Maximising Biodiversity Net Gain benefits for pollinators

Biodiversity is increasingly becoming a watchword as we strive to balance the needs of a growing human population with the intrinsic value and ecosystem services offered by the non-human world. At the heart of the political thinking in this area is the concept of Biodiversity Net Gain (BNG), where new developments must compensate biodiversity loss above and beyond what is lost. England is one of the first countries to bring BNG into law, meaning that all eyes are on the country to see what is worth replicating — and tweaking — elsewhere.

Any moves to make habitat creation part of standard practices have potential in helping mitigate the loss of species of all kinds, but they’re especially crucial for groups that play key roles in ecosystems, and that are under threat. So, what might BNG mean for pollinators? A paper by Professor Jeff Ollerton, ecological scientist and author, suggested that BNG represents an opportunity to support different pollinator populations. However, he was also quick to point out that while habitats are the main unit of conservation in BNG, the needs of specific groups of species also need to be considered. There is, after all, little use in creating habitat if it is not suitable to support diverse life.

Pollinators need a lot more than just flowers, Ollerton noted. They require supplements from their habitat such as nesting materials, additional food and hibernation sites. Then, they also have specific needs to ensure successful reproduction. The paper also pointed to the importance of connectivity, as well as the fact that some rarer species have very particular requirements. Progress also needs to be effectively monitored, Ollerton stressed, to make sure that the landscape changes have actually made a difference to pollinator numbers and diversity.

New work led by Natalie Duffus at the University of Oxford has brought further suggestions about how BNG can pack a punch for the small creatures delivering vital ecosystem services. As it stands, the current legislation represents something of a “missed opportunity” to bring significant change for the fortunes of invertebrates, Duffus believes — and that’s largely due to how habitats are rated and so prioritised under the current policy. “For invertebrates, the low scoring habitats in the metric can have very high value depending on what features are there, where they are in the landscape and how old they are,” Duffus said. “The simplicity of the metric underpinning BNG means that there's a chance that habitats of high invertebrate value will be scored unfairly and too low, which is, I think, the biggest limitation at the moment.”

Grasslands are one type of habitat where the specific needs of pollinators and blanket ratings systems come into conflict, Duffus continued. Under the scheme, grasslands cannot have more than 5% bare ground, but they can be valuable habitat for invertebrates including ground-nesting pollinators, with even 25-50% bare ground being a valuable feature in some kinds of grassland. Likewise, more than 5% scrub is not viewed favourably in these habitats, but scattered scrub can be a valuable feature for many species.

Duffus agrees with Ollerton that the diverse life histories of pollinators are another factor which needs greater consideration. This means that they can often depend on a mosaic of habitats, with examples including hoverflies that depend on both stagnant water for juvenile development and flowers for feeding as adults, as well as species which use both flowers and rotting wood or coppice stools. Connecting the elements of the mosaic effectively brings even greater value, and indeed, features that enable movement introduced as part of BNG or any other biodiversity strategy will help animals well beyond pollinators. It is often the case with well-considered and executed landscape improvements that impact transcends target groups.

With opportunities to review and refine England’s BNG policy, all is far from lost. Changes could look to align BNG more effectively with England’s National Pollinator Strategy, for example, Duffus said, ensuring that what is effectively a compensation scheme for nature delivers to broader conservation objectives. To achieve this alignment, another crucial consideration is the need to reduce the use of pesticides and herbicides by grounds managers in new developments. Overzealous weed control, such as of dandelions, a vital pollinator resource, can hinder the success of diverse species, regardless of what habitat is being created.

Projects engineered to bring increased biodiversity come in a range of sizes. This is often dictated by whether sites are in urban or rural areas, and this is particularly pertinent in the realm of BNG, where net gain is either achieved on site, where development is taking place, or offsite at specialist locations for developing habitat at landscape scale. Although high-quality changes are possible on-site, Duffus believes off-site locations have more overall potential to deliver for wildlife in the English scheme. “There’s more space, more flexibility, and there’s also slightly stronger governance around off site BNG. The sites are on a register, they're easy to find and open to public scrutiny,” they explained. “The downside is that people like on site BNG because it keeps nature in communities. But I think BNG is not a silver bullet to do everything. I think urban green space is something that people should have anyway.”

With hundreds of countries implementing or exploring BNG, how might new adopters seek to either implement or change elements of the work so far in England? Duffus thinks that the feature most worth replicating is that the scheme starts with a biodiversity baseline, then looks to enhance it. But aside from thinking carefully about how habitats are rated, they said, to really make the most of BNG for pollinators and other invertebrates, there must be strong emphasis on governance and monitoring, with enough capacity for local planning authorities to properly scrutinise applications. Technological solutions such as 3Bee’s XNatura can play a role in the monitoring of sites navigating BNG. Designed in conjunction with leading academics, XNatura uses bioacoustics to monitor the presence of pollinators, coupled with remote sensing to capture land use change. The result is a better calculation of the impact of measures, something several major companies have already seen the benefit of.

There also need to be experts involved from the earliest possible stage in designing tailored biodiversity mitigations, avoiding one-size-fits-all solutions like simply installing ‘bee hotels’ at points around housing developments. Such simple plug-and-play measures can be useful in gardens and for public education, but if BNG represents a move to get serious about biodiversity, they cannot be the last word, and hence the informed perspectives of those with invertebrate experience should be front and centre. Helping biodiversity bounce back is no simple business — but the rewards, if done right, could be incalculable.