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

Positive interactions between people and nature inspire behaviours that are in harmony with biodiversity conservation and also afford physical and mental health benefits. Since most people live in towns and cities, urban greenspaces are key points of influence for conservation, but also provide diverse ecosystem services. City trees are a foundation for biodiversity in urban ecosystems, and their belowground interactions with mycorrhizal fungi and aboveground interactions with pollinators must be central to urban ecosystem planning. Messaging about biodiversity must be clearer to avoid unintended negative outcomes from conservation actions such as low diversity tree planting and unsustainable levels of urban beekeeping. Summary: Trees are a foundation for biodiversity in urban ecosystems and therefore must be able to withstand global change and biological challenges over decades and even centuries to prevent urban ecosystems from deteriorating. Tree quality and diversity should be prioritized over simply numbers to optimize resilience to these challenges. Successful establishment and renewal of trees in cities must also consider belowground (e.g., mycorrhizas) and aboveground (e.g., pollinators) interactions to ensure urban ecosystem longevity, biodiversity conservation and continued provision of the full range of ecosystem services provided by trees. Positive interactions with nature inspire people to live more sustainable lifestyles that are consistent with stopping biodiversity loss and to participate in conservation actions such as tree-planting and supporting pollinators. Interacting with nature simultaneously provides mental and physical health benefits to people. Since most people live in cities, here we argue that urban ecosystems provide important opportunities for increasing engagement with nature and educating people about biodiversity conservation. While advocacy on biodiversity must communicate in language that is relevant to a diverse audience, over-simplified messaging, may result in unintended negative outcomes. For example, tree planting actions typically focus on numbers rather than diversity while the call to save bees has inspired unsustainable proliferation of urban beekeeping that may damage wild bee conservation through increased competition for limited forage in cities and disease spread. Ultimately multiple ecosystem services must be considered (and measured) to optimize their delivery in urban ecosystems and messaging to promote the value of nature in cities must be made widely available and more clearly defined.