Cities have long been typified as barren wastelands — concrete jungles inhospitable to plant and animal life. However, the exact opposite may often be true: cities across the globe can be hosts to significant biological diversity.
City biodiversity hotspots
The 34 "biodiversity hotspots" identified worldwide by Conservation International all contain urban areas. Cities containing rich biodiversity are numerous, and they are located in a multitude of geographic locations such as Brussels, Cape Town, Chicago, Curitiba, Frankfurt, Mexico City, New York City and Singapore, to name a few.
Brussels, for example, contains more than 50 percent of the floral species found in Belgium. Cape Town is host to 50 percent of South Africa's critically endangered vegetation types and approximately 3,000 indigenous vascular plant species.
Singapore has more than 10 ecosystems within its bounds and recent surveys have recorded more than 500 species of plants and animals new to Singapore, of which more than 100 are new to science.
Professor Thomas Elmqvist, a researcher at Stockholm Resilience Centre, discusses this trend in the world's first global assessment of the impacts of urbanization on biodiversity, produced under the aegis of the UN Convention on Biological Diversity (CBD).
Elmqvist is the scientific editor of the project, the Cities and Biodiversity Outlook (CBO). Since 2010, the Convention's 193 Parties have adopted a Plan of Action to involve cities in its implementation. The Cities and Biodiversity Outlook will provide policy advice in the urban context.
"Cities are often very rich in biodiversity, and that is because they were located in very rich areas, in floodplains and in low areas with high fertility," says Elmqvist.
"So naturally, you would have very high diversity of plants and animals. Now, cities need to learn how to co-exist with that biodiversity."
A multitude of opportunities
Many of the urban areas located in biodiversity hotspots are notable in population and geographic size. These cities and their path of future development will be critical to the persistence of rich biological resources and the crucial ecosystem services provided for urban populations. Such ecosystem services include food, water, protection from natural disasters, protection from a changing climate, as well as support for health and wellbeing.
It is not just cities with large, intact natural ecosystems that are important: With global urban land expansion over the next 40 years predicted to encompass an area the size of Mongolia, remnant natural patches, restored ecosystems and managed green spaces will all become increasingly critical as refuges for biodiversity.
What to do
Nearly any city can create interventions that enhance biodiversity. Connecting fragmented ecosystems is a particularly useful strategy to increase ecological function. This can be achieved through planting trees to expand the tree canopy, establishing corridors of multilayer plantings along roadsides and verges, as well as introducing ecolinks such as tunnels and vegetated overpasses.
Cities can also focus on improving and restoring their existing green spaces to draw increased attention to local biodiversity. Planning, design and management of urban areas are integral to maintaining as well as enhancing biodiversity and ecosystem services.
"The way our cities are designed, the way people live in them and the policy decisions of local authorities will define, to a large extent, whether the ambitious 20 targets of the Convention's Strategic Plan will be met in 2020", says Braulio Dias, Executive Secretary of the Convention.
"National governments need the support of cities, and the CBO will help us get there."
A Tool for management
Monitoring and evaluation is fundamental to understanding the impacts of biodiversity management. One tool that can assist is the Cities and Biodiversity Index (CBI), a self-assessment inventory that enables cities to track their progress related to conserving and enhancing biodiversity using 23 indicators. The use of the Index is described in the CBO.
"Results from the CBI can be used in the decision-making and master planning of cities to allocate resources and prioritize projects," Elmqvist remarks.
"Ultimately, identification of successful practices and projects can help to provide case studies for sustainable development."
See video with Thomas Elmqvist explaining the many links between urbanization, biodiversity and ecosystem services: