Against the odds, cities host an incredible array of flora (vegetation) and fauna (animals). How can we ensure that they thrive and why should we bother?
Biological diversity – more commonly shortened to biodiversity – is a collective name given to all living organisms. Most of them will be one of the following:
- Flora – plants, grasses, trees, mosses, lichens, and flowers
- Fauna – mammals, marsupials, birds, fish, amphibians, reptiles, insects, molluscs, annelids (e.g. worms), arachnids (such as spiders), and crustaceans (like crabs)
- Fungi – mushrooms, toadstools, mould, yeast, and truffles
- Monera – algae and single cell organisms like bacteria and viruses
- Protista – other microscopic life forms
Humans – mammals – represent relatively little of all life on the planet. We’re increasingly living closer together in cities, similar to ants in their nest and bees in a hive.
In 2020, cities only occupied around 3% of the earth’s surface but urban sprawl is accelerating to accommodate our growing population’s need for housing, amenities, and public spaces. A decade has already passed since built up areas were growing by 1.16km2 every hour – urbanising natural or rural land equivalent to the size of Paris every five days.
Does this really matter, and if so, what can we do to improve the stakes for biodiversity while still meeting the needs of citizens?
What is Urban Biodiversity?
While biodiversity is a universal term for all living organisms, the World Wildlife Fund defines urban biodiversity as any species that has adapted to co-exist “in and around dense human settlements,” whether that be on land, in water, or circling the skies above us. About all it doesn’t include is captive species in zoos and domesticated animals like pets and livestock.
There’s a distinction between wildlife and biodiversity. Wildlife is an umbrella term reserved for animals, whereas biodiversity also covers vegetation and other non-animal life forms.
And cities are teeming with it! As the Yale School of the Environment makes clear, “cities contribute more than we think to regional biodiversity,” adding that urban sites are “important refuges for an array of plants and animals, in some cases even threatened and endangered species”.
This promising, but there’s a dark side to it too. As human’s change the natural world to suit our needs, we reduce the amount of natural land available to biodiversity, so they have little choice but to adapt or die out. Roads, buildings, manicured gardens, and agricultural fields hem species in to smaller and smaller spaces and cut off the routes they take to move between places.
What species we see in cities obviously differs from place to place, but there are plenty of examples common to cities across multiple continents:
- Tree trunks of municipal parks and urban forests make ideal habitats for insects, small vertebrates, and birds
- foxes that rummage through your bins at night
- fish and ducks that inhabit urban streams and ponds
- rats that one can occasionally glimpse scurrying along a gutter
- wildflowers and grasses that make up urban meadows and roadside verges
- plants displayed in pots and hanging baskets on balconies – and the bees that pollinate them
- bats that swoop in hunt of flying insects at dusk
- birds which we invite to eat from tables in the garden – and the squirrels that maybe we don’t
- climbing plants that adorn outside walls
- worms, mushrooms, and ants that aid decomposition of dead leaves littering the ground.
Biodiversity as Sanctuary
The species we see inside and beyond the city limits may be the same, but the environments they inhabit can alter behaviour – especially for animals.
Urban species have adapted to the unnatural structures that humans have built, swapping nesting on the cliff face for the façade of an office block, for example, or bats hanging around in wall cavities.
Then there are the species that we (re)introduce: Vancouver, Canada, put a series of large trees like horse chestnut, oak, and beech in parks to soak up stormwater; Leicester, UK, has increased the presence of grassland to act as a carbon sink; and beavers have been successfully reintroduced to London, UK.
Public Buy-in
It’s worth saying that not all green space is equal. It’s not even all natural.
Gardens have a part to play in the success of urban biodiversity: they provide a source of shelter and food and, if close enough together, can provide a corridor for animals to hop from one blue-green space to another.
Lush, well-kept lawns may look good when weed-free and tightly mown, but they fall short of what wildlife needs.
It’s often a single species of grass, which is not inviting to a spectrum of living creatures. Chemical weed killers keep it that way. For the limited amount of life these types of spaces can sustain, manicured gardens, sports pitches, and playing fields more closely resemble deserts.
Having said that, it is important not to demonise these spaces. They provide much-needed amenities to citizens; they should just not be the standard model of greenspace management.
Why Does Urban Biodiversity Matter?
Cities may be built primarily for people, but biodiversity is a linchpin to how they function.
It’s easy to forget that, like any species, humans have a place in the natural ecosystem. But even the synthetic systems which we have built – e.g. international food chains – are dependent on wildlife: key species like bees pollinate crops and sustain the food sources which we eat.
More than 75% of global food crop types rely on animal pollination
EU Biodiversity Strategy for 2030
Naturalise spaces are advantageous to people’s quality of life, and there’s a need to make more. According to the UN, only 40% of the world’s city-dwellers can easily access green and open public spaces like a park or playground. Yet, it continues, these are “crucial” for wellbeing because they create opportunities to “promote physical activity, mental wellness, social interactions, and community engagement”. Biodiversity even correlates with reduced stress levels and quicker recovery rates among hospital patients.
A Long List of Benefits
Urban biodiversity serves plenty more purposes that directly benefit us:
- Pollinators such as beetles, moths, hoverflies, mosquitoes, butterflies, bats, and wasps fertilise the flowers which beautify our streets and homes
- Through respiration and taking up fluids, vegetation filters impurities in the air and waterways, reducing the health risk of pollution
- Songbirds fill a city with their enchanting calls
- Making room for larger predators is a natural population control for smaller animals, including species that can be dangerous to human health (e.g. mosquitoes and scorpions)
- Flora is effective at mitigating flood risks by drinking up stormwater – an advantage more cities are recognising because of an uptick in extreme weather events
- Roots of all kinds of vegetation stabilise soil too, preventing erosion (which can cause more flooding) and dangerous mudslides
- Bacteria in soil helps break down dead material, releasing nutrients that feed the next generation of plants, trees, and – in the case of urban farming – even fruit and vegetables
- Biodiversity-rich landscapes are fun for children to play in and learn about the natural world
A Robust Line of Defence
Biodiversity is even an ally in the way we adapt to and mitigate the effects of climate change.
For example, biogas is a low-carbon alternative to fossil fuels, and it turns out that worms, rats, and microbes are the unseen champions of creating it from urban wastewater.
In a phenomenon known as the Urban Heat Island effect, streets of asphalt and concrete trap warmth making cities on average hotter. Evapotranspiration from greenery offers respite by cooling the immediate vicinity.
Pigeons, raccoons, and rodents often clean up food left in the street or in bins, preventing waste from going to landfill where it would break down and add to greenhouse gases.
As we’ve learnt from Leicester, diverse urban grasslands are an incredibly effective carbon sink, as mosses, lichens, shrubs, wildflowers, and especially grasses suck in CO2 and trap it in living matter as they grow.
If none of these reasons convince influential types that biodiversity matters, there’s one more argument that could change their tune: money.
Urban biodiversity is a cornerstone of the economy: from professionals in food supply chains to engineers who construct green roofs, through municipal park maintenance staff, and experts in animal protection, there is a huge, thriving, and ever-growing industry connected to the natural world. It’s thought that as many as 59 million decent, stable green jobs could be created by 2030, just by restoring biologically diverse land.
The Many Challenges Facing Urban Biodiversity
Biodiversity must form part of the strategy we employ to reverse a 60% decline in wild fauna that has taken place in the last 40 years, a situation where 16% of vertebrate pollinators – birds and bats – and 40% of species like bees and butterflies (or invertebrate pollinators) are on the verge of extinction.
The climate crisis is not the biggest contributor to this decline in biodiversity. Human uses has severely degraded three-quarters of land on the planet through activities like habitat destruction and liberal use of chemical pesticides.
Which raises an important point: the preservation of urban biodiversity is not only about giving wildlife a space to live; it’s about encouraging the very species that are inner city habitats, like grasslands and urban forests. These must be places of sanctuary for species to feed and breed free of risk from human interference, insecticides, and invasive species. That requires a general change to how we manage urban land use. We also need to be open to the idea of “scruffy” naturalised spaces; patches left fallow for nature to take root.
It’s not an easy ride. Often where people and wildlife mix, there is conflict. Pigeons have adapted very well to urban environments, to the dismay of many who dislike the mess they leave. Other species are emboldened and can get aggressive as they become increasingly dependent on humans: seemingly tame squirrels in the park can leave a nasty bite if startled.
And sometimes a species will thrive beyond our intentions. In the USA, zebra mussel populations have boomed, clogging pipes as efforts were made to welcome and protect other underwater life.
Practical Actions for Cities
When the public is used to seeing their surroundings well-kept, it can be difficult to bring the consensus on board with the “messier” appearance of a wild, naturalised, biodiverse cityscape.
The one quick win is wildflowers, because people are generally satisfied with how pretty they look.
Otherwise, municipalities can lean into education and communication strategies to raise awareness of biodiversity, to normalise its presence – in all its forms – in urban centres, and to justify any methods the city employs to promote it.
Marketing strategies can be costly, and this would be no exception, but that’s nothing compared to the price we’ll pay if we fail to conserve urban biodiversity in all its wonderous forms.