Sown Wildflower Strips and Hedgerows – Good for Pest Control, Pollination and Yields?

Article in Ecology Letters, (2020)

Sown wildflower strips improve pest control, and diverse, perennial strips also improve pollination services. Hedgerows in Switzerland yielded good results, while internationally effects were inconsistent.  The effects on yield were variable.

Society is calling ever more strongly for agricultural products to have as small an environmental footprint as possible. This balancing act between good yields and an intact environment is also more successful if we harness the ecosystem services that nature offers: beneficial organisms for more effective pollination and for effective pest control. It is precisely these beneficials that sown wildflower strips and hedgerows can help to encourage.

Agroscope specialists used data from 35 studies in agroecosystems in North America, Europe and New Zealand to quantitatively evaluate the effectiveness of sown wildflower strips and hedgerows for pollination and pest control. They also looked for key factors leading to the failure or success of such measures. Their aim: to develop recommendations for creating optimised sown wildflower strips and hedges. Specifically, this involved determining

• the extent to which sown wildflower strips and hedgerows improve pollination and pest control;
• the role played by the biodiversity of the flowering plants and the age of the wildflower strips;
• whether a structurally diverse, varied landscape exerts an influence; and
• whether sown wildflower strips improve harvests.

Sown wildflower strips improve pest control by 16%

The results of the literature study were clear: sown wildflower strips improve pest control on adjacent fields by an average of 16%. Whilst the Swiss hedgerows also had a positive impact on beneficials and pollination, no clear influence on pest control could be measured in the international context. The reason for this could be that with sown wildflower strips, farmers are better able to include those plant species that are particularly effective at promoting the desired beneficial organisms.  

Older, more diverse and more interconnected mean better!

In the investigated studies, the Agroscope specialists discovered that morediverse perennial sown wildflower strips are more effective at encouraging pollinating insects and their services. Flowering areas of this sort seem to offer a better food supply and better overwintering and nesting options, allowing local populations of beneficials to become established over time. The positive effects on pollination in the crops were greatest near the sown wildflower strips and hedgerows, and decreased with increasing distance. Bigger therefore does not necessarily mean better – to the contrary: the more interconnected small plantations are with one another, the greater their positive influence on pollination.

The Agroscope specialists found no consistent effects of sown wildflower strips on yields. This is presumably because the effects were highly variable, and other factors exert an even stronger influence on yield. Further research work is needed here.