The study, led by Dr Viktoria Ferenc of the Stuttgart State Museum of Natural History and the University of Hohenheim, draws on the Floristic Mapping of Baden-Württemberg, one of the oldest projects of its kind in Europe. Citizen scientists and professional botanists collected the observations between 1970 and 2023, and the dataset, maintained for over 50 years, comprises just under 2,000 vascular plant species. The research team, which also included senior author Dr Pierre Liancourt and co-authors from the museum and the University of Hohenheim, analysed this extraordinary record to ask how the state’s flora has changed and where.

The answer is more nuanced than a simple rise or fall in species numbers. Areas that were particularly diverse when the investigations began tended to lose diversity over time, and regions such as the Swabian Alb and the Black Forest have been particularly affected. According to the researchers, characteristic species and the ecological features associated with them are declining in these landscapes. At the same time, some areas in southwestern Germany have gained plant species, which means the overall picture depends strongly on where one looks and which aspect of biodiversity is being measured.

“The question of whether biodiversity is increasing or decreasing overall does not go far enough,” says Dr Viktoria Ferenc, lead author of the study and a researcher at the Stuttgart State Museum of Natural History and the University of Hohenheim. “Patterns of change vary depending on the area and the aspect of biodiversity under consideration. An increase in species numbers is not automatically positive. If widespread species expand whilst specialised species disappear, landscapes may lose some of their distinctive ecological character. Biodiversity conservation must therefore take regional characteristics into account.”

One of the study’s most important contributions is its treatment of biodiversity as more than a headcount. In addition to the number of species, the authors analysed the plants’ evolutionary relationships as well as the diversity of their traits, such as height, leaf characteristics and seed size. The various dimensions of biodiversity did not always develop in the same direction. Some areas lost distinctive ecological strategies or evolutionary diversity even though their number of species remained stable. In other words, a landscape can look unchanged on paper while its biological character erodes beneath the surface.

The direction of change also differed systematically between groups of plants. Nitrogen-tolerant and disturbance-adapted species often spread, as do highly competitive or non-native plants. In contrast, habitat specialists, species adapted to wetlands or cool conditions, orchids and species of particular conservation importance frequently decline. “It is therefore crucial to specify exactly what is to be protected,” says Dr Pierre Liancourt, a researcher at the Stuttgart State Museum of Natural History and the study’s senior author. The burnt orchid, Neotinea ustulata, formerly Orchis ustulata, offers a concrete illustration: this rare orchid of nutrient-poor, mostly calcareous grasslands has seen its habitats and populations in Baden-Württemberg decline sharply due to fertilisation and increased land use.

What drove these changes? The extent to which biodiversity changed depended, amongst other things, on the local climate, land use, atmospheric ammonia pollution, soil conditions and topography. “Using the latest statistical methods, we were able to identify patterns in this extensive data that provide important insights into how environmental factors are associated with changes in local plant diversity,” says co-author Dr Jörn Pagel from the Department of Landscape Ecology and Vegetation Science at the University of Hohenheim. “However, there was no single factor that could explain all the patterns. Rather, different aspects of biodiversity responded differently depending on local environmental conditions.”

This dependence on local context carries a direct message for conservation policy. It is not enough to simply preserve as many species as possible, the authors argue. Conservation measures should be tailored to the specific area and also take into account the ecological characteristics and evolutionary distinctiveness of the plant species found there. A region that gains a handful of widespread generalists while losing its orchids, wetland specialists and cool-adapted plants has not become richer in any meaningful sense; it has become more uniform. Protecting the distinctive ecological character of places like the Swabian Alb and the Black Forest requires knowing which species are increasing, which are decreasing, and what traits those species carry.

The study also underscores the exceptional value of long-term, coordinated citizen science and monitoring projects. “The data from the Baden-Württemberg Floristic Mapping project reveal how our region’s flora is changing and form an important basis for biodiversity research, species conservation, Red List assessments and nature conservation planning,” says Dr Mike Thiv, co-author of the study and Head of the Botany Department at the Stuttgart State Museum of Natural History. “Without the decades-long commitment of volunteer botanists, many of these changes would have remained largely invisible.” For more than 50 years, dedicated members of the public have worked alongside the museum, in collaboration with specialist societies such as the Botanical Working Group of South-West Germany, the Entomological Societies of Stuttgart and Krefeld, and the Baden-Württemberg State Agency for the Environment, to record the state’s plant diversity in standardised monitoring projects.

The mapping effort is far from finished. In 2028, the Baden-Württemberg Floristic Mapping project will begin its third survey period, and the museum is currently developing an app designed to simplify the digital recording of plant observations and enable faster access to the data. Further citizen scientists interested in supporting the mapping effort are welcome to take part. As climate change and shifts in land use continue to affect habitats and plant diversity, the continuation of this record will be essential for understanding how the flora of Baden-Württemberg, and by extension Central Europe, responds. The study, “Five decades of citizen science reveal erosion of hotspots of multifaceted plant diversity” by Viktoria Ferenc, Cornelia Krause, Jörn Pagel, Michael Boxriker, Monika Voggesberger, Arno Wörz, Mike Thiv and Pierre Liancourt, was published in Global Change Biology on 27 October 2026.

Subject of Research: Long-term changes in plant diversity across Baden-Württemberg revealed by five decades of floristic mapping

Article Title: Biodiversity hotspots in south-west Germany are losing their species richness

Article References: Biodiversity hotspots in south-west Germany are losing their species richness. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: biodiversity, plant diversity, citizen science, Baden-Württemberg, floristic mapping, Global Change Biology, hotspots, land use, climate change, nature conservation, Swabian Alb, Black Forest