Senckenberg Research Institute and Natural History Museum Frankfurt

Biodiversity mapping

"Frankfurter Kreuz" – European junction and unknown hotspot of biodiversity

Andreas Malten, Dirk Bönsel, Indra Starke-Ottich and Georg Zizka

The "Frankfurter Kreuz" intersection is the junction with the highest traffic volume in Central Europe. It was recently rebuilt from 1995 to 2000 on a large scale and is currently being affected by construction work on the S-Bahn line leading to the Gateway Gardens business park.

The inner surfaces of the cross are practically not walked on between the care measures, so that plants and animals can develop relatively undisturbed, as long as they can bear the stress caused by noise, vibrations and exhaust fumes.

As part of the project funded by the "Frankfurt/Main Airport Foundation for the Region", investigations were carried out between 2010 and 2013 on the biotope type, fauna and flora in the inner areas of the Frankfurt interchange. The adjacent areas to the north of the Frankfurt-Flughafen-Nord junction were included, so that the survey area covers a total of 31 ha.

Das Frankfurter Kreuz - Abgrenzung des Untersuchungsgebietes

319 species of higher plants were found within the study area. This corresponds to a share of more than 22% of all plant species currently present in the urban area of Frankfurt on an area of only 0.12% of the city. Nine species are classified as endangered according to the Red Lists of Germany and Hesse, another eleven are classified as in decline (pre-warning list). In addition, four species are subject to legal protection under the Federal Ordinance on the Protection of Species and the Federal Nature Conservation Act.

Dianthus carthusianorum Blasenstrauch Zygaena loti

Left: Carthusian pink (Dianthus carthusianorum); middle: The bladder shrub (Colutea arborescens), a non-native species; right: Slender Scotch burnet (Zygaena loti).

Most of the valuable species are concentrated on the remnants of dry nutrient-poor grassland rich in therophytes with transitions to heathland and bristle grassland as well as to acidic grasslands in the north of the investigated area, which, at 0.19% and 0.89%, represent only a very small part of the area. Both habitats are highly endangered in Germany and are subject to legal protection, while the meagre grasslands of acidic sites are also a habitat type under the Habitats Directive (FFH).

Maintenance measures to ensure that these areas can be kept open for the long term are therefore particularly important, especially since all these areas are endangered by scrub encroachment from adjoining fallow areas and groves. Particular attention should be paid to preventing the penetration of blackberries into the poor sandy grassland. Maintaining the grasslands is also important for the rare and in some cases highly endangered species of spider and ground beetles, which also focus on these habitats.

Sandmagerrasen Magerrasen saurer Standorte

Remains of sandy grassland in the west of the “Frankfurt-Flughafen-Nord” junction.

Acidic grassland sites in the transition to heathland in the eastern part of the “Frankfurt-Flughafen-Nord” junction.

As expected, bird species are underrepresented in the study area, as they are more susceptible to the disturbance caused by traffic noise than other groups of animals. With 16 breeding bird species, only about half as many species can be found at the "Frankfurter Kreuz" motorway intersection as would have been expected in an area of the same size without a motorway. Among the breeding birds, however, there are remarkable species such as red-backed shrike (Lanius collurio), common whitethroat (Sylvia communis) and lesser whitethroat (Sylvia curruca). The red-backed shrike in particular also benefits from the preservation of open sandy areas and poor grasslands, as it hunts its prey on the ground in such areas. On the other hand, it also needs trees and shrubs, especially thornbushes, which it also finds at the "Frankfurter Kreuz".

In addition, 16 species have been recorded as guest birds. Many of them breed in the adjoining forest areas and benefit from the mosaic of habitats in the inner surfaces of the “Frankfurter Kreuz”. Large areas of scrubland should therefore be avoided at all costs. The areas should be mowed once or twice a year, whereby it is very important to remove the dried cuttings in order to minimise further nutrient input into the large areas of ruderal meadows in the long term and to have a positive influence on the composition of the plant and subsequently also the animal species in these areas.

Centaurium erythraea Florenzusammensetzung des Frankfurter Kreuzes

European centaury (Centaurium erythraea).

Composition of the flora of the study area in percent (indigenous species, archaeophytes, neophytes).

As expected, neophytes and neozoa have been detected. The areas close to the lanes are a special habitat rich in neophytic plant species. Here, the suction effect of passing vehicles plays a role, the strongly fluctuating availability of water, the pollution, but also the deposition of dust on leaves and other plant parts. The use of road salt in winter has a special influence. This favours plant species of the coastal regions, which are adapted to salt sites. As a result, salt-tolerant species spread along inland highways. The “Frankfurter Kreuz” is no exception.

Thermophilous species of animals that have only migrated in recent decades have also been identified. However, these occur elsewhere in the Rhine-Main region, so that despite the extreme volume of traffic, no special position of the “Frankfurter Kreuz” could be ascertained with regard to the import or immigration of neozoa.


Liste der am Frankfurter Kreuz nachgewiesenen Farn- und Blütenpflanzen (Stand 2013)

Karte der Biotoptypen am Frankfurter Kreuz (Stand 2013)

Liste der am Frankfurter Kreuz nachgewiesenen Vogelarten (Stand 2013)

Liste der am Frankfurter Kreuz nachgewiesenen Tagfalter (Stand 2013)

Liste der am Frankfurter Kreuz nachgewiesenen Heuschrecken (Stand 2013)

Liste der am Frankfurter Kreuz nachgewiesenen Laufkäfer (Stand 2013)

Liste der am Frankfurter Kreuz nachgewiesenen Spinnen und Weberknechte (Stand 2013)

Abschlussbericht Frankfurter Kreuz (Stand 2017)

Lage der Vegetationsaufnahmen (Karte 2)

Vorkommen gefährdeter, geschützter und bemerkenswerter Pflanzenarten (Karte 3)


We thank the "Stiftung Flughafen Frankfurt/Main für die Region" for the funding of the project.