Newly created grassland habitats that compensate for nature lost to development can effectively support wild pollinators like bees and hoverflies, according to a first of its kind study in the Netherlands. The findings are published in the British Ecological Society's Journal of Applied Ecology.
In a new study, researchers from Wageningen University compared newly created offset grasslands with existing grasslands across the Netherlands. They found the offset grasslands supported twice the number of wild bees compared to existing grasslands, and supported more species of wild bee. Hoverfly numbers were comparable across both.
The number of flower species was also comparable, but the types of flowers differed. This suggests that the offsets aren't perfect replacements for existing grasslands but can still provide important resources for wild pollinators.
The findings indicate that when implemented well, biodiversity offset sites can be as good, and may initially even be better, than existing sites in terms of wild pollinator species richness.
Klara Leander Oh of Wageningen University and lead author of the study, said: "Our study presents convincing evidence that biodiversity offsetting can be an effective tool for pollinator biodiversity conservation. However, for offsetting to work well, the created habitats need to be carefully planned and managed."
In the last century, The Netherlands has lost 90% of its semi-natural grasslands, a vital habitat for pollinators. Biodiversity offsetting schemes like the EU's No Net Loss policy and Biodiversity Net Gain in the UK are proposed as measures to halt and reverse habitat and biodiversity loss.
While the findings from this study provide evidence that biodiversity offsetting can be effective, the study only included offset sites that were successfully established. Because the level of management can vary between sites, there is still uncertainty over the effectiveness of biodiversity offsetting sites as a whole.
"A lot of uncertainty surrounds how many legally-required offsets are actually implemented and if they are properly managed.", said Klara. "Better record-keeping and long-term monitoring are needed to make sure that these offsets are actually supporting biodiversity."
In the study, which is one of the first to assess the effectiveness of biodiversity offsetting for pollinator conservation, the researchers compared 20 semi-natural grassland offsets with 20 existing grasslands across the Netherlands. The existing grasslands represented the intended end-goal of the newly created offset sites.
The researchers used transect walks, flower counts and vegetation surveys to assess floral resources, vegetation and wild bee and hoverfly abundance and diversity.
