How much flower-rich habitat is enough for wild pollinators? Answering a key policy question with incomplete knowledge

Abstract

In 2013, an opportunity arose in England to develop an agri-environment package for wild pollinators, as part of the new Countryside Stewardship scheme launched in 2015. It can be understood as a ‘policy window’, a rare and time-limited opportunity to change policy, supported by a narrative about pollinator decline and mitigating actions palatable to policymakers. An agri-environment package is a bundle of management options that together supply sufficient resources to support a target group of species. This paper documents information that was available at the time to develop such a package for wild pollinators. Four questions needed answering: 1) Which pollinator species should be targeted? 2) Which resources limit these species in farmland? 3) Which management options provide these resources? 4) What area of each option is needed to support populations of the target species? Focussing on wild bees, we provide tentative answers that were used to inform development of the package. The final question could only be answered for floral resources. We show that the areas of some floral resource options in the basic Wild Pollinator and Farmland Wildlife Package (2% flower-rich habitat and 1 km flowering hedgerow), are sufficient to supply a set of common pollinator species with enough pollen to feed their larvae at lowest estimates, using minimum values for estimated parameters where a range was available. Initial high estimates of flower demand are way out of reach for agri-environment policies, such as a demand for 44% of the landscape to be managed as flower-rich habitat. We identify key areas of uncertainty in estimating the relevant parameters, but consider the proposed model of flower demand an important new tool for translating emerging scientific evidence into pollinator conservation policy.