There is a common belief that species are generally moving northwards, due to climate change, with some forced out of hotter southern Europe and others suited to warm conditions now able to establish in previously cooler northern regions.
But an unexpected finding from a new study published in Science has challenged this widely held view, by showing that many forest plant species are actually moving westwards across Europe. This shift in distribution is linked to high nitrogen pollution levels in western Europe, according to the European research team, led by Ghent University and also including the UK Centre for Ecology & Hydrology (UKCEH).
Nitrogen is a key nutrient that supports plant growth. Excess amounts of the compound in the environment caused by emissions from agriculture, industry and transport support the establishment of some highly competitive species, often at the expense of more sensitive plants.
The new study reshapes our understanding of how environmental factors, including climate, forest canopy cover and especially nitrogen pollution, influence biodiversity.
The researchers analysed the shifts in the distribution area of 266 forest plant species across Europe over several decades, including from measurements taken as long ago as 1933 in some locations. Several of the continent’s iconic forests were included in this study, such as Wytham Woods near Oxford, Białowieża in Poland and Compiègne in France.
The study found there has been a rapid spread of nitrogen-tolerant forest plant species from mainly Eastern Europe, including Wood sorrel, which has been moving westward at a rate of around 5km a year, as well as tufted hair grass and tree seedlings like silver fir, hornbeam and sycamore.
While it is widely assumed that rising temperatures are pushing many species towards previously cooler areas, the new study shows that westward movements are more than twice as likely than northward shifts. Some 39% of the plant species shift westward, while northward shifts are only observed for 15% of the species.
UKCEH ecologist Dr Mike Perring, a co-author of the study, says: “Our results highlight that biodiversity is driven by complex interactions among multiple environmental factors, not climate change alone, and these dynamics will alter in the future.
“Continued monitoring is therefore required to provide essential understanding of these changing interactions, in order to guide action by land managers and policymakers to protect sensitive species and ecosystem functions.”
While it is well known that atmospheric nitrogen pollution directly harms mosses and lichens, Dr Perring says more research is needed into the impacts that changing forest plant communities will have on other organisms.
Paper information
Pieter Sanczuk et al. 2024. Unexpected westward range shifts in European forest plants link to nitrogen deposition. Science. DOI: 10.1126/science.ado0878