A new study by researchers from the University of Gothenburg surprisingly shows that nitrogen pollution is the main driver of forest plant expansion in Europe. Climate change does not affect plant movement to the same extent.
High levels of nitrogen pollution cause many forest plant species, such as various grasses, shrubs and herbs, to move westwards in Europe's continental forests. Nitrogen deposition can also disadvantage other species and lead to changes in biodiversity.
"The results of our study go against the common belief that climate change is the main reason for species to move to new locations, especially northwards. It gives us a better understanding of how different environmental factors, and in particular nitrogen pollution, affect the distribution of plants," says Anne Bjorkman, senior lecturer in plant ecology at the University of Gothenburg and co-author of the study.
Many factors
It is widely believed that rising temperatures are driving many species towards cooler, northern areas. But the study shows that the westward movement of plants in Europe's continental forests is 2.6 times more likely than northward movements. The primary driver for this is high levels of nitrogen deposition from air pollution, allowing for the rapid spread of nitrogen-tolerant plant species from mainly Eastern Europe.
"There are many factors that determine whether a plant species can establish and be successful in a new location. These include the density of foliage in the forest, soil, climate and water availability. Future biodiversity patterns are driven by complex interactions between multiple environmental changes, not just climate change. Understanding these interactions is crucial for land managers and policy makers to protect biodiversity and ecosystem functioning," says Anne Bjorkman.
Counting plants
The establishment of these highly competitive species in areas of high nitrogen deposition can sometimes be at the expense of the more specialised plant species. The average speed at which plants spread is just over 3.5 kilometres per year.
"At a time when we are rapidly developing new modern methods for environmental monitoring, such as remote sensing, eDNA and AI, it is important to remember that traditional methods, such as walking in the forest and counting plants, can still provide valuable insights into biodiversity," says Caroline Greiser, a landscape ecologist at Stockholm University and the Swedish University of Agricultural Sciences, and co-author of the study.
Scientific article in Science: Unexpected westward range shifts in European forest plants link to nitrogen deposition
