Motorways, connecting roads, railways and settlement and urban areas divide a landscape into individual, completely fragmented areas, and this prevents people and wildlife from moving freely in the region concerned. It threatens the natural habitats of animals and prevents their reproduction. Furthermore, recreation areas, parks, etc., lose their attractiveness and this can have negative consequences for the tourism industry.
Over the past 30 years, the fragmentation of landscapes has increased to an alarming extent. In the Central Plateau (Mittelland), the effective mesh size has been reduced by around 50% and the degree of fragmentation of the landscape has doubled. Here, the entire landscape is now fragmented. The lowest degree of fragmentation is in the mountain regions, though the fact that there are extensive undevelopable areas in these regions has to be duly taken into account. Most of the existing fragmentation has taken place in the valleys, and here the extent is greater than the calculated average figures suggest.
The "effective mesh size" measurement method was applied in order to calculate the extent of fragmentation of landscapes in Switzerland. With this method it is possible to calculate the probability of two randomly selected points in a given region being joined, i.e. not separated by barriers such as transport routes or urban development. The larger the number of barriers that fragment the landscape, the lower the probability that two random points will be connected, and thus the lower the effective mesh size.
In order to compare readings in different areas with one another, this probability has to be converted into an effective mesh size expressed in square kilometres by multiplying it by the total size of the area in question. This indicates the mesh size of a regular network with the same degree of fragmentation.
Barriers include motorways and expressways, roads in categories 1 to 4, railway lines, settlement and urban areas, mountains higher than 2,100 metres, and lakes and rivers.
In order to calculate the effective mesh size, only those landscapes in the respective areas to be measured are taken into account that can actually be fragmented. Thus, areas above 2,100 metres, as well as rivers and lakes, are excluded.