Nitrogen deposition poses a threat to the diversity of Europe's forest vegetation

December 16, 2013
Species found in nutrient-poor habitats, such as heather, lingonberry, crowberry and lichens in particular are sensitive to nitrogen deposition. Credit: Hannu Nousiainen, Metla.

Species found in nutrient-poor habitats, such as heather, lingonberry, crowberry and lichens in particular are sensitive to nitrogen deposition. Photo Hannu Nousiainen, Metla.

Unless nitrogen emissions are curbed, the diversity of in Europe's forests will decrease. Atmospheric nitrogen deposition has already changed the number and richness of vegetation species in European forests over the last 20–30 years. In particular, the coverage of plant species adapted to nutrient-poor conditions has reduced. However, levels of nitrogen deposition in Finnish forests remain small compared to Southern and Central Europe.

These results will be presented as part of international research published in the journal Global Change Biology. Researchers from the Finnish Environment Institute and the Finnish Forest Research Institute (Metla) participated in this research, which concludes that unless nitrogen emissions are curbed, the diversity of plant communities in Europe's forests will decrease. The work involved the examination of long-term changes in vascular plant communities within a 1 300 monitoring grid covering 28 forested areas in various parts of Europe.

The number and richness of forest floor vegetation species in European forests have changed over the last 20 to 30 years, due to wet and dry deposition of atmospheric nitrogen. In particular, low-nutrient or acidic habitats are sensitive to long-term nitrogen deposition. Among such habitats, coverage of species such as heather and may lily has been reduced in many areas, in which nitrogen deposition has exceeded a certain threshold value i.e. the critical nitrogen load.

The largest changes in vegetation have occurred in Southern and Central European forests. Although deposition has not yet markedly affected species numbers within plant communities, most new species spreading into forests during the monitoring period have been types that favour nitrogen.

Finland still has a small nitrogen load

Four monitoring areas located in Finnish nature reserves were covered by the research. These areas were subject to markedly lower nitrogen deposition (0.6–1.9 kg of nitrogen per hectare per year) compared to areas subject to greater nitrogen deposition in Central Europe (10–20 kg N/ha/year) or Italy (20–30 kg N/ha/year).

Critical nitrogen loads applied in the research are based on the previously published results of long-term field research and experiments. By critical nitrogen loads, we refer to nitrogen deposition known to have harmful effects on the functions of more sensitive organisms in the ecosystem. The critical nitrogen load in boreal forests is estimated to be fairly small (5–8 kg N/ha/y), since northern forest ecosystems are highly sensitive to the effects of excess nitrogen. Such areas in Finland include nutrient-poor and dry pine forests in particular.

Although nitrogen deposition remains small in Northern Europe, even a slight rise in long-term deposition could change the competitive relationship of vascular plants by promoting the dissemination and growth of nitrogen-favouring species.

The effects of nitrogen deposition on Finland's forest vegetation can only be investigated with the assistance of a permanent environmental monitoring network. According to long-term monitoring by the Finnish Forest Research Institute (Metla), tree felling is still the key factor in changes to floor vegetation.

This monitoring reveals a reduction in lichens throughout Finland, including in unfelled forests. In Northern Finland, reindeer grazing is the key factor in lichen reduction. Slow-growing lichens in Southern Finland can also suffer due to the rapid growth of and shading by plants benefiting from .

Explore further: Clean Air Act has led to improved water quality in the Chesapeake Bay watershed

More information: "Forest floor vegetation response to nitrogen deposition in Europe." Thomas Dirnböck, Ulf Grandin, Markus Bernhardt-Römermann, Burkhardt Beudert, Roberto Canullo, Martin Forsius, Maria-Theresia Grabner, Maria Holmberg, Sirpa Kleemola, Lars Lundin, Michael Mirtl, Markus Neumann, Enrico Pompei, Maija Salemaa, Franz Starlinger, Tomasz Staszewski and Aldona Katarzyna Uziębło. Global Change Biology (2013), DOI: 10.1111/gcb.12440

Related Stories

Greenhouse gases from forest soils

April 12, 2011

Reactive nitrogen compounds from agriculture, transport, and industry lead to increased emissions of the greenhouse gas nitrous oxide (N2O) from forests in Europe. Nitrous oxide emission from forest soils is at least twice ...

Two-pronged approach to boost forest carbon storage

October 21, 2013

More carbon will sometimes be stored in forests if a bigger variety of tree species is planted along with key species - such as nitrogen fixing trees - that are known to contribute strongly to carbon storage, according to ...

Nitrogen -- the silent species eliminator

October 12, 2007

Nitrogen pollution from agriculture and fossil fuels is known to be seriously damaging grasslands in the UK. A new European study is starting to show that the effect is Europe-wide, confirming that current policies to protect ...

Recommended for you

New Amazon threat? Deforestation from mining

October 18, 2017

Sprawling mining operations in Brazil are destroying much more of the iconic Amazon forest than previously thought, says the first comprehensive study of mining deforestation in the world's largest tropical rainforest.

Scientists determine source of world's largest mud eruption

October 17, 2017

On May 29, 2006, mud started erupting from several sites on the Indonesian island of Java. Boiling mud, water, rocks and gas poured from newly-created vents in the ground, burying entire towns and compelling many Indonesians ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.