How to make species-poor meadows more colorful

Biodiversity in grasslands has declined sharply in recent decades. To counteract this loss, the Swiss agricultural policy introduced biodiversity promotion areas (BPA), which promote more extensive management of agricultural land through financial contributions to farmers. In the case of meadows, this means, among other things, avoiding fertilization and delaying the first cut of the grass – this is in contrast to so-called intensive cultivation, which is primarily concerned with achieving maximum yield. Despite these measures, it is often not possible to improve the biodiversity of extensively managed meadows on the Swiss Plateau. The main reason lies in the past: decades of intensive land use have greatly reduced the seed bank available in the soil. In addition, there is often a lack of old, flower-rich natural meadows in the surrounding area from which the plants typical of these habitats could recolonize the meadows.

As part of a large-scale project co-financed by the Swiss National Science Foundation, the Federal Office for Agriculture FOAG and several Swiss cantons, researchers from the Institute of Ecology and Evolution at the University of Bern have investigated various methods for actively restoring meadows. Under the direction of Prof. Dr. Raphaël Arlettaz and Dr. Jean-Yves Humbert, they combined two types of tillage with three methods of reseeding. Their research shows that the active restoration of meadows on the Swiss Plateau can significantly increase plant diversity. With targeted restoration methods, farmers not only promote biodiversity, but also benefit from higher financial contributions. The results were recently published in the journal Agriculture, Ecosystems & Environment.

Effective methods for grassland restoration

The research group tested different methods to restore plant diversity in grasslands: The soil was either opened superficially with a rotary harrow or plowed deeper. Re-seeding was carried out either by transferring hay from a species-rich donor meadow, by sowing a seed mixture harvested from a donor meadow, or by using commercially available cultivated seeds. The various restoration methods were applied to 60 meadows in twelve regions of the Swiss Plateau in 2019. Vegetation surveys were carried out in the previous year and two and four years later, during which the plants present and their cover were systematically recorded. Based on the vegetation surveys, the researchers were then able to compare how the plant community changed over time.

29 percent more plant species in four years

The results show that after just two years, all the methods tested increased plant diversity on the restored meadows, which were previously relatively species-poor. After four years, the diversity stabilized at a higher level, with an average of 29 percent more species than before the restoration. "Thanks to these measures, 90 percent of the restored meadows reached the quality level Q2 for biodiversity promotion areas, whereas before the experiments they only had the lower quality level Q1. This higher level of botanical quality goes hand in hand with higher financial contributions for farmers," explains Laura Forgione, PhD student at the Institute of Ecology and Evolution at the University of Bern. The so-called beta diversity, which reflects the differences in species composition between regions, was also slightly higher when the hay came from a donor meadow in the same region. "This means that the local character of the restored meadows is better preserved with the hay transfer method," says Jean-Yves Humbert.

Simple and effective implementation

The study shows that plant diversity in the meadows of the Swiss Plateau can be actively improved using various easy-to-apply methods. "Even if there are small differences between the methods – for example, ploughing is slightly more effective than harrowing – all the methods tested have contributed to the majority of meadows achieving ecological quality level Q2," explains Forgione. "This allows farmers to choose the most suitable restoration method for their farm," continues Humbert. The study thus closes an important research gap. "The research was conducted over several years at the field level with a rigorous experimental design in which the different methods tested were randomly assigned to the meadows, while one acted as a control. This is the first time that such a study has been carried out at such a large scale," explains Raphaël Arlettaz. "We are now also investigating how the restoration of plant diversity in these meadows affects different groups of invertebrates," concludes Forgione.