10 percent natural habitat is insufficient for pollinator recovery

Insects contribute to ecosystem services because of the pollination of all kinds of crops, but populations have been declining for years. New research shows that better management of the remaining natural landscape elements in the agricultural landscape, such as hedges and flowery verges, is insufficiently effective to halt pollinator loss. To combat the decline of pollinators, more natural habitat must be created in the Netherlands. To this end, the EU biodiversity strategy aims to fill 10 percent of agricultural landscapes with natural landscape elements by 2030. The current study, based on 59 studies worldwide, shows that this percentage is not enough: bees, bumblebees and butterflies need between 16 and 37 percent of the habitat in a landscape for effective protection.

Area and quality must increase

The study examined how the area and quality of natural habitats influence the populations of wild bees, bumblebees, hoverflies, and butterflies. For all species groups, this simple relationship rang true: the more natural habitat, the more pollinators in farmland areas. Habitats with more flowering plants also harboured more pollinators of all groups than areas with few flowers. “However,” first author Gabriella Bishop says, “it is better to focus on increasing the area of natural habitats first, instead of on managing small habitats, even when they have many flowers.”

Differences between groups of pollinators

Four groups of pollinators were included in the study. For solitary bees and bumblebees, the proportion of habitat required at landscape scale was comparable at 16 and 18 percent. For butterflies this figure was much higher at 37 percent. It was similar to the 38 percent found for tropical bees, but that outcome was based on only two countries and should therefore only be considered as a first indication. Only for hoverflies did the required habitat cover come out lower at 6 percent, within the 10 percent limit of the European target. These differences can largely be explained by the local densities of the species groups and the extent to which they depend on (semi-)natural habitats in the landscape. Hoverflies are not only flower visitors, and very mobile at that, but as larvae also act as pest control agents that can thrive in agricultural areas. They therefore often occur at higher densities, whereas in butterflies the densities are much lower and the dependence on semi-natural vegetation is greater. For butterflies, achieving a robust nature network is therefore crucial. The halving of the European grassland butterfly population over the past thirty years underlines this.

Only butterflies were analysed from the larger group of Lepidopterans. Moths are still an underexposed group of pollinators, but appear to be more important than previously thought. Unfortunately, there were still insufficient data on this species group to include them in the study. Fortunately, in the context of the Nature Restoration Regulation, extensive efforts are being deployed to obtain a reliable picture of the population development of all groups of pollinators!

Quality and long-term

Not only the quantity, but also the quality of the habitat is important, the study emphasises. Pollinator conservation in Europe focuses heavily on temporary measures on small areas of productive land, such as wildflower strips along crops. Previous research has shown that this does lead to a temporary increase in insects and pollinators. However, the new study shows that much more habitat is needed and that the quality of the new habitats must be guaranteed in the long term. Last author Thijs Fijen: "To genuinely make a difference, it should be possible to reward farmers for the long-term creation and maintenance of new natural habitats on their farms. This means 20 to 30 years, otherwise it results in too much insecurity for farmers and benefits for pollinators will be too low." 

Biodiversity stands for more

There is increasing evidence that biodiversity, such as diversity in species and ecosystems, is not only good for nature, but for people as well. This not only concerns clean water and clean air, but also the food supply, which strongly relies on pollination by all kinds of insects. In the EU, it has therefore been agreed in the Nature Restoration Regulation to reverse the decline of biodiversity, the decline of pollinators in particular, and to head towards restoration. The EU has set itself the goal of creating or maintaining a certain percentage of natural landscape elements in the agricultural area. Member States are currently working out plans on how they can achieve this. At the moment, the grassland butterfly indicator already offers a tool for monitoring. In the coming years, this will be expanded further and the monitoring for moths, bees and hoverflies will be deployed at a European level. Hopefully, these efforts for landscape restoration will soon demonstrate the turnaround from decline to recovery!

Meer informatie

• Article: Critical habitat thresholds for effective pollinator conservation in agricultural landscapes.
• The research was carried out in the framework of the EU project SHOWCASE, which identified synergies between agriculture, ecosystem services and biodiversity restoration.

Text: Gabriella Bishop, Thijs Fijen, David Kleijn, Wageningen University & Research; Michiel Wallis de Vries, Dutch Butterfly Conservation
Images: Kars Veling (lead photo: hoverfly, Eristalis nemorum), David Kleijn, Dutch Butterfly Conservation