European forest plants are migrating westwards

New research reveals nitrogen deposition, and to a lesser extent climate change, unexpectedly as the key driver behind surprising westward shifts in the distribution of plants.

These are the results of a study published in the journal Science, in which three researchers from the German Centre for Integrative Biodiversity Research (iDiv) were involved, among them Professor Dr Markus Bernhardt-Römermann from the University of Jena. The study defies the common belief that climate change is the primary cause of species moving northward. This finding reshapes our understanding of how environmental factors, and in particular nitrogen deposition, influence biodiversity.

Nitrogen emissions from air pollution identified as the key driver

While it is widely assumed that rising temperatures are pushing many species toward cooler, northern areas, this research shows that westward movements are 2.6 times more likely than northward shifts. The primary driver? High levels of nitrogen deposition from atmospheric pollution, which allows a rapid spread of nitrogen-tolerating plant species from mainly Eastern Europe. The establishment of these highly competitive species in areas with high nitrogen deposition rates often comes at the expense of the more specialised plant species.

The results highlight that future biodiversity patterns are driven by complex interactions among multiple environmental changes, and not due to the exclusive effects of climate change alone. “Climate change is often seen as the main culprit behind range shifts in plant species, but key interactions with historically important drivers are frequently overlooked”, says co-author Dr Ingmar Staude, researcher at iDiv and Leipzig University. “In recent decades, most range shifts in European forest plants are attributed to nitrogen deposition, and only to a lesser extent to climate change. This raises an important question: How can ecosystems adapt to rising temperatures while biodiversity shifts are mostly driven by other environmental changes, particularly atmospheric pollution?” Understanding these complex interactions is critical for land managers and policymakers to protect biodiversity and ecosystem functioning, according to the researchers.

Key findings:

• European forest plants shift their distributions at an average velocity of 3.6 kilometer per year.
• Nitrogen deposition rather than climate change is surprisingly the main factor behind westward distribution shifts in European forest plants.
• Several of Europe’s most emblematic forests were included in this study, such as the primeval forest Białowieża in Poland.
• The study analysed the shifts in the distribution area of 266 forest plant species across Europe over several decades, with the first measurements being taken in the year 1933 at some locations.
• 39% of the plant species shift westward. Northward shifts are only observed for 15% of the species.