Wild bees a buzz in Vienna – new research on bees and green roofs

Rooftop garden in Vienna studied in the research (Image: Living Roofs)

Green roofs heed to offer high flower abundance from spring through to autumn. Whilst sedum species are the ‘work horse’ of green roofs, they do have a limited flowering period. There is a need, therefore, to increase the wildflower diversity on green roofs. This is one of the key findings of new research in Vienna on wild bees.

Wild bees – wildflowers are important on green roofs

Whilst sedums flower in May and June in Vienna, many bees are active from early spring through to late autumn. This limits the resource available for bees.  Increasing the the diversity of wildflowers will ensure green roofs provide benefits throughout the season. This is particularly important for oligolectic bees. These species have a preference for specific flowers, typically of a single genera. The study also found that green roofs with wildflowers were particularly important in spring (March and April) and late summer (July and August). This was true for generalists bees as well as the specialist species.

Nesting habitat for wild bees on green roofs

The research also concludes that providing areas of deeper substrate would help support ground-nesting bees. This agrees with research undertaken in Switzerland and the UK. Above-ground nesting specie of bees appear to be able to find adequate places to nest in the wider urban environment. However, the provision of habitat walls and bee hotels on  roofs would provide further positive benefits, especially for solitary bees. Further research, though,  is required to really understand the potential for nesting bees on green roofs. The study did include both extensive and intensive green roofs. See the video of wild bees on a rooftop garden here.

There could be a bigger buzz about bees in green roof research?

This is an important addition to global research on wild bees and green roofs. In fact this is the first such study in Central Europe. However, as we have reported already, there is still limited green roof research on this theme. Whilst research on stormwater and other physical aspects dominate green roofs research, there is a paucity when it comes to biodiversity.  Surely bringing nature back to cities is a key driver for green roofs? Although there is a degree of knowledge on the subject, there is a need for more. Bees, bugs and birds do make their homes on green roofs. Let’s hope researchers continue to refine how we deliver better biodiversity up on the roofs of our cities.

IMAGE & ARTICLE SOURCE: Living Roofs