Nitrogen Pushes European Forests Westward Over Decades

Researchers have documented a shift in plant species ranges toward the poles or higher latitudes in the face of climate warming, but Pieter Sanczuk and colleagues now reveal another unexpected pattern of range shift. For decades, understory plants in European temperate forests have been on the move westward, spurred by differences in nitrogen deposition rates. Westward species distribution shifts were 2.6 times more likely than northward ones, according to the researchers, who also noted that forest canopy changes played a role in this shift as well. The findings suggest that factors beyond climate change, such as atmospheric pollution, are also an important part of redistributing biodiversity. Sanczuk et al. reviewed plant community data collected for 266 understory plant species from surveys between 1933 and 1994 and paired those data with resurvey information collected between 1987 and 2017. They found a trend of species ranges moving west over multiple decades that was connected to atmospheric nitrogen deposition rates. As generalist species shifted to take advantage of high-nitrogen areas, species that had experienced lower nitrogen depositions rates across their distributions initially had faster westward shifts. Colonization along the east-west axis was more closely related to nitrogen and sulfur deposition rates than measures of climate change such as temperature and precipitation.