Introduction
Description of Baseline Conditions and Cumulative Impact Assessment
Predicting and Characterising Ecological Impacts
Confidence in predictions
Positive or negative
Magnitude
Extent
Duration
Reversibility
Timing and frequency
Characterisation of the change and impact
Assessment of whether Impacts are Ecologically Significant
Determining ecologically significant impacts
Integrity
Conservation status
Comparison with common current approaches towards impact assessment
Worked example of recommended approach to EcIA
4.1 Assessment of ecological impacts is required at the following stages:
4.2 The starting point for any assessment is to determine which ecological features or resources within the zone of influence are both of sufficient value to be included in the assessment and vulnerable to significant impacts arising from the project. The determination of value should make use of the guidance in Chapter 3. The rationale for selecting features for inclusion in the EcIA will differ, depending on the situation, and so, ideally, it should be agreed through consultation during scoping, see paragraphs 2.35 and 2.36. For those ecological resources or features that are to be included in the assessment i.e. have been 'scoped in', the next step is to describe the changes to the baseline conditions likely to arise from the project and the resulting ecological impacts. If, at scoping these impacts are considered likely to be significant, they should be investigated further and clearly described in ecological terms, before the legal, policy, social or economic implications are considered.
4.3 The following guidance is in accordance with the mandatory requirements of the UK EIA Regulations.
4.4 The assessment of impacts should be undertaken in relation to the baseline conditions within the zone of influence that are expected to occur if the development were not to take place. Thus, for example, if construction is programmed for 2012, construction impacts should be assessed against the baseline conditions predicted to occur in 2012 if the development were not to go ahead. Similarly, if the development is operational from 2013 onwards, the baseline for the EcIA should be the baseline conditions predicted to occur, in the absence of the development, from 2013 onwards.
4.5 It is necessary to predict the future baseline conditions with reference to:
Relevant information may be available in Strategic Environmental Assessments (SEAs)c or Sustainability Appraisals (SAs) that have been prepared for plans and programmes and in the ESs of completed or planned developments.
4.6 Predicting the future baseline in this way enables the EcIA to address cumulative impacts. This is achieved by assessing the ecological impacts of the proposed development in the context of the predicted baseline conditions, thereby assessing the cumulative impact (see example in Box 13).
4.7 The predicted baseline and approach to assessing cumulative impacts should be agreed between all relevant parties during scoping. Close liaison is required between the proponent team and the LPA and/or agencies involved.
4.8 'In-combination' assessments that are carried out as part of 'appropriate assessments' are not required as part of other EcIAs, including EIAs.
4.9 Having identified the activities likely to cause significant impacts (see Chapter 2), it is then necessary to describe the resultant changes and to assess the impact on valued ecological resources. It will be necessary for the proponent's ecologist to liaise with other members of the proponent's team as the changes to be considered may relate, for example, to noise, air quality, hydrology or water quality.
4.10 This guidance recommends that the process of identifying impacts should make explicit reference to aspects of ecological structure and function on which the feature depends. Some of the elements that may be considered are identified in Box 12.
4.11 Impacts must be assessed in the context of the predicted
baseline conditions within the zone of influence during the lifetime of the
development. Predicting
the baseline conditions for valued ecological resources should involve consideration
of environmental trends and impacts from built and planned developments,
as described in Chapter 2 and under the heading of 'Integrity' below.
This ensures that cumulative impacts are properly addressed.
Box 12: Examples of aspects of ecological structure and function to consider when predicting impacts.
Available resources
Territory: hunting/foraging grounds; shelter and roost
sites; breeding sites; corridors for migration and dispersal; stop-over
sites. Food and water (quantity and quality).
Soil minerals and nutrients and hydrochemistry.
Solar radiation and gaseous resources.
Stochastic processes
Flooding, drought, wind blow and storm damage, disease,
eutrophication, erosion, deposition and other geomorphological processes,
fire and climate change.
Ecological processes
Population dynamics: population cycles; survival rates
and strategies; reproduction rates and strategies; competition; predation;
seasonal behaviour; dispersal and genetic exchange; elimination of wastes.
Vegetation dynamics: colonisation; succession; competition; and nutrient-cycling.
Human influences*
Animal husbandry, cutting, burning, mowing, draining, irrigation,
culling, hunting, excavations, maintenance dredging, earth shaping, ploughing,
seeding,
planting, cropping, fertilising, pollution and contamination, use of
pesticides and herbicides, introduction of exotics, weeds and genetically
modified
organisms and disturbance from public access and recreation, pets and transport.
Historical context
Natural range of variation over recorded historical period.
Irregular perturbations beyond normal range (such as very infrequent
storm events).
Ecological relationships
Food webs, predator-prey relationships, herbivore-plant relationships,
herbivore-carnivore relationships, adaptation, and dynamism.
Ecological role or function
Decomposer, primary producer, herbivore, parasite,
predator, keystone species.
Ecosystem properties
Fragility and stability, carrying capacity and limiting factors, productivity,
community dynamics.
Connectivity.
Source/sink.
Numbers in a population or meta-population, minimum viable populations.
Sex and age ratios.
Patchiness and degree of fragmentation.
*Note: Many of our semi-natural habitats and wild species
have co-evolved with humans over many centuries and are adapted to traditional
cultural management practices that now sustain their current conservation
status.
(Derived from Oxford 2001)11
4.12 It is important to consider the likelihood that a change/activity will occur as predicted and also the degree of confidence in the assessment of the impact on ecological structure and function. The limitations to certainty should be described and the consequences for confidence in predictions must be stated clearly. A qualitative description may be adequate, though an objectively defined scale defined according to a stated convention is probably more helpful, and can be used even if the decision as to confidence level can only be based on expert judgement, rather than frequency data, as long as this limitation is stated. Hence, a scale that is meaningful in normal language might be: Certain, Probable, Unlikely. Alternatively, based on the fact that the 5% confidence level is conventionally chosen as the lowest limit for acceptable statistical significance in common scientific practice, a four-point scale that could be usefully employed is:
4.13 The reason for including a confidence level category of 'extremely unlikely' is that some effects may be very improbable, but extremely serious should they occur and hence merit contingency planning. Where doubt exists as to which of two categories of probability best fits the level of professional confidence, the more conservative level should be cited.
4.14 In some cases, ongoing survey or monitoring may be required to refine predictions or activate mitigation proposals.
4.15 When describing changes/activities and impacts on ecosystem structure and function, reference should be made to the following parameters, which are discussed below:
4.16 Is the impact likely to be positive or negative? Positive impacts merit just as much consideration as negative ones, as international, national and local policies increasingly press for projects to deliver positive biodiversity outcomes.
4.17 Magnitude refers to the 'size' or 'amount' of an impact, determined on a quantitative basis if possible. For example: a likely increase of three in the number of otters killed per year on a road; a total loss of the structure and function of semi-natural grassland replaced by tarmac; a partial loss of the structure and function of grassland subject to increased risk of wind-blown biocide. Whilst it may not be possible to provide a quantitative assessment in the latter example, application of some of the following parameters will provide a more accurate understanding of the likely impact.
4.18 The extent of an impact is the area over which the impact occurs. When the receptor being considered is the habitat itself, magnitude and extent may be synonymous.
4.19 The time for which the impact is expected to last prior to recovery or replacement of the resource or feature. This should be defined in relation to ecological characteristics (for example species lifecycles) rather than human timeframes. For example, five years, which might seem short-term in the human context or that of any other long-lived species, would span at least five generations of dragonflies.
4.20 The duration of an activity may differ from the duration of the resulting impact caused by the activity. For example, if short-term construction activities cause disturbance to birds during their breeding period, there may be longer-term implications due to a failure to reproduce in the disturbed area during that season.
4.21 For the purposes of this guidance, an irreversible (permanent) impact is one from which recovery is not possible within a reasonable timescale or for which there is no reasonable chance of action being taken to reverse it. A reversible (temporary) impact is one from which spontaneous recovery is possible or for which effective mitigation is both possible and an enforceable commitment has been made.
4.22 In some instances, the same activity may cause both irreversible and reversible impacts. For example, consider two of the potential impacts arising from the placement of a temporary access through an ancient wood that is subsequently allowed to grow over. The change experienced by common woodland birds of the loss of food and shelter in the woodland edge may be reversible in as little as ten years, as these resources will be replaced once the access route has grown over. Many birds are sufficiently mobile and adaptable to accommodate this change with no significant impact on populations. But, the impact on ground flora along the route of the access may be irreversible (or effectively so) if the fragile woodland soils on which they depend have been compacted.
4.23 Some changes may only cause an impact if they happen to coincide with critical life-stages or seasons (for example, the bird nesting season). This may be avoided by careful scheduling of the relevant activities, e.g. by the implementation of an EAP that specifies important constraints in relation to the timing of works.
4.24 The frequency of an activity and hence the resulting impact should also be considered. For example, there may be occasions when a single person walking a dog will have very limited effect on nearby waders using wetland habitat. However, if numerous walkers subject the waders to frequent disturbance, then feeding success may be significantly reduced. In extreme cases the birds could be permanently displaced.
4.25 In order to characterise the likely change and impact, it is necessary to take into account all the above parameters. An illustration of this is given below:
e.g. The operational phase of a temporary access road through a wood will create an increase in noise. An assemblage of breeding woodland-edge birds, in 5 ha of quality breeding habitat within a distance of 5 km from the road, will experience an increase on average, of 20 decibels of noise for three hours per day for two breeding seasons.
Confidence in describing these changes is high, based on information from the engineers and the noise and traffic assessments. However, the impact on the breeding success of the birds is less certain, as the response of all species to increased noise levels is not fully understood. From reference to published research, it is probable that the assemblage of breeding birds will change in composition, as the more susceptible species within the assemblage will fail to breed in the zone of influence during the operational period, but others will continue to breed and some may be more successful than usual, by taking advantage of the spare resources not employed by the susceptible species. As there is alternative suitable breeding habitat contiguous with the zone of influence, it is likely that the susceptible birds will move back in after the temporary access is removed, although it may be several generations before the assemblage resembles its baseline condition.
4.26 Box 13 gives an example of the way in which setting the baseline enables
effective assessment of cumulative effects.
Box 13: Example scenario for setting the baseline and assessment of cumulative impacts
The scenario
An EIA is being carried out for a proposed extension to an existing port
facility within an estuary. The extension will involve the removal of an
area of inter-tidal mud and dredging of sub-tidal mud, both areas are out
with, but adjoin, an SSSI. Expansion of another port in the same estuary
is currently underway.
Analysis
The approach to setting the baseline and considering cumulative impacts should
be agreed after discussion between the competent authority, the statutory
nature conservation agency and any other relevant agencies. It is likely
to include consideration of the following:
Predicting the Baseline
Considering cumulative impacts
The changes arising from the new project should be described in the context of the predicted baseline e.g. the current port expansion project is likely to include a capital dredge, which, together with environmental trends and predicted (but yet to occur) effects from completed projects, will change the estuary morphology. This predicted situation is the baseline, against which any changes arising from the capital dredge for the new project should be assessed, such as changes to the hydraulic processes that act on the inter-tidal habitats of the SSSI.
4.27 Legislation and policy guidance often require significant negative or positive impacts to be distinguished from others, although there is little guidance on how this distinction should be made. In this guidance an ecologically significant impact is defined as an impact (negative or positive) on the integrity of a defined site or ecosystem and/or the conservation status of habitats or species within a given geographical area. These terms are defined below in paragraphs 4.34 - 4.45.
4.28 The value of any feature that will be significantly affected is then used to identify the geographical scale at which the impact is significant. This value relates directly to the consequences, in terms of legislation, policy and/or development control at the appropriate level. So, a significant negative impact on a feature importance at one level would be likely to trigger related planning policies and, if permissible at all, generate the need for development control mechanisms, such as planning conditions or legal obligations, as described in those policies.
4.29 If an impact is found not to be significant at the level at which the resource or feature has been valued, it may be significant at a more local level. Thus, referring back to the example in paragraph 4.25, if the assemblage of birds represented 5% of this resource at one level, but 80% of the resource more locally, the impact is likely to be significant to the breeding birds there, even if it was not considered significant at the broader scale.
4.30 During the assessment process, it may be found that a site or ecosystem considered likely to be subject to a significant impact and therefore ‘scoped in’, is, on further investigation, unlikely to suffer a negative impact to its integrity. However, this will not preclude there being features within that site that are themselves of sufficient value to meet the threshold for the assessment and for which there is likely to be a significant effect on their conservation status. For example, whilst a particular impact may not be considered likely to have a negative effect on the integrity of an SPA, it may be found to be likely to have a significant impact on the conservation status of a population within the SPA (not a qualifying species) that is of local value
4.31 To summarise 4.28 and 4.29, if an ecological resource or feature is likely to experience a significant impact, the consequences in terms of development control, policy guidance and legislation will depend on the level at which it is valued. Significant impacts on features of ecological importance should be mitigated (or compensated for) in accordance with guidance derived from policies applied at the scale relevant to the value of the feature or resource. Any significant impacts remaining after mitigation (the residual impacts), together with an assessment of the likelihood of success in the mitigation, are the factors to be considered against legislation, policy and development control in determining the application.
4.32 There may be conditions or legal agreements attached to a consent to ensure the delivery of the proposed mitigation. The willingness of the proponent to enter into such arrangements will influence the assessment of the likelihood of success of the mitigation.
4.33 An example of how this approach might be applied in practice is given at the end of this chapter.
4.34 In order to test whether or not an impact will affect the integrity of a site or ecosystem (and is thereby significant) it is necessary to understand whether the changes arising from the proposed project are likely to move the baseline conditions at the site or ecosystem closer to, or further from, the condition which constitutes 'integrity' for that system. Advice on the use of the concept of integrity is given below.
4.35 The term 'integrity' has a long lineage in the ecological literature. The concept of 'integrity' evolved to deal with ecosystems and can be applied to sites that can reasonably be considered to represent an ecosystem.
4.36 Development control under the EC Habitats Directive and associated national regulations, relating to SACs and SPAs requires that development shall normally not be permitted when it will negatively affect the 'integrity' of such sites. In this case, a particular definition of site integrity is provided in the Government circular: biodiversity and geological conservation - statutory obligations and their impact within the planning system 67 and in the equivalent Welsh guidance (TAN 5)68 and Scottish guidance69 as follows:
'The integrity of a site is the coherence of its ecological structure and function, across its whole area, that enables it to sustain the habitat, complex of habitats and/or the levels of populations of the species for which it was classified.'
4.37 A site/ecosystem that achieves this level of coherence is considered to be at favourable condition.
4.38 To help understand this further, the components of ecological integrity of a site/ecosystem may be identified from previous published discussion (see the review by Leo and Levin 199770) and include the following:
4.39 For many sites, neither the favourable nor the baseline condition is described in these or any other terms. The ecologists contributing to the EcIA will therefore have to make their own assessments of what constitutes the baseline and favourable conditions. This should be done with reference to the extent and size of habitats and populations present at the time of the assessment, but recognising that this composition may change over time, due to natural dynamism or other influences not related to the proposed project. In certain circumstances, the potential levels of resources may also be relevant.
4.40 In order to assist ecologists to determine whether there is likely to be an effect on the integrity of a site or ecosystem, the answers to the following questions should be considered:
This should be in the light of the overall question:
4.41 It should be noted that it is very unlikely to be possible to evaluate impacts in terms of integrity without considering functions and processes acting outside a site's formal boundary, particularly where a site clearly falls within a wider ecosystem. Thus any predictions should always consider wider ecosystem processes.
4.42 Many ecosystems have a certain 'freeboard' in terms of biophysical change that can be absorbed before the fundamental ability of the site or ecosystem to support characteristic habitats or species populations is compromised. Clearly there will sometimes be an element of doubt as to whether the change is sufficient to cause such changes to condition described above. This should be reflected in confidence levels attached to the prediction. Mitigation measures may then be proposed to increase the level of confidence in that prediction, even when a negative effect on integrity is not predicted.
4.43 When assessing potential impacts on sites with international and national designations, integrity should be considered with detailed reference to the published citations and conservation strategies. Many such strategies list conservation objectives with associated 'criteria features', 'attributes', 'measures' and 'targets' against which likely changes can be assessed (see e.g. Wheeldon 200371). Similar information on the features of value and objectives for their conservation are also frequently available for SSSIs.
4.44 In cases of reasonable doubt, especially in relation to sites of European or national value, a precautionary view should always be taken, and a negative effect on integrity predicted.
4.45 For beneficial effects that may result in the creation of new sites or ecosystems, or intervention to restore degraded examples, the concept of integrity is equally applicable in that the intervention must be sufficiently robust as to sustain the new level of value created in all reasonably predictable scenarios.
4.46 It is recommended that the concept of 'conservation status' is used to determine whether an impact on a habitat or species is likely to be ecologically significant.
4.47 The EC Habitats Directive (Article 1, sections (e) and (i)) provide a helpful definition of 'conservation status' for habitats and species. This guidance uses slightly modified versions of these definitions so that evaluation of conservation status can be applied to habitats or species within any defined geographical area:
4.48 Conservation status may be evaluated for any defined study area at any defined level of ecological value. The extent of the area used in the assessment will relate to the geographical level at which the feature is considered important. See Table 1.
4.49 In some cases, (e.g. for BAP species and habitats) there may be an existing statement of the conservation status of a feature with formal objectives and targets. Most species or habitats will not be described in this way. In this case, the conservation status of each feature being assessed should be agreed between the ecologists working on the assessment during the scoping process.
4.50 When assessing potential effects on conservation status, the same reasoning should be applied as set out above in relation to integrity. The known or likely trends and variations in population size should be considered. The level of ecological resilience or is likely to exist, in terms of the quality of physical and biotic conditions, that would permit the given population of a species or area of habitat to continue to exist at a given level, or continue to increase along an existing trend, should also be estimated.
4.51 A significant positive impact could be defined as one that prevented or slowed and existing decline as much as one that permitted a population or habitat area to increase.
4.52 There are a number of approaches for determining significance in current use. Most typically, significance is defined using a matrix in which ecological value and magnitude of impact are combined to determine different grades of significance, for example in Transport Analysis Guidance.
4.53 Using a wholly subjective link between value and 'magnitude', matrices generally assign different levels of significance to various cells in the matrix. Decision-makers using the results from such a matrix then have to distinguish between, for example, an impact of ‘medium significance’ against one of 'low significance' without any guidance other than an intuitive understanding of these terms which are inevitably subject to individual interpretation.
4.54 This type of matrix tends to always place negative impacts on a feature of local value into a 'low' significance category. This can downplay local values for biodiversity. A check should be made of planning policies to ascertain whether special provisions have been made for protecting such resources (e.g. in London there is a Local grade of nature conservation site below Borough Grade II level).
4.55 A worked example considers the changes affecting a Cetti's warbler Cettia cetti population (five breeding pairs) in the event of a road-widening scheme. Where possible these changes are measured and their impacts on the population are characterised by reference to the key aspects of the ecosystem upon which the birds rely. The likely effect on the conservation status of the population is then considered with reference to current status and conservation objectives to determine whether the impacts are significant or not.
4.56 A commentary provides the background to the analysis of the overall significance on integrity and conservation status of feature (that might be suitable for the main text of the ES), with a Table giving a summary of the analysis.
Note
The worked example provided below, whilst intended to be as realistic as
possible, is fictitious and for illustrative purposes only. Its aim is to
show the general principles of how the approach to EcIA recommended in these
Guidelines might be applied in practice. The actual values of various parameters
and the conclusions reached could differ in a real situation; other parameters
could be relevant and other research findings brought to bear.
The hypothetical road scheme in question is the widening of a two-lane A road (c. 18.5 m wide) into a dual carriageway with hard shoulders (final hard surface increase to c. 34 m). This scheme is being implemented largely to take traffic out of the centre of a country town. All the widening in the stretch under consideration would take place to the east of the existing road necessitating the removal of improved grassland in this location. The scheme is located within the county of Cymrent in the west of the UK. The road in the area under consideration runs due north-south. Once commissioned, the scheme would permit an almost three-fold increase in traffic volume from 9,500 to an estimated 28,000 vehicles per day and an increase in average speed from 80 kph to 100 kph (c. 50 mph to 60 mph). Site clearance would result in construction noise over six weeks. Construction activity would last eight months.
'Acquire land, compulsorily or by agreement, for the purpose of mitigating any adverse effect which the existence or use of a highway constructed or improved by a Highway Authority has or will have on the surroundings of the highway.'
Mitigation under these powers, however, does not include compulsory land purchase for the purposes of net ecological enhancement. Highways Authorities also have the duties of ensuring the wise spending of public money and that roads are safe.
1.1 Proposed activity, duration of activity, biophysical change and relevance
to receptor in terms of ecosystem structure and function
Site clearance and construction activities would result in increased noise
over eight months. Ambient noise level increases would be variable, but at
times there could be considerable increases in noise levels. This would change
the noise environment within and near bird territories, creating the potential
for impact on the audibility of territorial song and an increase in general
stress levels, and hence possible adverse effects on the ability of birds
to hold territories and breed successfully.
1.2 Characterisation of unmitigated
impact on the feature
If works were to take place within the breeding season, there would be a
negative impact, probably extending c. 500 m from the road and affecting
the whole Cetti's warbler population of 'The Cuts'. It
is not possible to quantify the magnitude of effect from the available literature.
The effect of the construction noise would last longer than the duration
of the noise and should be considered effectively permanent through the construction
period. The duration of effect would be just one breeding season, but abandonment
could conceivably be permanent for some individuals. Nevertheless, the effect
would probably be reversible in time, once construction was over.
1.3 Rationale
for prediction of effect on integrity (of a site or ecosystem) or conservation
status (of a habitat or population)
The effects of such variable noise disturbance on breeding of both Cetti's
warblers in particular, and birds in general, at different distances from
the source of disturbance, are very little understood. Even though the Cetti's
warbler song is particularly loud, clarity or individual recognition ability
might be lost against background noise. It is also possible that construction
noise might cause increased general stress (Reijnen et al. 2002), if
not site abandonment. Cetti's warbler is very susceptible to cold weather
and a small population could be wiped out in a severe winter especially if
already 'stressed'. On a precautionary basis, it is considered
probable that this temporary impact could negatively affect the conservation
status of the local population.
1.4 Significance without mitigation and confidence
in assessment
A significant negative impact at the County level is probable. Such an impact,
if it occurred, would be potentially in breach of law, as the Cetti's
warbler is a Schedule 1 species and hence protected from disturbance whilst
breeding.
1.5 Mitigation, enhancement and compensation
Construction works in the stretch should avoid the breeding season as far
as possible. If this were not possible, then the only practicable means of
reducing the noise would be the installation of a permanent sound barrier
in advance of construction works.
1.6 Residual significance (confidence)
It is certain that any effect of construction outside the breeding season
would not be significant. With the sound barrier, the effect of construction
noise would be unlikely to be significant.
1.1 Proposed activity, duration of activity, biophysical change
and relevance to receptor in terms of ecosystem structure and function
Increased traffic volume and speeds in perpetuity would lead to a permanent
increase in ambient noise levels, which would penetrate further into the
Cetti's warbler habitat. This would have a potential impact on audibility
of territorial song and hence ability of birds to hold territories. This
effect, perhaps combined with increased background visual sources of potential
disturbance (car lights and movement), could increase general stress levels.
Such impacts can extend for several hundreds of metres from a road (see Reijnen et
al. 1995).
1.2 Characterisation of unmitigated impact on the feature
The result of such changes, if unmitigated, would be a negative impact on
the Cetti's warbler population in 'The Cuts'. Its extent
would probably encompass all currently viable breeding habitat for the Cetti's
warbler in 'The Cuts' (see 1.3 below). This impact would be effectively
permanent and not reversible, as noise would always be affecting the population
and require mitigation.
1.3 Rationale for prediction of effect on integrity
(of a site or ecosystem) or conservation status (of a habitat or population)
Although not specifically developed in relation to Cetti's warblers
in the UK, the best available model for predicting likely impacts in this
case is the guidance developed to predict the effects of road noise on song-birds
in Holland including warbler species (Reijnen et al. 1995). The tables in
this publication have been used to inform the present example. This Dutch
model is considered likely to be applicable as the road in question meets
all of the criteria set by the model. The distance from the road at which
no effect on songbirds in fairly open habitat (<30% woodland) generally
would be expected to occur with mean traffic speeds of 80 kph (50 mph) and
9,500 vehicles per day, would be around 185 m (Reijnen et al. 1995
Table 2). The local population of Cetti's warblers in 'The Cuts' should
accordingly be assumed (on a precautionary basis) to be already somewhat
compromised and/or limited by the availability of habitat that is free from
road-related disturbance. Such disturbance probably applies to at least the
first 135 or so metres of 'The Cuts' (20%) from the western edge
(nearest the road) and might explain the relative lack of sightings of Cetti's
warblers reported by the local Wildlife Trust from this band of 'The
Cuts'. With the increase in traffic volume to 28,000 vehicles per day
and speed to 100 kph (60 mph), this effect distance could increase by over
300%, to at least 565 m (Reijnen et al. 1995 Table 5, that is, 580
m from original A road edge, as the dual carriageway is c. 15 m wider). This
predicted
effect zone would, therefore, encompass the whole area of 'The Cuts' containing
habitat currently suitable for Cetti's warbler. It is certain that
these biophysical changes would decrease the quality of the breeding habitat.
The Cetti's warblers might relocate their breeding locations to other
parts of 'The Cuts', in which case territories would be smaller and possibly
extend into less suitable habitats, negatively affecting fitness is probable
that it would lead to site abandonment by several pairs (based on the average
reductions noted by Reijnen et al. 1995, p.33, loss of at least 2 to 3 pairs
is probable). Accordingly, it is considered probable that the conservation
status of Cetti's warbler in 'The Cuts' would be negatively
affected.
1.4 Significance without mitigation and confidence in assessment
A significant negative impact at the County level is certain. Such an impact,
if it occurred, would be potentially in breach of law, as the Cetti's
warbler is a Schedule 1 species and hence protected from disturbance whilst
breeding.
1.5 Mitigation, enhancement and compensation
Policy and the legal requirement to avoid intentional or reckless disturbance
to a Schedule 1 bird clearly indicate a need to mitigate fully for this impact.
Two measures are proposed to achieve this:
1.6
Residual significance (confidence)
It is probable that there would be a short-term, (c. 5 years) negative impact
on the Cetti's warblers, significant at the County level until maturation
of the mitigation measures with respect to habitat. However, in the long-term,
it is probable that full mitigation would be achieved and the value of the
feature be returned to County level and it is probable that there would be
no
residual impact of significance on the Cetti's warbler population in 'The
Cuts' in relation to this biophysical change.
1.1 Proposed activity, duration of activity, biophysical change and relevance
to receptor in terms of ecosystem structure and function
The scheme would result in > 50% physical increase in any barrier effect
that the road might already be exerting on dispersal of adults and/or post-breeding
dispersal of juveniles. This is especially the case given the presence of
another known population of Cetti's warblers 500 m west of the A road
out with the CWS. There would also be an increase in collision risk due to
increased traffic speeds, and perhaps volumes (though increased traffic volumes
can actually increase the deterrent for crossing the road and hence actually
reduce collision risk).
1.2 Characterisation of unmitigated impact on the
feature
The biophysical change would exert a permanent adverse effect on the whole
local population of Cetti's warblers in 'The Cuts' and
would be in practical terms irreversible (though compensation would be feasible).
1.3
Rationale for prediction of effect on integrity (of a site or ecosystem)
or conservation status (of a habitat or population)
It is considered probable that the existing A road is already acting to an
extent as a deterrent to post-breeding or post-fledging dispersal of some
individuals, and this effect might increase with the > 50% increase in
width of the barrier and higher vehicular speeds. There are no means of quantifying
this possible impact based on existing scientific knowledge. Any reduced
dispersal could result in reduced genetic interchange between populations
and increase the risk of genetic isolation and inbreeding depression. It
is also the case that any individuals dispersing across the road would be
exposed to a higher risk of collision with vehicles. This additional risk
is also currently unquantifiable, but any adult mortality (or substantial
juvenile mortality) in such a small population could notably increase local
extinction risk. It is concluded that both the increased barrier effect of
the nearby road and the increased collision hazard would probably negatively
affect the conservation status of the Cetti's warblers in 'The
Cuts'.
1.4 Significance without mitigation and confidence in assessment
It is considered probable that there would be a negative effect, significant
at the County level.
1.5 Mitigation, enhancement and compensation
The potential impact cannot be confidently mitigated because 'green crossings'
over roads are expensive and their likely success in attracting Cetti's warblers
to cross safely rather than through the traffic stream is not possible to
quantify from previous studies. Nevertheless, compensation should be feasible
by increasing the potential for population growth in other places in Cymrent.
The County BAP has identified a strategy to achieve this, which includes
the provision of a grant for land-owners to encourage them to manage existing
habitats, or create new habitats for Cetti's warblers. An appropriate contribution
to this grant fund would be made by the Highway Authority, were the scheme
to be approved.
1.6 Residual
significance (confidence)
It is considered probable that the population of Cetti's warblers in 'The
Cuts' might experience a permanent loss of conservation status, which
would constitute a significant negative impact at the County level. However,
it is probable that the proposed compensation would, in the longer term,
increase the chances of success of a county-wide population enhancement strategy,
resulting in no significant residual effect on Cetti's warblers in
the county as a whole.
Linked to these mitigation proposals there would be a requirement for monitoring of the success of the mitigation in keeping with legal requirements. It is likely that the Highways Authority in this instance would monitor the growth and maturation of the proposed tree belt and arrange separate monitoring of the Cetti’s warbler population, in this case almost certainly through the local Wildlife Trust.
Table 1: Summary Impact Table
| Proposed Activity | Characterisation of unmitigated impact on the feature | Significance without mitigation and confidence level | Mitigation and Enhancement | Residual significance and confidence level |
| Construction Impacts | ||||
| Site clearance and construction | If construction took place in the breeding season there would be a negative impact (variable over the day/night cycle, but effectively constant) extending up to 500 m from the road and affecting c. 80% of the local population to varying extents over one breeding season. It is not possible to quantify the magnitude of this, but it is likely to be reversible after the end of construction. | Negative effect on conservation status:
probable. Therefore, significant negative impact at the County level: probable. |
Option 1: Avoidance of construction in the breeding season. Option 2: Construction of permanent sound barrier in advance (see below). |
Option 1: Certain not to have a negative effect on conservation status therefore not significant Option 2: Tried and tested engineering technique. Unlikely to have a negative effect on conservation status, therefore unlikely to be significant at the County level. |
| Operational Impacts | ||||
| Increased background noise due to increased traffic volume and speed. | Although there would be some year-round and night to day variation in levels of noise, the overall negative effect would be permanent. The extent would probably be at least 400 m beyond the current limit of effect of the existing road. This would not be reversible as noise will always be affecting the population without mitigation. | Negative effect on conservation status: certain.
Therefore, significant negative impact at the County level: certain. |
Combination of woodland buffer planting (or planting plus sound barrier), plus restoration of eastern part of the CWS to support Cetti's warblers | Probable negative effect significant
at the County level in the short-term (c. 5 years).
Probable that effect on local population and at the County level in the long-term not significant. |
| Increased barrier effect and collision risk | The effect on dispersal ability due to increased road width, higher vehicular speeds and collisions would have a probable negative impact on the local Cetti's Warbler population and would be effectively permanent, though compensation should be feasible. | Negative effect on the conservation status: probable.
Therefore, significant negative impact at the County level: probable. |
Cannot be readily mitigated.
Compensation proposed by financial contribution to implementation of County BAP for the species. |
Probable significant negative impact
at the County level.
With compensation probable that not significant in the long-term. |
| Overall Significance of Effect | Without mitigation:
Negative effect at the County level significant. |
If all mitigation/enhancement undertaken: Negative effect at the County level in the medium term: significant. Negative effect at the County level in the longer term: not significant. |
||
Reijnen, M.J.S.M., Veenbaas, G. and Foppen, R.P.B. 1995. Predicting the Effects of Motorway Traffic on Breeding Bird Populations. Ministry of Transport and Public Works, Directorate General for Public Works and Water Management, Road and Hydraulic Engineering Division; DLO - Institute for Forestry and Nature Research, Rijkswaterstaat.
Reijnen, R., Foppen , R. F., Veenbaas, G. & Bussink, H. 2002. Disturbance by Traffic as a Threat to Breeding Birds: Valuation of the Effect and Considerations in Planning and Managing Road Corridors. In: B. Sherwood, D. Cutler and J. Burton (Eds.) Wildlife and Roads: The Ecological Impact. Imperial College Press, London.
Snow, D. and Perrins, C. 2000. The Complete Birds of the Western Palaearctic on CD-rom. Oxford University Press.
c Guidance on SEAs and biodiversity can be found in Strategic Environmental Assessment and Biodiversity: Guidance for Practitioners(June 2004)
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