How plant diversity in Germany has changed over the last century

The German plant world has seen more losers than winners over the past hundred years. While the frequencies and abundances of many species have decreased, they have increased dramatically in others. This resulted in a very uneven distribution of gains and losses. This indicates a global and large-scale loss of biodiversity, as reported by a team led by Martin Luther University Halle-Wittenberg (MLU) and the German Center for Integrative Biodiversity Research (iDiv) in Nature.

It’s a strange paradox: while global biodiversity is being lost at an alarming rate, at the local level, many studies find no significant decrease in the number of animal and plant species. “However, this does not mean that the developments are not worrying,” warns Professor Helge Bruelheide, an ecologist at MLU. After all, it also depends on the species we are talking about. For example, if survival artists specially adapted to bogs or dry grasslands are replaced by common plants, the number of species often remains, in total, the same. However, diversity continues to be lost as the once very distinct vegetation of different habitats becomes increasingly similar.

To find out how strong this trend is in Germany, the MLU-led team looked at a host of local studies. Many experts provided data on more than 7,700 plots whose plant populations had been surveyed on several occasions between 1927 and 2020. These studies, some of which are unpublished, cover a wide range of habitats and provide information on nearly 1,800 species plants. This includes about half of all vascular plant species that grow in Germany. “Such time series can provide very valuable information,” says Dr Ute Jandt from MLU. Indeed, very precise botanical censuses can be carried out on plots that often only measure ten or twenty square meters. “: It is highly unlikely that plants will disappear or reappear unnoticed in such plots,” adds Jandt.

Data analysis shows a negative abundance trend for 1,011 of the species studied and a positive trend for 719. In other words, there have been 41% more losers than winners over the past hundred years. “What’s even more surprising is that the losses were distributed much more evenly,” says Bruelheide. The team discovered this by using the Gini coefficient, which is typically used to analyze the distribution of income and assets. The index shows, for example, that in many countries around the world, a small number of the rich are getting richer while a large number of the poor are getting poorer. The German plant world is experiencing a very similar trend: losses are more evenly distributed among the many losers, while gains are concentrated among fewer winners.

This last group includes, for example, the black cherry and the northern red oak, both native to North America, but which have also invaded many forests in Germany. The frost-sensitive European holly has also been gaining more and more ground during climate change. The big loser, meanwhile, is made up of many types of agricultural weeds like blueberry, grassland species like lesser scab, and wetland specialists like devilry.

According to the study, the greatest imbalance between gains and losses occurred between the late 1960s and the beginning of the 21st century. “This phase began with the strong intensification of land use. Since then, however, nature conservation measures have succeeded in weakening the still ongoing negative trend to some extent,” says Bruelheide.

Nobody knows yet if this also applies to other regions of the Earth. This is why the team advocates collecting and evaluating similar data sets from around the world. This uneven distribution of gains and losses can be seen as a harbinger of changes in biodiversity that will eventually lead to species extinction.

The new study is the result of the “sMon – Biodiversity Trends in Germany” project, which is coordinated by iDiv. As part of this initiative, data on the development of biodiversity throughout Germany is compiled and analyzed. To do this, researchers join forces with public institutions and nature conservationists.

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