Onshore: potential effects

AuthorDirectorate-General for Environment (European Commission)
54 Guidance on Wind Energy Developments and EU Nature Legislation
Guidance on Wind Energy Developm ents and EU Nature Legislation
5.1 Introduction
5.1.1 Types of impacts
This chapter reviews the main types of impacts from onshore wind energy development projects. Such impacts could have
significant effects on habitats and species protected under the Habitats and Birds Directives.
The purpose of this chapter is to provide developers, NGOs, consultants and competent national authorities with an
overview of the potential impacts for different receptor groups of EU-protected habitats and species. These impacts should
be considered when developing or reviewing an onshore wind energy plan or project. However, as the identification of
likely significant effects is always case-specific, the real effect of a wind energy development project on EU-protected
species and habitats will be highly variable. There are clearly many cases where well-designed and appropriately sited
developments have no likely significant effect, while other cases may give rise to several likely significant effects.
It is widely recognised that switching to renewable energy benefits global biodiversity in a way that is relatively
straightforward to assess. However, the local interaction between a particular wind energy development and EU-protected
habitats and species tends to be more complex and uncertain. For this reason, it is essential to examine each plan or
project on a case-by-case basis. Ultimately, each assessment should be ‘at a level of detail proportionate to the risks and
probable effects and the likely importance, vulnerability, and irreplaceability of affected biodiversity’ (Brownlie & Treweek,
Effects from onshore wind energy developments may arise in one or more of the five typical phases of wind energy
pre-construction (e.g. meteorological equipment, land clearance)
construction (construction of access roads, platform, turbine, etc. and transport of material)
operation (including maintenance)
repowering (adapting the number, typology and/or configuration of turbines in an existing wind farm)
decommissioning (removing the wind farm or individual turbines).
It is worth noting that the potential impact of repowering may be different to that of the original project. For example, using
larger turbines can increase the collision risk window (i.e. by increasing the total rotor swept area), but at the same time
reduce turbine rotation speed. This could result in the risk of collision shifting from one receptor group sensitive to changes
in turbine rotation speed (e.g. large birds of prey) to a receptor sensitive to total rotor swept area (e.g. bats).
When assessing t he likely significant effects of onshore wind energy developments on EU-protected habitats and species,
it is important to bear in mind that such effects may arise from the entire project footprint, i.e. not just from the wind turbines
themselves but also from associated infrastructure. For example, we may see an impact caused by access roads, site
access (e.g. for maintenance works or during construction), anemometer masts, construction compounds, foundations,
temporary contractors’ facilities, overhead and underground electrical connections for access to the grid, spoils, and/or any
sub-station, control building, etc.
Potential impacts may be temporary or permanent. They may result from activities within or outside Natura 2000 site
boundaries. In the case of mobile species, these potentially affect individuals well away from associated Natura 2000 sites.
For example, a site may be designated because there are hibernating bats that breed at some distance away; mortality of
those breeding individuals would affect the site’s population. Potential effects may arise from the plan or project alone and
may occur at different times during the project life-cycle. Plans and projects acting in combination to produce cumulative
effects are of growing importance, as wind energy is expanding to meet renewable energy targets.
In the next subchapters, the types of impacts are described for each of the major receptor groups. An overview is given in
Table 5-1. The description is based on an extensive literature review. Although there are still many uncertainties, in
particular in the context of innovative technologies and mitigation measures, insights are growing rapidly, often thanks to
an increased and improved monitoring; over the next few years much more interesting findings are expected to become
Guidance on Wind Energy Developments and EU Nature Legislation 55
Guidance on Wind Energy Developm ents and EU Nature Legislation
Table 5-1 Overview of impacts of onshore wind energy developments
Impacts of onshore wind energy
Habitat loss and degradation
Habitat fragmentation
Habitat disturbance
Introduction of invasive alien species (IAS) during construction (soils contaminated with
seeds from IAS)
Habitat creation (habitat creation away from the wind farm to attract birds to these habitats
and lead them away from the wind farm; habitat creation in intensively managed farmland
by providing less intensively used residual areas)
Changes in microclimate
Soil compaction
Indirect effects
Habitat loss and degradation
Disturbance and displacement
Habitat fragmentation
Barrier effect
Barotrauma (i.e. damage to body tissues caused by a difference in pressure)
Loss or shifting of flight corridors and roost sites
Increased availability of invertebrate prey, and thus increased collision risk, due to night
Indirect effects
Habitat loss and degradation
Disturbance and displacement
Habitat fragmentation
Barrier effect
Indirect effects
Other species
Habitat loss and degradation
Habitat fragmentation
Disturbance and displacement
Indirect effects
5.1.2 Mitigation measures
After consideration of the types of impacts listed above, each sub-chapter describes possible mit igation measures to avoid
or reduce the likely significant effects73.
Mitigation measures are very important in impact assessments. If adverse impacts on the site’s integrity have been
identified during the appropriate assessment or cannot be ruled out, the plan or project in question cannot be approved.
However, depending on the degree of impact identified, it may be possible to introduce certain mitigation measures that
will avoid these impacts or reduce them to a level where they will no longer adversely affect the integrity of the site.
Mitigation measures must be directly linked to the likely impacts identified in the appropriate assessment and can only be
drawn up once these impacts have been fully assessed and described in the appropriate assessment. Thus, mitigation
measures can only be considered at this stage and not at the screening stage.
The identification of mitigation measures, like the impact assessment itself, must be based on a sound understanding
of the species and habitats concerned.
Mitigation measures to avoid or reduce impacts or prevent them from happening in the first place must not be confused
with compensatory measures, which are intended to compensate for any damage the project may cause.
Compensatory measures can only be considered under Article 6(4) if the plan or project has been accepted as
necessary for imperative reasons of overriding public interest and where no alternatives exist.
Mitigation measures may be proposed by the plan or project proponent and/or required or imposed by the competent
national authorities. In practice, the need for mitigation measures is often acknowledged at an early stage in a plan/project’s
design or inception stages, for example through a ‘pre-application’ discussion between the developer/applicant and the
73 Another category are what are called ‘accompanying measures’. These are additional to regulatory measures of
avoidance, reduction and compensation, and aim, for example, to improve knowledge on habitats or species or to carry
out research projects. This is covered in Chapter 3.6 on stakeholder engagement and in particular in Case study 3-5 and
Case study 3-6; it is not the focus of Chapter 4.2.
56 Guidance on Wind Energy Developments and EU Nature Legislation
nature conservation advisers. In such cases, the need for mitigation measures is included as part of the application for
authorisation (see also good practice Case study 3-6).
Mitigation measures should consider:
avoidance: preventing significant impacts from happening in the first place
reduction: reducing the magnitude and/or likelihood of an impact.
Table 5-2 provides an overview of potential mitigation measures in relation to a wind energy development’s planning and
design stages and five life-cycle phases.
Table 5-2 Types of mitigation measures (adapted from Gartman, 2016)
Measure (type)
Planning, siting and design
Macro-siting (avoidance)
This relates to the spatial planning of wind energy developments and ensures their
appropriate siting from a conservation perspective. Avoiding ecologically sensitive
areas (supported by, for example, wildlife sensitivity mapping) is a key avoidance
Configuration of wind farm: choosing the type of turbines and their exact position74
Infrastructure design (reduction)
Turbine number and technical specifications (including turbine height, lighting,
cable burial depth and shielding, foundation design, etc.)
Avoiding, reducing or phasing activities during ecologically sensitive periods
Alternative construction methods
and barriers (reduction)
Avoiding or reducing potentially disturbing or harmful visual stimuli and emissions
such as noise and vibration
Avoiding, reducing or phasing activities during ecologically sensitive periods
Alternative construction methods
and barriers (reduction)
Avoiding or reducing potentially disturbing or harmful visual stimuli and emissions
such as noise and vibration
Deterrents (reduction)
Acoustic and visual methods
Timing of turbine operation
Curtailment of turbine, turbine blade feathering and increasing cut-in speeds75
(e.g. stopping turbine rotation when migratory birds are approaching at turbine
height, or reducing the time that turbines are rotating)
Deterrents (reduction)
Acoustic, visual and electromagnetic measures
Rewilding access roads and/or
discourage use of access roads
Once the turbines are constructed, large access roads no longer have any function
(as maintenance staff can use smaller roads). Therefore they can be temporarily
rewilded (until the repowering or decommissioning phase) and barriers can be
installed to prevent access by non-authorised persons.
Habitat management (reduction)
Habitat management can have different applications. One approach is to make
habitats unattractive in the vicinity of turbines (e.g. creating (un)attractive foraging
or breeding habitats and removing carcasses to keep raptors away) combined with
creating attractive habitats away from the ‘risk zone’ (e.g. away from areas where
there is a collision risk), with the aim to dissuade and lure species away from
turbines. Another approach is to create some form of biodiversity near the
turbines, in particular when these are located in intensive farmland areas. This
needs to be considered case by case.
Dismantling and relocating
Replacing (e.g. with higher and fewer turbines) or repositioning turbines
Avoiding, reducing or phasing activities during ecologically sensitive periods
Alternative construction methods
and barriers (reduction)
Avoiding or reducing potentially disturbing or harmful emissions such as noise,
vibration and electromagnetic fields
74 The arrangement and position of turbines has a significant influence on the location of associated infrastructure; micro
siting should be considered in a way that takes into account all relevant factors.
75 Blade feathering is the process of changing the angle (pitch) to reduce rotation. Cut-in speed is the speed at which a
turbine starts to rotate and generate electricity.

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