10.12.2021 | Biodiversity

Grasslands, forests, mountains: why plant diversity is decreasing

More and more plant species are being lost, while a few are spreading over large areas. An international research team with the participation of the OeAW and BOKU has demonstrated this development for the first time in high-altitude mountains as well as in forests and grasslands. The main reason for the species shift: increased levels of nitrogen in the soil, caused by agro-industrial farming.

© Harald Pauli/ÖAW

How man-made changes in landscapes and climate accelerate the global loss of biodiversity has been examined by an international team of researchers with the participation of the Austrian Academy of Sciences (OeAW) and the University of Natural Resources and Life Sciences Vienna (BOKU) based on the shift in species composition in three very different habitats: in alpine summit zones, in the herbaceous layer of forests, and in species-rich lowland grasslands. The results of the study have now been published in the journal Ecology Letters.

Large-scale impact from human activity

The finding is worrying: plant species with large areas of distribution have increased in frequency over the past few decades, while species with small areas of distribution have declined. Although an increase in the number of species still predominates in the alpine summit zones, this is mainly due to the upward expansion of the generally more widespread species from the lower elevations.

"It is very worrying that the species change is proceeding similarly in markedly different ecosystems, indicating that we are dealing with a widespread phenomenon," co-author Harald Pauli says. He is a high-mountain ecologist at the Institute for Interdisciplinary Mountain Research of the OeAW and heads the monitoring network "Global Observation Research Initiative in Alpine Environments" (GLORIA).

High nitrogen levels in soils cause species shift

Where is this change coming from? "The main drivers of this unfavorable process are increased amounts of nutrients in the soils, for example as a result of nitrogen inputs mainly from agriculture, but also from combustion processes in transport and industry, and the warming of the soil, especially in the high mountains." Pauli explains. The plant species themselves are good indicators of high nitrogen levels: "There are many species that can reliably indicate nitrogen, such as the nettle."

The increased amounts of nitrogen have two unfavorable effects. On the one hand, they promote the growth of the widespread nitrogen-loving species. On the other hand, this leads to increased shading, which results in the displacement of the small, rarer specialists for nutrient-poor locations. "Any species that is lost is an irretrievable loss and has an impact on the ecosystem, because the diverse plant species interact with insects and other living things, such as soil organisms," the OeAW researcher says.

Intensive agriculture is the main cause of species extinction

Near-natural ecosystems have increasingly been converted into arable land and intensively managed grassland in recent decades. A large part of this area is required for the cultivation of feed for industrial animal fattening, i.e., for meat production. Pauli: "The mass animal production in turn leads to massive amounts of slurry that has to be spread on the soil – these are nitrogen compounds that end up not only on the fields themselves, but also in the landscape in Europe."

Co-author Manuela Winkler, researcher at the Institute for Botany at BOKU, is also concerned about this development: "All the study areas are located in near-natural ecosystems, i.e., far from areas already heavily degraded by intensive agriculture and settlement," she says : "Even these refuge areas of the biosphere are directly threatened by species loss and – because small-ranged plants are being replaced by large-ranged plants – by an increasing convergence of species communities."

Merging of unique datasets

The basis for the scientific data analysis was repeated surveys of the species in 141 study areas in 19 European countries. The oldest datasets go back to the 1940s. The research group, led by the German Center for Integrative Biodiversity Research, expanded these to include current data on the overall distribution of the 1,827 plant species surveyed. Researchers of the GLORIA network coordinated at the OeAW and the BOKU were pivotal in collecting the alpine data.



"Directional temporal turnover toward plant species with larger ranges across habitats", Staude, I.R., Pereira, H.M., Daskalova, G.N., Bernhardt‐Römermann,M., Diekmann, M., Pauli, H., et al., Ecology Letters, 2021
DOI: 10.1111/ele.13937