What role play flower-rich field margins in agriculture? And do these flower strips enhance biodiversity? These were some of the central questions of a two-year collaborative research programme that involved farmers, agronomists, conservationists and IBED researcher Paul van Rijn. The research will be continued thanks to a two year European subsidy to study and implement Functional AgroBiodiversity in Northwest Europe.
Flower strips at the edge of arable fields can have various functions. They may create a buffer between crop and ditch, thereby limiting the run-off of nutrients and pesticides into the water. Depending on the plants that they harbour, the strips can also support insect biodiversity, including pollinators and natural enemies of pests and the ecosystem services they provide to the farmers. In a two-year long monitoring programme (2017-2018) a team of organisations studied the importance is of flower-rich field margin strips for these different functions, funded by the Ministry of Infrastructure and the Environment.
The Hoeksche Waard, an agricultural area south of Rotterdam, is unique for its high number of field margin strips. Paul van Rijn, researcher at the UvA Institute for Biodiversity and Ecosystem Dynamics (IBED), has been studying these landscape elements for more than 10 years, with emphasis on their function for natural enemies of pests. With his research he showed that only specific flowers are suitable to feed the important insects, such as hoverflies, in their non-predatory life stages. The flower strips in the Hoeksche Waard have been designed to show high numbers of these suitable flowers during the critical season. The effectivity of these tailor-made flower strips for the natural pest control in the crops had not been studied yet.
In both 2017 and 2018 more than 30 agricultural fields with field margin strips were selected on their type and vegetation composition. Throughout the season, the insect fauna in the margin strips, as well as in the agricultural fields, were monitored by respectively volunteers of the conservation society ‘Hoekschewaards Landschap’ and researchers from Wageningen University and Research.
The results of the study show clear functional differences between different types of field margins. While annual flower strips are generally very flower rich, in perennial strips the amount of flowering forbs decreases with age due to the growing dominance of grasses. Within this range of field margin strips, insect diversity clearly increases with the amount of forbs. Also the number of wild bees (especially bumblebees), hoverflies and other natural enemies, such as lacewings and ladybeetles, increases with the amount of forbs in the field margins, whereas the number of butterflies and dragonflies are not affected by it.
In potato fields there was a considerable number of aphids, but the numbers generally decreased from late June onwards. This decline went faster in fields with more natural enemies (mainly lacewings and hoverflies). Van Rijn explains: 'This indicates the importance of natural enemies for the regulation of these pests. Moreover, the rate of aphid population decline was higher in fields with field margins that contained more flowering forbs.'
The farmers, immediately informed on the results of the monitoring in their fields, largely refrained from using insecticides, in contrast to common practice. 'The results indicate that flowering field margins in combination with pest monitoring can contribute to agrobiodiversity in two ways: by providing habitat and resources (nectar and pollen) for a range of insect species and by reducing the use of insecticides,' says van Rijn.
The important results of this two-year study can continue to be validated, thanks to a European Interreg NWE subsidy for the project 'FABulous Farmers', in which IBED is involved. This project aims at studying and implementing Functional AgroBiodiversity (FAB) in Northwest Europe. Within this project Paul van Rijn will continue the coordination of the broad monitoring scheme in the Hoeksche Waard, including effects on aquatic fauna and a wide range of ecosystem services. This programme will result in recommendations for European and national authorities on the use of FAB in farming, to support sustainable and nature-inclusive agriculture.