Compensatory measures have to be taken:

• If a development is foreseen to have significant impacts on areas that are protected by the EU Birds and Habitat Directives (this is the case in all EU member states) or by national regulations (this is the case in Germany and Switzerland).
• If a development is foreseen to have impacts on areas of high conservation value on which a non-legislative compensation policy is operative.

See also Chapter 5 which defines criteria where ecological impacts require mitigation measures.

• The developer is responsible for implementing the ecological compensation principle.
• As a result of this, the developer provides funds to achieve compensatory measures, and to monitor and modify them if results are unsatisfactory.

Several European countries have experience with habitat creation. It usually involves the conversion of farmland into habitats with increased nature qualities. The process includes:

• Land acquisition (or management agreements).
• Specific design (e.g. soil manipulation, adjusting the water table).
• Management planting of selected species e.g. hay meadow species or woodland species, fertilizer management, time of cutting etc.
• Monitoring and aftercare.

Sometimes habitat creation may be accompanied by translocation, i.e. soil and/or species being removed from the impacted (donor) site to the new (receptor or compensation) site. The receptor site must be suitable, and should contain the same soil properties as the donor site. The advantage of this technique is that the donor and receptor sites show high similarity in soil and/or target species. However, this method is expensive, and timing as well as soil conditions are critical.

Enhancement of habitat implies that the compensatory habitat is present, but not of the right quality. Former impacts may have caused habitat deterioration. Compensation may include measures needed to enhance habitat quality (such as reducing grazing pressure, raising the water table). The advantage of enhancing the quality of existing habitat is that often the soil and hydrological properties are close to those required to meet conservation objectives.

Compensation aims at a 'no net loss' situation for protected species and habitats. So compensatory measures should preferably aim at creating similar ecological qualities to the area impacted ('in-kind' compensation). However, it may be legitimate to compensate in terms of comparable qualities ('out-of-kind' compensation). This is the case when in-kind compensation is not feasible and out-of-kind compensation favours the persistence of an important species that is impacted by infrastructure developments.

Location of compensation sites can be considered as on-site or off-site compensation. Compensatory measures are best undertaken outside the impact zone of the highway but within the landscape-ecological context of the area ('on-site' compensation). If the compensation is too close to the highway, the ecological values on the compensation sites will be influenced negatively by the highway. The width of the impact zone may depend on the target species of the compensatory measures. It may be advisable to locate compensation areas away from impacted areas (off-site compensation) if this increases the chances of success or reflects availability of suitable compensatory areas.

In-kind vs. out-of-kind habitat compensation

In-kind compensation involves replacement with the same habitats, species or functions; out-ofkind compensation involves replacement with alternative habitats, species or functions.

In-kind compensation for three type of impacts:

1. Habitat loss: creation of habitat patches of the same size and quality (on-site or off-site); upgrading existing habitat may also be effective as a secondary approach.
2. Habitat degradation: upgrading habitats.
3. Habitat isolation: a combination of enlarging and upgrading habitats or increasing the connectivity of isolated habitat patches.

Examples of compensating for habitat degradation 

1. Off-site raising of groundwater levels to compensate for depressed water tables.
2. On-site/off-site raising of the water table or introducing a new management regime to render noiseaffected habitat more attractive to meadow birds.

Examples of compensation for habitat isolation

1. Closure of the 'lower-level' road network (e.g. trunk roads) to motorised traffic to compensate for highway construction.
2. Developing new patches attached spatially to or located within existing nature areas, thus forming larger units with a potentially greater number of species and individuals.
3. Developing new patches to serve as links between the core habitats of species, thus reinforcing or creating ecological corridor functions.