In this research work soil construction and vegetation of existing wildlife overpasses were investigated. This was to get knowledge about which characteristics a substrate should have in order to establish certain plant communities, with focus on water/air balance.
Examination of 12 several years old wildlife bridges was conducted from August 2012 until July 2014. The overpasses are located in different natural areas within the federal states of Baden-Wuerttemberg, Mecklenburg-West Pomerania, Lower Saxony, North-Rhine Westphalia and Thueringen.
All locations showed an extensive anthropogenic modification of soil and stratification. Nevertheless essential conditions for the growth of woody plants are adequately met. Without connection to the natural soil, a thin layered composition of more than 80 cm of thickness was determined to always allow the establishment of a permanent bosk coverage. For the prevention of wooden plants, other substrates are necessary.
Continuative investigations developed compositions of substrates determined for wildlife bridges without contact to natural soil. For this purpose, 15 vegetation substrates were developed and studied for their suitability. Results confirm that the majority of material components with open-pored grain structures made from recycled stone or natural stone are suitable.
Practical tests with a material mixture were conducted as part of a bat bridge building project.
With specific reference to the type of vegetation and its functional goal, finally five standard construction measures were formulated. These are for the vegetation types of heath and neglected grassland, open meadows, open meadows with bushes, bushes and bosks and, as a speciality, bridges for bats.
Finally a specification profile for substrate use on wildlife overpasses soil is presented. This is strictly oriented on the physical soil characteristics.
wildlife overpass; greenbridge; substrat; soil