The state of the world’s urban ecosystems: What can we learn from trees, fungi, and bees?

New publication included in the Kew Botanical Garden's recent State of the World's Plants and Fungi report highlights the role of complex urban ecosystems to stop biodiversity loss.

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Tree in urban area
A flowering tree blooms in the middle of a Sardenian city. Photo: Kalliopi Stara.

The relationship between people and nature is an extremely important one, because positive experiences with nature have mental and physical health benefits and they inspire us to live lifestyles that are more in harmony with biodiversity conservation. So, natural habitats in cities help people to live better and feel better. 

When we think of nature, few think of cities; but actually, urban wildlife is just as important and there is plenty of it, too. Because cities are where most people live, it is here where we need to work hardest to maximise opportunities for people to experience this wildlife in a positive and engaging way. 

Trees are the foundation for biodiversity, especially in cities. They are critical in establishing or regenerating havens of nature in cities, but they also provide many ecosystem services, including cleaner air and water, flood prevention and food. Moreover, they regulate temperature and provide shade, carbon storage and maintain soil health.  We need the right trees to provide these benefits and species able to withstand future shocks and challenges, such as climate change or diseases and pests, over decades and even centuries to maintain healthy urban ecosystems. This requires increased tree species diversity, and not simply trees in large numbers. 

Currently, cities rely on just a handful of species– just 10 common species account for around 40% of urban trees — and so are increasingly at risk. Most tree species are dependent on microscopic fungi known as mycorrhizas, so we need to understand which fungi support which trees, having in mind that mycorrhizal fungi act as carbon sinks in soil. 

Trees also rely on pollinators for reproduction and fruit production and equally pollinators are reliant on trees for pollen and nectar. But, while the honey bee is a fantastic animal and a great way to engage people in conservation, bee-keeping in some cities, like London, is now so popular that it’s unsustainable. The popularity of beekeeping can result in insufficient nectar and pollen available to support the number of kept hives — let alone the other wild bee species which the honeybees are now competing with for food.

With more than half of the world’s population living in towns or cities, urban ecosystems are where the greatest influence can be exerted to focus efforts on stopping biodiversity loss, reversing declines in species and helping people and policy makers understand the multiple benefits of urban ecosystems.

This opinion has been published in the Plants, People, Planet journal and a summary is included in Kew’s fourth State of the World’s Plants and Fungi report, released September 2020. The data included in the report are the result of an international collaboration bringing together 210 scientists from 97 institutions and 42 countries.

Reference

Stevenson Ph, Bidartondo MI, Blackhall-Miles R, Cavagnaro T, Cooper A, Geslin B, Koch H, Lee M, Moat J, O’Hanlon R, Sjöman H, Sofo A, Stara K, M. Suz L. 2020.  The State of the World’s Urban Ecosystems: what can we learn from trees, fungi and bees? Plants, People, Planet 2:482-498. https://doi.org/10.1002/ppp3.10143