4.3 Wider Biodiversity Benefits of Wildflower Areas

Exploring the benefits of encouraging pollinators for wild plants on farmland

Lucy Capstick, Game & Wildlife Conservation Trust

As part of work carried through the extension to the BEESPOKE project, the Game & Wildlife Conservation Trust aimed to demonstrate some of the wider biodiversity benefits of wildflower areas.

The decline in pollinators on farmland is threatening populations of wild plants which depend on pollinators for reproduction. Management which encourages pollinator populations on farmland to support crop pollination could therefore also benefit these wild plants.

Aims of the study

We aimed to explore how the amount of wildflower habitat and different farming practices affected the pollination of wild plants, specifically hawthorn. We looked at hawthorn pollination because it is common on farmland in the UK and previous work (Jacobs et al., 2009) has shown that it is dependent on insect pollination for reproduction and therefore berry production (an important winter food source for farmland wildlife) but was also under-pollinated.

We compared hawthorn pollination in hedges on farms employing more regenerative practices (16) and more conventional practices (15) and with varying amounts of wildflower habitat. Regenerative agriculture practices aim to protect soil health and includes reducing tillage, increasing use of cover crops and using diverse crop rotations. These practices have some benefits for wildlife, however the impacts on pollinators are less well understood.

Survey setup

In the summer of 2022, we measured hawthorn pollination of 31 hedges across two regions of the UK, Southern and Eastern (photo 1).

We visited the hedges when the hawthorn was in flower (in May) and marked 20 clusters of flowers along a 60 m transect, counting the number of flowers in each cluster. We went back to the hedges in July and again in September to count the number of flowers in each cluster that produced immature and mature fruits respectively. The greater the proportion of flowers that produced fruits (fruit set) the higher the pollination levels.

On the May and July visits we also measured the number of pollinators present on each site; we walked along the 60 m transect and counted all the bumblebees, solitary bees, hoverflies, and butterflies seen within 2m (photo 2). After this survey we also set pan traps (small brightly coloured bowls filled with water) at either end of the transect for 48 hours. This meant we could get an insight into the pollinators present in the habitat over a longer period.

Finally, we assessed the availability of floral resources on and adjacent to the hedge at six points along the transect (every 10 m). We counted and identified the flowerheads in a 1 m x 2 m vertical quadrat on the side of the hedgerow and in a 1 m x 1 m horizontal quadrat placed on the adjacent hedge bank (photo 3).

Study results

Across the 31 sites we observed many species of pollinators on our hedge transect in May and July including 151 bumblebees, 423 butterflies and 54 solitary bees. Notable solitary bees seen included Andrena tibialis (Grey-gastered Mining Bee) which is nationally rare and Andrena haemorrhoa (Early mining bee) which is known to forage on hawthorn.

We aimed to relate the availability of floral resources to the pollinators present and consequently to the pollination of hawthorn. More nature friendly farming methods could increase the availability of floral resources and or pollinator numbers and diversity.

• We did find that fruit set of hawthorn was higher on regenerative farms in both the Southern and Eastern regions, but this did not clearly link to the number of pollinators present.

• The number of pollinators seen adjacent to the hedge varied depending on region and by the functional group of pollinators. For example, more bumblebees were seen on more regenerative farms and more butterflies were observed in the Southern region.

• Conversely in the pan trap samples more pollinators were counted on farms using more conventional practices and in the Eastern region.

We explored whether these patterns could be linked to the floral resources available. We did see a trend towards higher numbers of flower heads and umbellifers adjacent to the hedge on farms with more regenerative practices and for both regions. This could explain the higher number of bumblebees seen on these sites. Our next steps are to explore specific interactions between pollinators and plant species and to relate this to the specific farming practices used and the wildflower area in the landscape.

Acknowledgements

We thank all the landowners and managers who gave us access to their farms for this study. This work was partially funded by the BEESPOKE and partial funding also came as part of the H3 project. H3 is part of the ‘Transforming UK food systems’ research programme funded via UKRI’s Strategic Priorities Fund (BB/ V004719/1).