Christensen, E., Nielsen, E.M., Wind, P., Andersen, P.N., Madsen, A.B., Hansen, T.S., Høst, I., Have, P., Jensen, T., Andersen, P., Christensen E. & Kærgaard, J. 2007. NERI Technical Report No. 631, 172 p.
Summary
Transport infrastructure acts as barriers, often preventing free migration of wildlife in the landscape. When animals are crossing an arterial road e.g. a motorway, there is a risk of collision with vehicles. The establishing of fauna passages can be a means of avoiding collisions. In accordance with the landscape structures at arterial roads the passages have, so far, followed the general guidelines worked out by the Danish Road Directorate, Ministry of Transport and Energy in cooperation with the <st1:PlaceName w:st="on">Danish</st1:PlaceName> <st1:PlaceType w:st="on">Forest</st1:PlaceType> and Nature Agency under the Ministry of Environment and the National Environmental Research Institute, <st1:place w:st="on"><st1:PlaceType w:st="on">University</st1:PlaceType> of <st1:PlaceName w:st="on">Aarhus</st1:PlaceName></st1:place> in Denmark (NERI).
The establishment of fauna passages has raised several questions about their placement and effect: 1) Do the fauna passages function as planned, i.e. are they located in the landscape where the various animal species easily find them? 2) Are the surroundings of the fauna passages established in a way leading the animals to the entrances of the fauna passages? 3) Are the fauna passages designed and dimensioned for the water-living and terrestrial-living animals so that their mobility can be maintained? 4) Which animal species in the surroundings actually use or do not use the passages?
The Road Directorate has requested NERI to perform an investigation and a follow-up assessment on placement and effect of fauna passages at the motorways in <st1:place w:st="on">Northern Jutland</st1:place> .
The first types of fauna passages were pipeline constructions with a tube dimension as broad as the watercourse in order to ensure free passage of water and water-living animals. However, many terrestrial-living animal species, especially mammals, use the watercourses and other lines in the surroundings as corridors for dispersal and movement in the landscape. Thus, the fauna passages are now constructed with man-made banks, so-called banquettes, between the water body and the wall of the fauna passage. The height of the tube over the banquette varies with the distance from the wall which implies that the adaptation of some banquettes is not always optimal, especially for larger mammal species, primarily roe deer. A banquet designed with a horizontal surface that is dry all year round along the tube wall and a slope towards the watercourse fulfils the needs of various animal species.
Experience on the needs of different animal species has caused alterations in the construction of the fauna passage profile. When fauna passages are established the design is now either a rectangular or square profile. Furthermore, the banquettes are constructed with a height that the horizontal surface is not flooded by normal water level in the watercourse. The sides of the banquettes are sloping towards the water surface and often strengthened with e.g. stones in order to avoid erosion. This concept – named the wet underpass – is the basic design of fauna passages at watercourses at the motorways in <st1:place w:st="on">Northern Jutland</st1:place> .
Moreover, fauna passages have been established on terrestrial locations where it is presumed that animal species occur and distribute themselves frequently in the landscape, e.g. when roads intersect hedgerows, dikes, and fences. On such locations dry underpasses have been established and like the wet underpasses, the design is either rectangular, square or circular dependent on the surroundings.
A new type of fauna passages, namely the overpass, was introduced in <st1:country-region w:st="on"><st1:place w:st="on">Denmark</st1:place></st1:country-region> when the motor way was cut through the wooded ridge ‘Jyske Ås’ (Bilag B11). Overpasses are established where forest areas and other important corridors are transected by road constructions. The overpass is placed at the same level as the surroundings and facilitates the crossing of the road construction for most mammal species. The establishment of overpasses is possible on locations where the road surface is already lower than the surroundings or where the road surface can be lowered below ground level. It is also possible by filling to establish overpasses at locations where the road surface is in level with the surroundings.
Besides at Jyske Ås another overpass has been established at the motorway system Århus - Låsby west of Århus (Bilag B12).
NERI has selected eleven fauna passages at the motorways in Northern Jutland and the overpass west of Århus based on the following criteria in order to ensure that all the types of construction are represented (Bilag B1-12):
· Dry underpass
· Wet underpass
· Overpass
· Dimensioning
· Design
· Suitability for field studies throughout the year
· The location of the passages related to driving distances at the field studies.
The field studies were carried out throughout a year from June 1st 2005 to May 31st 2006.
Establishment of fauna passages at other motorway systems in <st1:country-region w:st="on"><st1:place w:st="on">Denmark</st1:place></st1:country-region> has given much experience on the development of design, dimensioning and adaptation of fauna passages. The experience came into use when planning the 39 fauna passages at the motorway system in <st1:place w:st="on">Northern Jutland</st1:place> . Their establishment took place from 1996 to 2001.
26 species of mammals are recorded in <st1:place w:st="on">Northern Jutland</st1:place> . Except from Sciurus vulgaris and Cervus elaphus all species were recorded in one or more of the studied fauna passages (Table 1).
The various fauna passage types are used differently by the animals and also different among the species (Figure 8). A seasonal variation is found dependent on the species and the fauna passage types. First of all the seasonal variation is related to the fact that the species’ activity and needs for migration in the landscape varies during the season is dependent on the various needs for food resources, mating, and hibernation. A strict comparison of the animals’ use of each individual fauna passage can not be accomplished, as there is no information on the density and distribution of the animal species along the motorway system in <st1:place w:st="on">Northern Jutland</st1:place> .
To attract the animals, the passages have been placed in connection with landscape corridors such as hedgerows, dikes and fences or by establishing wire fences along the road constructions that lead to the entrance of the fauna passage and prevent the animals to cross the lanes. The animals have had five to ten years to locate the fauna passages, but there seems to be no linear relationship between the level of activity and the age of the fauna passage. Apparently, the varied use of the fauna passages is caused by the various densities of the animal species in the surroundings of the fauna passages.
There is no indication that wet underpasses will be used more frequent by roe deer, even if the dimension or profile of the entrance is enlarged. When landscape bridges and overpasses are taken into consideration the activity of roe deer is markedly increased at the fauna passages. The cause might be that roe deer do not regard the landscape bridge and the overpass as obstacles. Another fact might be that this type of fauna passages is established on locations where the density of roe deer is generally higher than elsewhere.
There is a clear relationship between the size of the underpasses and the number of medium sized mammal species using them, when the activity level is related to the dimension of the entrance of the fauna passage and the tunnel index. The larger the entrance or the tunnel index the greater the number of medium sized mammal species actually is using the underpasses.
The activity level of the smaller mammals is highest on the over-passes followed by the landscape bridges. On the other hand, the dry passages are less frequently used by the smaller mammals. A reason is that the dry passages are missing an internal vegetation cover. A continuous vegetation cover yields better protection for the smaller animals against predators. An increase of the diameter may induce the vegetation cover to spread along the banks in the interior of the fauna passages thus providing the small mammals better protection.
In general, the fauna passages at the motorway system in <st1:place w:st="on">Northern Jutland</st1:place> have been placed in connection with the natural corridors of the mammal species. Most of the passages are dimensioned so that roe deer can use them, too. Except from the landscape bridges and the overpass at Jyske Ås, the main part of the fauna passages are not dimensioned for <st1:City w:st="on"><st1:place w:st="on">red deer</st1:place></st1:City> Cervus elaphus. The occurrence of <st1:City w:st="on">red deer</st1:City> is probably increasing in <st1:place w:st="on">Northern Jutland</st1:place> .
Seven species of amphibians are recorded in <st1:place w:st="on">Northern Jutland</st1:place> , but no information on specific distribution of the species is available. Thus, it is not possible to give advice on the placement of fauna passages on the motorways in <st1:place w:st="on">Northern Jutland</st1:place> for amphibians.
The barrier effect of the presence or absence of wire fence along the motorway system should be taken into consideration. ‘Jump outs’ should be established giving the animals trapped between the wired fences on either side of the lane a chance to escape. Besides, proposals for changes of specific fauna passages in <st1:place w:st="on">Northern Jutland</st1:place> are given in the report.
When constructing motorways including fauna passages it is recommended to reuse the dug tufts and rely on the present seed bank when the establishment of the vegetation cover should be accomplished. Landscape bridges and the overpasses differ from underpasses by having a continuous vegetation cover either underneath or across. The continuous vegetation cover has proven to be beneficial to many species of smaller animals as they have established a territory there presumably ignoring the passing road with its traffic.
Finally, recommendations and instructions are given to both the established motorway systems in Northern Jutland and in connection with construction of new roads in <st1:country-region w:st="on"><st1:place w:st="on">Denmark</st1:place></st1:country-region> .
Full report in pdf-format (5.513 kB)
