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Fragmentation and isolation of green spaces

Better connectivity between green spaces is an important challenge with a view to the conservation of biodiversity in the Brussels-Capital Region. The connectivity between green spaces remains a big problem for open green spaces and in the central neighbourhoods, but it is also problematic in the periphery, especially in the case of the Sonian Forest, which is a crucial area for the Brussels ecological network.

The fragmentation of natural habitats threatens biodiversity

Both at a global and local scale, the extension of the developed surface area is leading to the fragmentation of natural habitats, which results in loss of biodiversity.
The fact is that the presence and conservation of certain animal and plant species do not only depend on the availability of natural habitats of a sufficient size and quality, but also on the possibility for these species to move between the different areas, in search of food or new territories, or for reproduction or migration. The disappearance of connections between natural environments and the isolation of these environments by obstacles that are difficult – or even impossible – for the species to overcome, can have negative genetic and demographic consequences for the long-term survival of certain species. The 'barrier effect' can be due to transport infrastructure (roads, car parks, railway lines, a canal, etc.) or buildings – but also, for instance, artificial lighting. In this respect, studies about bats in the Brussels Capital Region have shown that the lighting of previously unlit roads which cross the flight paths of the bats can have serious ecological consequences.

There is a lack of connectivity between green spaces, even in areas that have become a lot greener

A map of undeveloped areas and the percentage of green cover, based on high resolution satellite images, was made in 2010 at the request of Bruxelles Environnement-Leefmilieu Brussel (see fact sheet 'Analyse van de onbebouwde oppervlakken in het BHG door interpretatie van satellietbeelden'). This shows that approximately 54% of the territory of the Region is made up of green spaces. However, these are distributed very unevenly across the Region. For instance, the percentage of green cover is considerably higher in the neighbourhoods of the second and first circles than in the central neighbourhoods. Furthermore, these green areas mainly consist of dense vegetation (forests, parks and gardens with trees and bushes). Open environments (lawns, pastures, farmland) are scarcer and mainly concentrated in the west and north of the Region.
In this study the characteristics of the fragmentation and isolation of the different green spaces in Brussels were analysed as well. The fragmentation maps included below offer an interesting view of the spatial connectivity of the green spaces in the Brussels-Capital Region. During the preparation of these maps the distance between different parcels of the same type was taken into account (open environment of more than 0.5 ha, closed/densely vegetated environment with a surface area between 0.5 and 5 ha and closed/densely vegetated environment with a surface area of more than 5 ha). The greater the minimum distance between two parcels of the same type, the more these parcels will be considered to be 'connected to a limited extent' (remote).

Map of fragmentation of green spaces
Source: Van de Voorde et al. 2010 (based on high resolution satellite images dating from 2008).

The result shown is based on the smallest distance between an area of vegetation and its nearest neighbour (= nearest neighbour analysis). Only areas of at least 0.5 ha with an open environment or at least 0.5 or 5 ha with a closed environment were taken into account in the analysis.
Map of fragmentation of green spaces

The centre and the periphery do not only differ with regard to their respective percentages of green cover, but also concerning the spatial connectivity of their green spaces. This connectivity is less strong in more centrally located areas, where most green spaces are gardens that are enclosed by blocks of houses.
The table below shows, per type of green space (open environment of more than 0.5 ha, closed/densely vegetated environment with a surface area between 0.5 and 5 ha and closed/densely vegetated environment with a surface area of more than 5 ha), the percentage of parcels located less than 10 metres – more or less the width of a road – from a parcel of the same type.
Parcels and areas
It appears that only a small fraction (19%) of open green spaces are located less than 10 metres from another green parcel of the same type. These adjacent open spaces are mainly located in the rural area of Neerpede, on the edge of the municipality of Anderlecht.
In the case of closed green spaces many of the parcels are located less than 10 metres from another densely vegetated parcel (68% and 72%, respectively, depending on whether it concerns green spaces of more than 0.5 ha or of more than 5 ha).
In any case, the fragmentation of natural habitats is also a problem for biodiversity in the green crown of the Region, including the Sonian Forest. The fact is that the connectivity of the green spaces is not only determined by the distance between the parcels, but also by the nature of the vegetation, its ecological value or the presence of physical barriers, such as roads and fences (underestimated in the framework of this analysis).

Measures to improve connectivity between green spaces

The ruling (ordonnantie) concerning nature conservation was issued in 2012. One of the main objectives of this ruling was the introduction of a 'Brussels ecological network' (BEN). This is a coherent whole of natural, semi-natural and artificial elements of the regional territory, the conservation, management and/or restoration of which are intended to help create the conditions to ensure that the natural habitats are preserved and that there is a favourable evolution when it comes to the conservation of the species. Actually, the network comprises 'connection areas' that are necessary to stimulate the spread or migration of species. This policy of conservation or restoration of the connectivity between natural habitats has been put into practice for many years in the framework of the 'green network' programme (which also comprises social-recreational aspects) that was set up by Bruxelles Environnement-Leefmilieu Brussel in 1996 and was later included in the regional development plan.
This policy, which fits into a long-term perspective, is based on a wide range of measures: taking into account the connectivity of the natural habitats when granting planning permits, reconnecting certain waterways to the hydrographic network and bringing certain parts above ground again ('blue network' programme), developing a green walk, building eco-ducts, eco-sluices and eco-bridges (such as e.g. the recent construction of an eco-duct along which wild fauna can cross the four tracks of railway line L161 in the Sonian Forest), and managing light pollution.

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Date de mise à jour: 30/11/2015