Fancy gardens bring all the bees to the yard

A large-scale study of floral resources and pollinators in 360 sites in four major British cities is published online this week in Nature Ecology & Evolution.

Although urbanization threatens pollinating insects like bees and hoverflies, previous small-scale studies have indicated that some parts of cities might support substantial pollinator populations. Identifying how different types of urban land use affect pollinators could help develop more biodiversity-friendly cities to slow declines in bees and other such species.

Katherine Baldock and colleagues surveyed the distributions of plants and pollinating insects in Bristol, Edinburgh, Leeds and Reading. They examined how these distributions differ among nine major land-use classes: cemeteries, community gardens (also known as ‘allotments’), manmade surfaces, nature reserves, other greenspaces, parks, residential gardens, road verges and sidewalks.

The authors found that residential and community gardens support higher pollinator abundances than the other classes of urban land - with up to 50 times more bees than areas with manmade surfaces, such as car parks and industrial estates. They attribute this difference to variations in flower diversity. Similarly, residential gardens of higher-income households, which typically have greater floral resources, attracted more pollinators.

The authors simulated how plant-pollinator communities would change under different urban planning schemes. They find that enlarging community gardens, increasing the number of flowers in parks and roadside verges, and enriching greenspaces in poorer areas would all be simple and effective strategies for pollinator conservation in cities.