Biodiversity: When more plant species are not a good sign

At first glance, it sounds like good news: in many European habitats, there are now locally more plant species than in the past. An international study led by Martin Luther University Halle-Wittenberg analyzed 57,390 vegetation time series from across Europe. In total, 199,282 individual vegetation surveys were included; some time series go back more than 100 years.

The central result: on average, European plant communities gained about 0.7% vegetation cover and 0.2% species richness per year. At first, this sounds positive, but it is not necessarily good news. The study also shows that the winners often include generalists, non-native species and plants with broad ecological niches.

More plant species do not automatically mean more nature

What matters is not only how many plant species grow on a site, but which ones. A meadow, a bog or an alpine site can become locally richer in species and still lose its original character.

This happens, for example, when rare, specialized species are joined or, over the long term, displaced by common and adaptable plants. Such generalists can cope with many conditions: more nutrients, disturbed soils, changed land use, drought or rising temperatures. In the statistics, the species count then rises, while ecologically the habitat can lose quality.

That is why it is important to distinguish between:

• Local species richness: How many plant species occur at a specific site?
• Habitat quality: Do the typical, specialized and rare species of this habitat still occur there?

The researchers also found no general increase in overall European species diversity within habitat types, known as gamma diversity. This suggests that new species are not simply being added everywhere. Rather, plant communities are changing: some species arrive or increase, while others disappear.

Strong changes in bogs and wetlands

The most conspicuous changes appeared in bogs and wetlands. Especially there, an increase in species can be a warning signal. Bogs are extreme habitats: wet, nutrient-poor, low in oxygen and often shaped by highly specialized plants (and animals).

When such sites are drained, disturbed or become richer in nutrients, additional species can move in. This increases local species richness, but often shows that the bog is losing its typical conditions. In degraded bogs, for example, peat mosses, sundew species, cottongrasses or bog-typical sedges can decline, while purple moor-grass, birches, willows or other more competitive species increase. The plant list does not necessarily become shorter, but it becomes less characteristic of a bog.

The Alps also show this change

A similar pattern can be observed in mountains. As the climate warms, warmth-loving species move to higher elevations. This can initially increase the number of species at alpine sites. But for cold-adapted high-mountain plants, the available habitat becomes smaller.

Typical alpine specialists such as glacier buttercup, alpine rock-jasmine, various saxifrage species or alpine cushion plants are adapted to short growing seasons, cold, snow and open sites. When species from lower elevations move upward, these specialists face stronger competitive pressure. Eventually, the room to retreat ends at the summit.

Here, too, more species at a site can indicate a transitional phase, but not necessarily an ecological improvement.

Grassland: weaker trends, but great importance

In grassland, the average changes were smaller than in bogs and wetlands. Even so, grassland is a good example of why species counts alone are not enough.

A species-rich nutrient-poor meadow with orchids, arnica, meadow clary, yellow rattle, oxeye daisies or common knapweed is ecologically different from a nutrient-rich, densely vegetated site with dominant grasses, docks, stinging nettles or emerging woody plants.

Many species-rich meadows depend on extensive management: if they are fertilized too heavily, mown too often or no longer managed at all, competitive relationships shift in favor of a few robust species.

Even if additional species temporarily appear on a disturbed or abandoned site, light-loving specialists can disappear over the long term. The site may then seem greener and denser, but ecologically it is not more valuable.

Arable wild herbs: loss despite a “green” landscape

Arable fields also show how strongly plant communities can change. Many typical arable wild herbs have become rare today or have partly disappeared completely from Germany, even though agricultural landscapes still appear “green.” Species such as corncockle, field larkspur, lamb’s lettuce, cornflower or common poppy were once typical companions of extensively managed arable fields.

Herbicides, seed cleaning, heavy fertilization and dense crop stands have driven back many of these species. They are often replaced by a few robust species that can cope with nutrient-rich and intensively used sites. Here, too, the issue is not only the amount of plant growth, but the composition of the vegetation.

Landscapes are becoming more similar

The study’s most important message is not that Europe’s plant world is becoming more diverse, but that many plant communities are changing. Robust, widespread species often benefit. Specialized species lose their particular habitats.

This leads to gradual homogenization. Bogs become drier and overgrown with shrubs. Nutrient-poor meadows become denser and richer in nutrients. Alpine habitats face competition from lower elevations. In this way, very different habitats can increasingly turn into a more similar kind of “ordinary green.”

A local increase in species can mask ecological losses. If you only count how many species occur at a site, it is easy to overlook that rare or habitat-typical species are disappearing.

This is not about preventing natural change. Change becomes dangerous where specialized species disappear, habitats lose their typical characteristics and the same robust species increasingly benefit.

Not every change is harmless

Plant communities change naturally. But today, climate change, intensive agriculture, nutrient inputs, drainage and the global spread of species by humans act at the same time. The problem, therefore, is not every new species, but above all the loss of typical habitats and specialized plants.

In conservation, “native” also does not simply mean “German” or “not German.” What matters is whether a species occurs naturally in an area or has arrived there through human influence—and whether it displaces other species or habitats there.

Species count is not what matters most

Biodiversity cannot be assessed by species counts alone. What matters is which species increase, which disappear and whether a habitat retains its typical characteristics.

The current study found that vegetation cover and species richness in Europe are indeed increasing each year, but this increase is often accompanied by generalists, non-native species and a changed species composition.

For species conservation, this means we need to look more closely. A site can become locally richer in species and still lose ecological quality. Especially with plants, this change often happens slowly and inconspicuously—it often becomes visible only when old vegetation surveys are compared with today’s data.

---

Source

• Kambach, S., Jandt, U., Acosta, A. T. R., et al. (2026): Habitat-specific trends in taxonomic, functional, and phylogenetic diversity in European plant communities over a century. Nature Communications 17, 4208. https://doi.org/10.1038/s41467-026-72112-5