Nature, landscape and biodiversity

Habitat defragmentation measures for infrastructure, 2018

At the end of 2018, of the 176 ecological barriers identified and selected in the Multiyear Habitat Defragmentation Programme, 126 had been removed and 40 partly removed by taking mitigation measures, such as the construction of wildlife passages. After 2018 a further 28 barriers will be removed, while 22 barriers will not be removed because the proposed measures proved not to be feasible. As of 2017 there were almost 2,100 wildlife crossings on motorways and provincial roads.

About two-thirds of ecological barriers caused by national transport infrastructure removed

The multi-year habitat defragmentation programme (Meerjarenprogramma Ontsnippering - MJPO) (VenW 2004), which was introduced in 2005, aims to remove the ecological barrier effects in the national ecological network caused by national transport infrastructure: roads, waterways and railways. Rijkswaterstaat (the government agency responsible for the construction and maintenance of the country's main infrastructure facilities) and ProRail (the rail network operator) are responsible for implementing the MJPO for the national government, under the direction of the provincial authorities. At the end of 2018, of the 176 identified ecological barriers, 126 had been completely removed and 40 partially removed (MJPO 2019). 'Completely removed' means that all the necessary measures have been taken to remove the barrier effect; 'partially removed' means that some measures have been taken, but not all those that are needed to completely remove the barrier effect.

Removing ecological barriers involves measures such as building green bridges, eco-culverts, wildlife underpasses, wildlife overpasses at tree crown level and hop-overs ('defragmentation'). In many cases it is possible to adapt existing bridges and viaducts to make them suitable for use by wildlife. Tried and tested methods include guiding animals by erecting fences and planting bushes, and introducing rows or low 'walls' of stumps and branches in culverts to provide a suitable micro-environment passageway for small animals. However, removing some barrier effects may require the construction of several wildlife crossings because they stretch across several kilometres or consists of multiple obstacles.

Habitat defragmentation measures since the 1970s

Wildlife crossings have been built across motorways and provincial roads since the 1970s. In 1974 the then Ministry of Transport, Public Works and Water Management started building badger tunnels under motorways. In 1988 two large green bridges (wildlife overpasses) were built over the A50 motorway in the Veluwe region. By 2005 about 440 wildlife crossing structures had been built on motorways and about 1,100 on provincial roads. Most of the wildlife crossings built since 2005 were incorporated into new road construction projects. At the moment there are 661 wildlife crossings on motorways and more than 1,400 on provincial roads. Smaller wildlife crossing structures are also built by municipal councils and nature conservation organisations to remove local barrier effects. As there is no national record of wildlife crossings resulting from such local initiatives, they are not included in this indicator.

Revised target adopted in 2015 in view of new boundaries of the national ecological network

When the MJPO began there were 215 identified ecological barriers, based on the policy objectives for the national ecological network. Following a revision of the national ecological network in 2010 most of the provinces redrew the boundaries of the network in their territories and the 'robust ecological corridors' were cancelled. In 2015 an assessment was made of the new ambitions and the remaining barriers in the former robust ecological corridors were dropped from the MJPO. The MJPO is now limited to the barriers in the former robust ecological corridors which had been completely removed before December 2015 and the barriers in the current national ecological network that have been removed or are due to be removed under the budget provided by the Ministry of Infrastructure and the Environment. An additional 2 barriers have been dropped from the list because further research has shown that no measures need to be taken. The MJPO now covers 176 barriers.

Achieving the 2018 targets

When the MJPO programme came to an end in 2018 a total of 126 ecological barriers had been removed. This is 72% of the revised target of 176 barriers. Of the remaining 50 barriers, 28 will be completely removed by incorporating the necessary wildlife crossing structures into major infrastructure projects yet to be completed. A further 22 barriers will not be completely removed and will continue to present ecological barriers because a number of proposed measures have proved not to be feasible. Measures are considered not to be feasible when they do not meet the required safety or technical standards, are not cost-effective enough or the required cooperation of local stakeholders cannot be guaranteed.

Why take measures to mitigate habitat fragmentation?

In smaller isolated habitat patches where the exchange of individuals with other areas is restricted or impossible, populations of plants and animals may become too small to remain viable because the area of habitat is insufficient. The chance of extinction in these areas increases if, for example, food supply decreases due to extreme weather conditions. If a species disappears from such an isolated area of habitat, it will not be able to recolonise it when conditions become favourable again. For species to survive over the long term, therefore, it is essential that individuals are able to disperse and disperse between habitat patches. Climate change makes it even more important for individuals of a species to be able to disperse between different habitat patches.

Many species are on the Red List because the habitats on which they depend have become too small and/or isolated. In the Netherlands habitat fragmentation is often caused by roads, but fences and noise barriers can also present unsurmountable barriers. Species such as badgers, foxes, deer, frogs and even some birds, bats and insects have great difficulty in crossing roads, or may be unable to do so at all, which prevents them from moving through the landscape. This can result in patches of species habitats becoming isolated. Even if the individuals of a species are physically capable of crossing a barrier, they may be killed by vehicles or avoid the road altogether and adapt their use of the habitat. The barrier effect of roads therefore inhibits exchange between animal populations. The construction of wildlife crossings allows animals to disperse between areas of habitat. When there is sufficient exchange between areas, a species will have a greater chance of survival.

Use and effectiveness of wildlife crossings

Surveys show that most wildlife crossings are used by several species. It has now been demonstrated that wildlife crossings - in combination with wildlife fencing - can considerably reduce road mortality. These crossings have also allowed some species to expand their range or recolonise areas of habitat. It is not known exactly what effect wildlife crossings have on the viability of animal populations, but model calculations show that in many places wildlife crossings are essential for the long-term survival of some species populations. At the moment, though, few studies have been done that demonstrate this in the field as well.

Policy objectives for the national ecological network

A precondition for the sustainable conservation of biodiversity is ecological connectivity to allow plant and animal species to disperse between habitat patches. Biodiversity conservation is an important goal of the Convention on Biological Diversity (CBD) as well as the EU Birds and Habitats Directives and the EU Biodiversity Strategy. The Netherlands is committed to the objectives of the CBD and the Birds and Habitats Directives (Natura 2000).

The Dutch national ecological network was introduced in the 1990 Nature Policy Plan by the then Ministry of Agriculture, Nature and Food Quality. The aim of this network is to halt the decline in the area of natural habitat and biodiversity (Natuurareaal op het land 1900-2012) through the creation of a coherent network of protected areas. This is being achieved by increasing the size of protected areas (Gebiedsgrootte natuurgebieden op het land, 1990-2019) and connecting them by creating wildlife crossings (this indicator) so that more species can find suitable habitats and the long-term viability of many species populations can be ensured (Geschiktheid ruimtelijke condities landnatuur, 2019). Large natural areas also help to restore natural water tables and improve water quality and environmental conditions (Milieucondities in water en natuurgebieden, 1990 - 2014). Areas of natural habitat are increased in size and connected by acquiring surrounding agricultural land and agricultural enclaves and creating new habitats on this acquired land, followed by conservation management (Realisatie Natuurnetwerk - verwerving en inrichting, 1990-2018). In 2013 an agreement (Nature Pact) was made between national government and the provincial authorities on nature policy and the realisation of the national ecological network. The responsibility for the creation and management of the network has been delegated to the provinces and is a core element in the government's vision for 'robust natural areas'.

References

Relevant information

Archive for this indicator

Reference for this page

CBS, PBL, RIVM, WUR (2021). Habitat defragmentation measures for infrastructure, 2018 (indicator 2051, version 13 , 11 November 2021 ). www.environmentaldata.nl. Statistics Netherlands (CBS), The Hague; PBL Netherlands Environmental Assessment Agency, The Hague; RIVM National Institute for Public Health and the Environment, Bilthoven; and Wageningen University and Research, Wageningen.

The Environmental Data Compendium is a partnership of CBS, PBL, RIVM and WUR.