A recently released paper by UTwente researchers has brought attention to a concerning issue in our forests: higher soil acidity than previously thought. This research not only sheds light on a worsening problem but also offers practical solutions to address the detrimental effects of atmospheric nitrogen deposition on soil.
A sour discovery
Researchers from UTwente were investigating new methods to map biodiversity from satellite and environmental DNA when they discovered extremely acidic soils in the National Parks of the Veluwe in the Netherlands.
After analysing forest soils, the researchers found that over the past 22 years, the forest areas of the Veluwe have experienced a notable drop in soil pH, from an average of approximately 4.5 to the current average of pH = 3.2. Some plots had a pH lower than 3, which is the acidity of household vinegar. The news is concerning, as these levels pose threats to forest health and biodiversity, including reduced density of foliage within the tree crown, and predisposition to tree death. Additionally, such conditions may exacerbate the risk of insect infestation and outbreak, further endangering the ecosystem's stability
Reduced density of foliage within Scots pine crowns, indicative of tree stress
The cause for the rapid acidification has been attributed to the continuing high levels of nitrogen deposition from the atmosphere, the source being mostly from intensive agriculture, and with smaller contributions from vehicles, industry, and construction.
The iconic parks of the Veluwe, including the national parks De Hoge Veluwe and Veluwezoom, and the Royal Forests of the Loo, form part of Natura 2000, the largest network of protected areas in the world, covering Europe's most valuable natural areas across all 27 European Union member states.
Recommendations in the context of the nitrogen crisis
Surprisingly, current government policies have been crafted without awareness of this extreme acidity, because field data sampling does not always cover Natura 2000 forest soils in the Netherlands. Instead, soil acidification has been estimated based on atmospheric nitrogen deposition models that lack calibration. To address this issue, this paper offers a series of recommendations to bridge the gap between policy-making and scientific understanding, emphasizing the importance of informed decision-making for the sustainable management of Natura 2000 forests in the Netherlands.
Researchers recommend urgent and biennial field sampling of soil pH in Natura 2000 forest parks, especially on the sandy push moraines as found across similar areas of northern Europe. This new sampling aims to (re-)calibrate soil pH when modelled from nitrogen deposition, ensuring accurate and up-to-date data. Additionally, ITC researchers highlight the importance of including all nitrogen sources in deposition models, advocating for the incorporation of significant sources not currently considered, such as off-leash dog walking areas in Natura 2000 forests.
More information about the project
This research was financially supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme and was conducted with the support of the Hoge Veluwe National Park, Veluwezoom National Park, and Het Loo Royal Estate in the Netherlands. The findings are the responsibility of the researchers.
