Research

Biotope mapping of the urban area of Frankfurt

Since the founding of the working group in 1985, the mapping of biotope types in the urban area of Frankfurt has been a central component of its remit. The first mapping round took place between 1985 and 1990, and since then regular revision mapping has been carried out to continuously update the database. The seventh mapping round began in 2024 and is currently underway. The biotope mapping in Frankfurt has thus developed into an important long-term monitoring programme.

A mapping round usually lasts six years, with different areas of the city being mapped according to a specific rhythm (figure map). The city centre (coloured in blue) and the municipal forest (coloured in green) are only surveyed in every second round.

From the outset, the central working tool has been the biotope mapping key, in which the various mapping units, consisting of natural habitats and urban structure types (e.g. various forms of settlements or traffic areas), are precisely defined. The working group developed its own mapping key, which is adapted to the conditions in Frankfurt and has been modified and improved several times over the decades. The fourth version of the biotope mapping key (Bönsel et al. 2007) is currently in use, and a fifth revised and supplemented version is currently being prepared. The citywide mapping of the urban area is carried out at a scale of 1:2000, with a focus on the documentation of legally protected biotopes and habitat types listed in Annex I of the Habitats Directive of the European Union.

The results of the mapping are digitised and are available as geodata. These are freely available on the geoportal of the City of Frankfurt (in the menu: Themen -> Fachdaten -> Umwelt -> Biotopkartierung).

The extensive and long-term data basis enables a quantitative and spatial analysis of the changes in the various biotope types within the urban area. This also allows to draw conclusions about the causes of change, such as land use intensification or the effects of climate change. In this way, the working group can also develop protective measures and recommendations for action to counteract negative developments.

Flora of Frankfurt

Since its foundation, the Senckenberg – Leibniz Institution for Biodiversity and Earth System Research has focussed its research on the flora of the Rhine-Main region and Hesse. This is documented by numerous publications as well as extensive herbarium collections and unpublished data in the Herbarium Senckenbergianum (FR). The biotope mapping in Frankfurt and special projects on biodiversity recording provide a unique, comprehensive database on the inventory and distribution of plant species in Frankfurt.

Based on this data and years of field work, a list of ferns and flowering plants in Frankfurt am Main has been compiled, which can be downloaded here. The list was published in September 2008 in the journal Senckenbergiana biologica. The species list is updated at regular intervals.

• List of ferns and flowering plants of Frankfurt am Main, as at April 2009, with explanatory notes [in German]
• Updated species list of ferns and flowering plants of Frankfurt am Main, as of September 2019 with explanations above [in German]

Please cite the list of Frankfurt’s Flora in publications as follows: Bönsel, D., Ottich, I., Malten, A., Zizka, G. (2008). An updated list of the vascular plants of Frankfurt am Main (Pteridophyta & Spermatophyta). Senckenberg. Biol. 88 (1): 111-121.

The website www.flora-frankfurt.de has been online since 2009 and makes the results of botanical research in the city accessible to a wide audience. All species recorded from Frankfurt are presented here in short portraits. The known occurrences of the species are shown on maps with a variety of visualisation options. A special feature of the website is that it also provides information on the history of the species in the region, e.g. their spread, previous utilisation, decline and causes of threat.

The website is currently being fundamentally revised and is expected to be available with a new design and extended display options from summer 2025.

Monitoring of species and habitats of conservation concern

An important research component of the working group for biodiversity mapping is the monitoring of selected species and habitats in the urban area that are of great importance from a nature conservation perspective. The monitoring was launched in 2023 and comprises a total of 24 study areas which represent key habitat types in Frankfurt. These include agricultural areas, new (recently created) and old (long-established) municipal parks, renaturalised areas, orchards, urban forest remnants, forest ponds and other water bodies (three study areas for each of the eight habitat types). The following surveys are carried out on all 24 areas every three years:

• territory mapping of all breeding birds
• recording of all ferns and seed plants by compiling complete flora lists
• monitoring of the Great Capricorn Beetle (in study areas where the species recently occurs)

A particular focus of the monitoring is on the so-called target and responsible species of Frankfurt’s species and biotope protection concept (ABSK). Target species as defined by the ABSK are species in need of protection that are considered particularly rare or endangered or whose special habitat requirements are categorised as relevant for other species groups. Species of concern are species for which the City of Frankfurt and the State of Hesse bear a high degree of responsibility for their conservation and species that are either highly endangered or whose survival depends on stable populations in urban areas.

The 24 study areas are supplemented by 16 additional study areas in which individual species groups are recorded for which these areas are of particular importance.

In addition to monitoring the habitats that are relevant to nature conservation, the breeding populations of selected bird species throughout the city are also recorded every three years. These include the Little Ringed Plover, Great Reed Warbler, Grasshopper Warbler, Turtle Dove, White Stork, Marsh Harrier and Red-backed Shrike (all of them are target or responsible species of the ABSK).

The monitoring of species and habitats of conservation concern is intended to enable a long-term analysis of the change in species communities and the changes in populations of endangered species in Frankfurt. The aim is to identify the influences of land use, climate change and other factors. In some cases, results from earlier studies by the working group can also be incorporated.

Monitoring of neobiota

Neobiota are species that have arrived in an area (in this case the urban area of Frankfurt) after 1492 under the direct or indirect influence of humans and reproduce independently there. This does not include species that are exclusively cultivated or kept. Neobiota occur in different systematic groups. In the case of ferns and seed plants alone, several hundred neophytic species are known from Frankfurt’s urban area. Neobiota also exist in various animal groups (e. g. mammals, reptiles, insects) and in fungi.

Following on from the monitoring of species and habitats of conservation concern (see above), the working group for biodiversity mapping also carries out a targeted survey of newly immigrated plants (neophytes) and animals (neozoa) in the 24 study areas and 16 additional study areas. This involves locating newly immigrated plant and bird species with pinpoint accuracy and determining their population size. In addition, the occurrence of the spreading neozoa Rose-ringed Parakeet (Psittacula krameria) and Bar-headed Goose (Anser indicus) are recorded throughout the entire urban area.

By repeating the surveys every three years, dispersal patterns and population trends of non-native species can be determined. From this, assessments of threats to the native flora and fauna can be developed and, if necessary, the success of mitigation measures for invasive species can be assessed.

Monitoring of permanent observation plots

Permanent observation plots are primarily used to survey flora and vegetation, which are repeatedly recorded on exactly the same areas over long periods of time. In addition to a complete flora list, this also includes an estimate of the proportion of cover of the individual plant species in the various vegetation layers. From this, medium and long-term changes can be recognised and their influencing factors can be identified.

In 2023, the working group for biodiversity mapping started a monitoring of over 100 permanent observation plots in the Frankfurt city area, covering a wide range of plant communities and habitats. It includes forests, grassland, water bodies, gravel areas, nutrient-poor grassland and heathland. We use newly established permanent observation plots as well as existing plots for the monitoring programme which allow comparisons to be made with previous vegetation surveys. The surveys are generally carried out every three years.

Development of protection concepts

Drawing up conservation and protection concepts has been part of the working group’s remit for decades. Four comprehensive conservation concepts for amphibians, reptiles, the Great Capricorn Beetle (Cerambyx cerdo) and grassland biotopes are to be developed as part of the 12-year research cooperation with the Environmental Agency of the City of Frankfurt. One focus here is on creating an up-to-date picture of the situation, identifying the main causes of endangerment and developing practice-orientated proposals for solutions, also with regard to the expected effects of climate change and changes in land use.