Connectivity and flowers help urban pollinators thrive

Of all the impacts human activity on earth has on other species, urbanisation is one of the most profound. Over half of the world’s human population live in towns and cities, and this projected to shift further, to 70% by 2050. This puts pressure on wildlife. There is evidence that mammals, birds, fish, invertebrates and even microbes are affected by the increasing encroachment of our urban areas. To maintain crucial biodiversity, all participants in ecosystems have their roles to play, but many also often provide vital benefits to humanity. There are few groups where this is more pronounced than insect pollinators. Nearly three quarters of crops require pollination by insects such as bees, flies and moths to some extent, but widely-reported declines of pollinating insects threaten the supply of nutritious food, and by extension, human health.

There is a general consensus that increasing urbanisation can have a negative effect on insect diversity and abundance, but it remains a relatively under-studied area, compared to available knowledge on birds and mammals. Pollinators are generally better represented in the scientific literature than other types of insect, however, and there is sufficient evidence to show that urbanisation hits wild bee and butterfly diversity, though outcomes for pollinators also seem to depend on the density of urbanisation. Low-density urban sprawl can sometimes favour them, compared to land used for intensive agriculture.

Urbanisation also has effects beyond simply reducing numbers and species richness. There is a growing body of work suggesting that it affects the behaviour and even physiology of pollinators, in ways that it’s not so simple to predict the long-term effects of. For example, urban life can affect nesting practices, sociality, body size and flight performance, as well pollinator colour. Not only that, but scientists have also shown that urbanisation affects the attractiveness of different flowers, too, undermining plant-pollinator relationships.

Features which allow for connectivity in towns and cities can be helpful. Pollinators need to be able to move effectively between foraging sites, effectively transfer genetic material and find suitable places to rear their young when they do. Scientists have demonstrated that while there’s potential for habitat such as grasslands in urban areas to support pollinators, if they are isolated patches, it is difficult to sustain species diversity. Through analysis of pollen, it’s also been proven that pollinators move between patches of flowers in cities, with them seemingly providing the role of ‘stepping stones’ to larger populations of plants.

Connecting habitat can take the form of ‘corridors’ to encourage effective movement, as well as suitable ‘stopping off’ points and havens around towns and cities. Many landscape features can contribute to the connectedness that pollinators and other invertebrates require. These can include parks, gardens, green roofs, roadside verges and landscape features specially designed to create a corridor effect for species movement. Even roundabouts and stormwater management basins have been shown to potential havens for insect life when handled right, scientists have shown.

Some features can be more effective than others, depending on the type of pollinator. For example, a study in Belgium found that green roofs seem to suit some wild bees, but not hoverflies. Above all, though, it appears that varied and quality of habitat in urban areas is pivotal — and this takes careful management. For pollinators, the amount of suitable flowering plants that are available to them is a crucial factor for their success in urban environments. In some cities, it appears that allotments and cemeteries are providing some of the most beneficial floral resources, while parks are at risk of being ‘over-managed’ to the point of hindering pollinator success.

US researchers have gone as far as to make list of recommendations for the type of resources that urban designers need to incorporate into their plans for cities. Among other points, they called for high densities of flowering plants, including trees, selection of plant species with different flowering times to cover the whole season, as well for the avoidance of wood mulch in favour or bare ground and leaf cover, to provide nesting habitat. Management of common urban vegetation with pollinators in mind is one way to help, while providing nesting sites and municipal authorities reducing grass mowing can also make a difference. To improve gardens’ role as pollinator-assistance, a seemingly simple way of improving success is by using fewer pesticides.

Dedicated projects to add habitat where there was previously none will be needed to maintain and even invigorate pollinator populations in urban areas. The naturetech company 3Bee’s Biodiversity Oases are an attempt to bring increased ecosystem resilience through converting areas of low biodiversity into pollinator-friendly habitat by planting nectariferous trees, introducing managed honeybees and creating refuges for wild pollinators. While many Oases are on degraded farmland, there is also potential for the habitats to be incorporated into urban environments, following the same principles of detailed habitat and biodiversity assessment, tailored regeneration work, communication and reporting. A key advantage of from 3Bee’s work in this area is the collecting of high-quality data on biodiversity.

There are still ‘wildlife friendly practices’ for use in urban areas which are thin on data to back up their effectiveness, meaning this an area where new methods are needed. The Oases established under the project are monitored using the company’s Element- E biodiversity monitoring protocol to record what is known as the Normalized Difference Vegetation Index, or NDVI, which quantifies the greenery in an area. The aim is to achieve continual improvement. With work on 250 sites started in Italy, France, Germany and Spain, there are aims to increase this number to 10,000 in two years.

Moves to improve the quality and connectivity of habitat for pollinators, as well as other animals, in towns and cities are needed, and welcome. Rather than be seen as a problem, it has been said that cities could potentially represent refuges from land managed intensively for agriculture. But urban areas have their own intensities, and there are broader human impacts that need addressing simultaneously. These include chemical, light and noise pollution, the problem of increased temperatures in urban microclimates, as well as the density and materials used in building projects. Change is not going to happen overnight, so needs engagement from policymakers and businesses right now. Ecology is not a ‘one size fits all’ discipline, and there can be unintended consequences, both positive and negative, of human activity. Potential solutions rest in acknowledging this and providing a variety of approaches to help nature thrive. Plant it and they will come.