. Data from the survey suggests that this population is small and the small number of juveniles recorded suggests that they are not breeding successfully. Slow worms are legally protected and are a BAP priority species. The site is of some importance for this species but the area of suitable habitat is very limited, with most of the grassland being mown short in late summer and the woodland and scrub being too shady for this species. This suggests that the long term viability of the site for this species is limited.
There are no buildings on the survey site, and no trees with holes or crevices that could be used as bat roosts. The results of the bat surveys suggest that the site is not of importance as a commuting route, but that it is of considerable importance as a foraging site, with the road lights being a favoured feature, presumably because of the insects they attract. The woodland habitat provides a foraging habitat of secondary value.
Birds are present in low numbers and diversity, probably because of the lack of structural diversity in the woodland and perhaps because of proximity to the ringroad. The only significant record is that of kestrel, which is breeding in trees near the western end of the site. This species is of conservation concern due to recent population declines. The average breeding population in South Gloucestershire over the last decade is 22 pairs.
The site is of some value for birds because it supports a pair of kestrel.
The grassland on the verges has features that suggest that it is likely to be of value for invertebrates, including a diverse flora, lack of management and diversity of habitat structure. However, invertebrates have been recorded in small numbers and low diversity only. This may be largely due to the small extent of the habitat. The species of insect recorded are all common and widespread. It appears that the invertebrate populations are of low nature conservation value in a local context.
No hedgehogs or signs of hedgehog have been recorded, although some of the habitats appear suitable. The site’s position between two major roads may explain this apparent absence.
The following features are of importance:
Grassland on road verges: of high nature conservation value in a local context;
Woodland on road cutting: of low nature conservation value in a local context;
Adjacent fields in eastern part of site: of low nature conservation value in a local context;
Nesting habitat for a pair of kestrels;
Slow worm population;
Bat foraging habitat.
The proposal to widen the road by creating a bus lane will affect some of the features described above, but it also offers opportunities for mitigation. This section describes the impacts as they would occur without mitigation; opportunities for mitigation are then discussed in the following section.
The grassland of high nature conservation value in a local context and the woodland of low nature conservation value in a local context would be lost. This would have a moderate adverse impact.
A strip along the edges of the adjacent fields would be lost. Some of these are of low nature conservation value in a local context and their loss would have a minor adverse impact.
The habitat of a small population of slow worms would be lost and the animals, without mitigation, would be killed. This would have a moderate adverse impact and killing of the animals would be illegal.
Foraging habitat for bats would be lost. This would have a moderate adverse impact.
Nesting habitat for a pair of kestrels would be lost. It is unlikely that availability of nesting habitat is a limiting factor on the population of this species, but this could have some minor impact on the population of this species.
The scale of indirect impacts is limited by the fact that the survey area is in a triangle of land between the ringroad and the M32 motorway. Species using the area are therefore already accustomed to the associated impacts such as noise. Furthermore, no habitats of significant nature conservation value have been found adjacent to the survey site.
The proposed bus lane would have some potential impacts, such as extension of lighting over a slightly larger area. However, the only group likely to be affected by lighting is bats and the survey results suggest that those species present are making use of the existing lighting for foraging. None of the bat species known to be sensitive to lighting have been recorded.
The scheme should result in a decrease in road traffic and there should therefore be no rise in road deaths suffered by wildlife.
The proposal would cause no significant increase in habitat severance or loss of wildlife connectivity since the existing roads already sever wildlife corridors in the area.
There are small streams running under the road and uncontrolled discharge of run-off into these would have adverse impacts by polluting local water courses.
Loss of habitats on the existing highway land could be mitigated by habitat creation on the newly formed verges and embankments.
Grassland on Verge
Loss of grassland should be mitigated by creating new areas of grassland on nutrient-poor substrates; it is essential that fertile soils are not used because these limit diversity. These soils should be treated to avoid compaction and can be left for natural colonisation, or sown with red fescue at a low application rate (4g per m2) to provide a sparse sward that leaves niches for colonisation.
Only small areas of diverse grassland would be lost and these have colonised a relatively recently created site, so that features associated with ancient habitats are absent. If an adequate area of grassland could be created then full mitigation or even enhancement could be achieved.
Woodland and Hedges
The loss of woodland habitat could be mitigated by new planting. This should be dominated by native species and should include a higher proportion of shrub species than are present in the existing habitats. Planting would also provide mitigation for the loss of lengths of field hedge. If this is carried out then full mitigation could be achieved.
Grassland in Fields
A small area of semi-improved grassland in adjacent fields would be lost. This impact could be mitigated by creating species-rich grassland or wetland habitats around the proposed drainage feature. The area should be formed using nutrient-poor sub-soils and at a variety of depths, so that a diversity of soil moisture is provided. The area of habitat created would be smaller than that which would be lost, but the new habitats could be more diverse than those lost and the degree of mitigation would therefore be complete.
The scheme should be designed to prevent run-off entering local water courses directly. This should avoid any potential impacts associated with pollution.
In order to avoid killing slow worms a translocation operation would be required. The area to be affected would need to be fenced with reptile-proof fencing and refugia placed in the area and used to trap and remove slow worms. This operation would have to be carried out between April and October. The slow worms would have to be removed to a receptor site. A nearby area of highway land may prove suitable. Some enhancement work in the receptor site might be required in order to increase its carrying capacity for slow worms. A destructive search, when an ecologist is present during the initial stages of construction, would also be required.
It is reasonable to assume that the bats that feed around the existing road lights will feed around replacement lights, so the conclusion of the surveys carried out to date is that specific mitigation for bats is not required. However, wider impacts should be avoided by using sodium instead of mercury or metal halide lighting and by using directional lighting as far as possible.
A line of trees and shrubs, dominated by native species, should be planted along the new embankment to re-create foraging habitat for bats.
The loss of a breeding site for kestrels could be mitigated by providing a nesting box for this species in a nearby tree. Such nest boxes are readily available.
All active birds’ nests are protected by law and clearance of trees and scrub, including bramble, should not be carried out during the period 15th February to 30th September.
The rabbit burrows used as badger setts should be closed under supervision of a licenced person. This will involve installing one-way gates across the burrows and monitoring these until it is clear that badgers are no longer using the burrows, which can then be dug out by hand. A licence application for this operation has been approved by Natural England. The new verge should include a belt of tree and shrub planting in order to replace the badger commuting route. It would be beneficial to include apple and plum trees in the planting mix; these should be planted at the bottom of embankments, away from the highway, to minimise the risk of badgers straying onto the road.
Wessex Ecological Consultancy