Nature: How German plant diversity has changed over the past century

Over the past hundred years, Germany's plant world has had more losers than winners
.
While many species have decreased in frequency and abundance, they have increased
significantly in others.
This creates a very uneven
distribution of profit and loss.
A team led by Halle-Wittenberg (MLU) of Martin Luther University and the German Center for Integrative Biodiversity Research (iDiv), reports in Nature that this shows that biodiversity is being lost
across the board and on a large scale.

It's a strange paradox: while global biodiversity is disappearing at an alarming rate, at the local level, many studies have not found significant reductions
in the number of animal and plant species.
"However, this does not mean that the development of events is not worrisome," warned
Professor Helge Bruelheide, an ecologist at MLU.
After all, it also depends on which species
we are talking about.
For example, if a survival artist who specializes in peatlands or dry grasslands is replaced by common plants, the total number of species usually remains the same
.
However, diversity is still being lost because what was once very different vegetation and different habitats are now becoming more and more similar
.

To find out how strong this trend is in Germany, the MLU-led team looked at a large number of local studies
.
Many experts have provided data from more than 7,700 plots that surveyed plant populations
several times between 1927 and 2020.
The studies covered a wide range of habitats and provided information on nearly 1,800 plant species, some of which had never been published before
.
This includes about half of the vascular plant species
that grow in Germany.
Dr.
Ute Jandt of MLU explains: "Time series like this can provide very valuable information
.
" This is because very precise plant censuses can be carried out
on land that is usually only 10 or 20 square meters.
Jandt adds: "In this case, it is highly unlikely that
the plant will disappear or reappear without being noticed.
"

Analysis of the data showed that of the species studied, 1011 had a negative abundance trend and 719 had a positive abundance trend
.
In other words, over the past hundred years, there have been 41%
more losers than winners.
"What's even more surprising is that the distribution of losses is more even," Bruelheide said
.
The team discovered this using the Gini coefficient, which is often used to analyze the distribution
of income and property.
For example, the index shows that in many countries around the world, a small number of rich people are getting richer, while a large number of poor people are getting poorer
.
The German plant community also sees a very similar trend: losses are more evenly distributed among the many losers, while gains are concentrated in a small number of
winners.

The latter category includes black cherries and northern red oaks, both of which originated in North America but now also occupy much of Germany's forests
.
In the process of climate change, frost-sensitive European wintergreen has also gained more and more land
.
On the other hand, the big camp of losers includes many types of agricultural weeds such as cornflowers, meadow weeds such as small scabies, and wetland weeds such as devil grass
.

According to the study, the worst imbalances occurred between
the late 60s and early 21st centuries of the 20th century.
"This phase begins with an intense intensification of
land use.
Since then, however, some successful nature conservation measures have somewhat dampened the ongoing negative trend," Bruelheide said
.

No one knows if this also applies to the rest
of the planet.
That's why the team advocates for collecting and evaluating similar datasets
from around the world.
This uneven distribution of gains and losses can be seen as an early warning sign of changes in biodiversity that will eventually lead to species extinction
.

The new research is the result of the "sMon - Biodiversity Trends in Germany" project, which is coordinated
by idv.
As part of this initiative, data on
biodiversity development across Germany are being compiled and analysed.
To this end, researchers are working
with public institutions and conservationists.