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Wildlife viaducts are first and foremost aimed at the conservation of biological diversity, although in exceptional cases they may perhaps be about individual and selected species.
Normally, though, green bridges are there to create the environmental living conditions to encourage and facilitate the mobility of species sensitive to barriers. They should not merely be there for just one, but many species in need of conservation. Barrier-sensitive species range from flightless small animals such as many beetles, grasshoppers and snakes to large, inherently shy animals such as deer.
But who is thinking about plants?
Yet many plants are dispersed with the help of large animals and establish colonies where those animals create new sites suitable for plant germination. Typically these plants are dependant on large animals moving through the landscape undisturbed and frequently. Hence plant diversity needs some disturbance to create the conditions where more delicate plant species can survive in the face of colonization by stronger, more aggressive species. These weaker plant species find developmental niches in the »slipstream« of herbivores. To accomplish this, deer and other species must to be able to live undisturbed, meaning they can forage and rout around either side of, and on, the green bridge. The bridge is an ideal place to observe this type of behaviour. Peace is of the utmost importance if large animals are to use a green bridge intensively. Otherwise the expensive building costs are simply a waste.
Other than peace, proximity to migratory spots and adequate ground cover for seclusion are crucial for large animals. For deer, a green thoroughfare must not be too narrow since they are wary of confined spaces. It is ideal if water bodies and other natural attractions are also present – as is the case at Kiebitzholm. Its success as a green bridge is down to a combination of effective fencing, good isolation from disturbance, strict hunting prohibition and routes that encourage human visitors to give it a wide berth.