Bees in the City: Designing Green Roofs for Pollinators

Declining bee populations have been widely covered in the news. It is a pressing issue worldwide as one in three bites of food that we eat relies on bee pollination.

A key factor that affects bees is increasing urban development as people flock to cities. As cities develop, they sprawl into their surroundings, fragmenting animal habitats and replacing vegetation with hard surfaces such as concrete and asphalt. Insects, including a multitude of native bees, rely on soil and plants for foraging and nesting.

Bee habitat and foraging opportunities become smaller and more distant from each other. These segments of green space have become known as “habitat patches,” disconnected pieces of habitat that animals can move between to achieve the effect of a larger ecosystem.

These patches occur in cities and can take the form of ravines, parks, gardens and so on.

Despite the fact that pollinators such as birds, bees and butterflies are better at moving between patches than less mobile species, a continuous habitat is always preferable. Green roofs are seen as a way to make up for ecological habitat fragmentation. But studies and guidelines about where and how to best construct green roofs for pollinators are just emerging.

Though domesticated bee species such as the well known European honey bee (Apis mellifera) tend to receive greater attention when it comes to declining population, wild bee species are often found to be even more threatened. Wild bee species are most commonly “solitary” as opposed to “social” and nest in the ground or in existing cavities, not hives.

Of the 20,000 or so known bee species, 85 per cent or more are solitary. Rapid urbanization, through paving extensive areas of our environment and loss of vegetative cover, is having a widespread harmful impact on their habitat.

Cities are beginning to recognize the importance of creating and enhancing healthy habitats for pollinator populations that support resilient ecosystems and contribute to a rich urban biodiversity.

The City of Toronto is in the process of developing a Pollinator Protection Strategy intended to raise awareness, develop new education and training, evaluate and investment in green spaces, as well as reexamine city maintenance practices.

Green roofs are mentioned in the Protection Strategy as one way cities can compensate for the loss of ecological habitat and provide valuable foraging opportunities for urban wildlife.

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