April 13 (UPI) -- Plant diversity in the forests of Europe is not what it used to be. Rare plant species are being replaced by more common species at an alarming rate, according to a new study published Monday in the journal Nature Ecology and Evolution.
Across the globe, the list of threatened plant and animal species gets longer every year. But on smaller scales, some species are thriving. Researchers wanted to figure out why some plants are becoming more abundant, while others are getting snuffed out.
Scientists surveyed changes in the abundance of 1,162 different herb-layer plant species growing among 68 temperate forest sites in Europe. The survey relied on data collected and shared by a network of forest ecologists, known as forestREplot.
"This network has the advantage that the experts on the actual locations can be asked if something is unclear, and, in this way, it differs from many other large databases," lead study author Ingmar Staude, doctoral student at the German Center for Integrative Biodiversity Research and the Martin Luther University Halle-Wittenberg, said in a news release.
Analysis of the forestREplot data showed species with limited geographical ranges were more vulnerable to extinction in certain forests.
"This is not so much due to the smaller population size of such plants, but rather to their ecological niche," Staude said.
Scientists hypothesized rare and declining species were more likely to be adapted to less common soil nutrients. Further analysis showed species with limited geographical ranges were more likely to be declining in forests with excess nitrogen levels.
The numbers suggest chronic and excessive nitrogen deposition has led to a 4 percent decline in the abundance of plant species with small ranges.
In some cases, the increase in nitrogen levels has allowed rare nitrogen-loving species to thrive, but more typically, species with limited ranges are being replaced by more widespread species.
While the average biodiversity among individual forests remains relatively stable, the latest research showed plant diversity across the temperate forest biome is decreasing. The research was conducted in protected forests; biodiversity declines are likely worse in forests open to logging.
"We now have to find out whether the processes we observe in forests are similar in other biomes," said Staude.