The Area-representative monitoring of semi-natural grasslands (ASO) is the first national program to give a representative picture of both the extent and condition of semi-natural grasslands in Norway—a habitat with particularly high species diversity that is in rapid decline and listed as critically endangered in the 2025 Norwegian Red List for Ecosystems and Habitat Types.
Between 2021 and 2025, NIBIO mapped 713 semi-natural grasslands across the country. Based on analyses, the total area of semi-natural grasslands is estimated at 2,200–4,500 km², corresponding to 0.7–1.5 percent of Norway’s land area. This is significantly larger than previous mapping indicated. However, it should be emphasized that ASO aims to capture grasslands in all ecological conditions, not just the most intact and exclusive sites.
The results show that semi-natural grasslands are highly fragmented. About 40 percent of grasslands are considered in good ecological condition, while roughly 60 percent are no longer actively managed and are becoming encroached with bushes and trees. Changes in land use and the abandonment of traditional agricultural management are the main causes.
What are semi-natural grasslands?
“A semi-natural grassland is a species-rich grassland developed through long-term traditional agriculture, such as low-intensity mowing and grazing,” explains researcher Annette Bär, who led the monitoring work.
The land is not ploughed, artificially sown, or fertilized using modern methods, which has allowed a large diversity of plants and insects to persist.
“After 1950, artificial fertilizers became widespread, and modern, more intensive agriculture developed. The semi-natural grasslands that remain today are often pieces of land that were difficult to cultivate, for example due to steep slopes or shallow soils.”
How the monitoring was conducted
The monitoring is based on a sampling model, focusing on areas with a higher likelihood of semi-natural grasslands while ensuring that sampled plots are area-representative. This approach is necessary for sampling a habitat that is rare and covers small areas. The sampling accounts for geographic variation, including north-south gradients, coastal - inland, and elevation gradients.
“We combined aerial photo interpretation of historical and recent images with fieldwork to identify semi-natural grasslands, even those which are heavily encroached,” Bär explains.
- 100 areas of 10 × 10 km were surveyed over five years.
- Within each area, 10 plots were mapped. For every grassland in each plot, researchers recorded degree of encroachment, current land use intensity, species richness, and presence of alien species.
“This makes it possible to track changes over time and reassess ecological condition using the same variables in five years,” says Bär.
“We didn’t just want an overview of the best sites, but also those that have been encroached with bushes and trees for decades. Therefore, we mapped grasslands in all possible conditions.”
Alien and problem species pose a growing threat
Invasive native species and alien species pose a significant threat to biodiversity in semi-natural grasslands. Across ASO sites, 92 problem species were recorded, with juniper, meadowsweet, and tall buttercup being the most common. Nearly a third of grasslands contained alien species, including sycamore, Sitka spruce, and garden lupin.
“This threat is likely to increase as the climate warms and grasslands are left unmanaged,” Bär explains.
“More alien species will spread northwards and cover larger areas, ultimately threatening biodiversity. ASO data, however, provide a basis for deciding which species to control first and which areas to prioritize in nature management.”
Biodiversity influenced by many factors
Semi-natural grasslands have a unique species composition across Norway, with native species adapted to grazing and mowing regimes. They depend on high light availability and are quickly outcompeted when nutrients are added.
Analyses show clearly regional differences, with the highest species richness in Southern and Eastern Norway. The degree of utilisation (including management measures) strongly influences overall biodiversity and the presence of red-listed species. Climate change and pollution are expected to exacerbate challenges in the coming years.
ASO data are used in national biodiversity reporting and have contributed to both Norwegian Nature Index 2025 and the 2025 Norwegian Red List of Ecosystems and Habitat Types. The monitoring program also supports the classification of ecological condition in the “Open Lowlands” ecosystem and can contribute to land-use and ecosystem accounting.
“We have unique knowledge of how biodiversity is associated to different ecological condition stages,” says Bär.
“Further analyses can reveal, for example, how long grasslands can provide ecosystem services like pollination and which areas should be prioritized for restoration.”
A vital knowledge base for management
“Encroachment happens faster in some areas than others. Nutrition rich sites can become encroached within a few years, while areas with shallow or poorer soils may take 20–30 years,” Bär notes.
All ASO data are open access and integrated into established mapping tools for land management. Bär emphasizes that this knowledge is crucial for prioritizing management efforts.
“We cannot manage all semi-natural grasslands in Norway. Therefore, it is important to identify both the areas of highest current value and those with the greatest restoration potential.”