Why biodiversity is important for cities

Examples of fauna using plants for resources in green spaces (caption and credits below)

Authors: Alessandro Ossola and Samiya Tabassum, June 25^th, 2021

Urban biodiversity is all around us. Outside your window right now, all the plants, insects, birds, down to minute micro-organisms in the soil, work together to ensure that urban ecosystems work according to nature’s plans. Urban biodiversity and nature provide urban communities with many tangible benefits; people living in biodiverse suburbs feel happier and less stressed; urban ecosystems that mimic natural ones are more resilient to climate and environmental changes (Ossola & Niemelä, 2018). While urban biodiversity generously takes care of us behind the scenes, we can all make a contribution to help our ‘neighbors’ thrive in our buzzing cities.

What urban biodiversity does for you

Scientists are starting to understand and appreciate the many benefits that urban biodiversity provides for our cities and towns. Kids who play in nature-like environments, and touch plants and soil, develop less allergies and have better health when adults. Their parents feel more relaxed when they walk and exercise in biodiverse neighborhoods and parks. The elderly have lower risk of stroke, recover faster from hospital, and experience relief from dementia, when they live surrounded by green and diverse urban nature. Biodiverse streets have been linked to lower use of antidepressants (Marselle et al., 2020). In some countries, like New Zealand, “nature-prescriptions” can now be issued by medical doctors; the ultimate recognition that urban biodiversity can be an effective public health strategy much needed in our crowded cities.

Diverse urban plantings mean more biodiversity

Urban plants such as trees, shrubs and herbs, can provide food and habitat resources for a range of interesting insects, birds, reptiles and mammals. However, it is often not enough to just fill an urban space with the same plant species because most fauna require a variety of plant species for food and shelter. Unfortunately, the diversity of plants used in urban settings is often much lower than what is found in native vegetation. Therefore, some thought is needed when planning an urban space to help attract a diverse range of native fauna. For example, urban green spaces that are made up of plants of different ages and canopy heights have been shown to attract a greater diversity of native fauna compared with non-diverse plantings. Furthermore, using a diverse set of plants in urban greening projects ensures that food resources such as nectar, pollen and fruits/berries are available for native fauna throughout the year, thus increasing the usability of the urban green space.

Giving urban biodiversity the best chance!

Everyone can contribute to ensure that urban plantings help the numerous groups of animals and wildlife thriving in cities. Whether you are an avid gardener tending a small backyard, an experienced landscape architect designing a new neighborhood or an urban forester in charge of a large urban forest, here are some tips to guide your efforts:

The more diverse the merrier. Scientists think that having higher biodiversity contributes to better ecological outcomes for cities and towns. While some organisms and species might have similar ecological roles, having many of them is like our “ecological insurance” where – if one disappears – all the others can still properly function in the urban landscape.
Creating a ‘connected’ urban landscape. Just because you plant the right plant species at the right location, it does not necessarily mean that all the intended biodiversity groups will come right away. It is important to think about the larger landscape context around your project. What are the barriers that impede ecological connectivity? Can you think about alternatives and additional plantings that can facilitate the connection of green patches across the city?
Think ahead! Plants take time to grow; an urban forest needs decades to thrive. You can select species based on their growth rates to create an “ecological succession”, where fast-growing species can kickstart building the green infrastructure, while other slow-growing and long-lasting species take their time to grow to maturity.
Mix diverse species and life forms. Plant diversity is not only about species, but also about their form, shapes and sizes, that make up a complex and rich habitat. Research suggests that diverse urban plantings composed by many cultivars and species from different life forms and multiple vegetation layers offer the best opportunities and resources for many groups of animals and wildlife. Plants are so versatile that there are endless combinations possible to design a complex and appealing landscape.
Acknowledge nature’s rhythm. Plant species should be chosen based on the timing when they will provide the resources needed by the biodiversity groups you want to help. Also known as phenology, plants produce leaves, flowers, fruits and seeds at specific points in time that must be matched to suit the organism potentially using these resources. If you have a butterfly visiting a specific flowering plant for its nectar, but the flowers are produced when the butterfly is still a caterpillar, then that choice of plant species will not be helpful in supporting the butterfly species.
The native or exotic debate. Native plant species are often seen as more beneficial to native fauna compared to exotic plants. However, many exotic species that do not pose an ecological threat (i.e., are not considered to be weeds, or invasive) may still have value for wildlife and in creating greener and more sustainable cities. Many species of exotic trees, almost extinct in the wild, still call some cities their home and are a valuable resource for conservation (Ossola et al., 2020).
Nature with people. Urban biodiversity is the most direct experience of nature for most people. This provides the opportunity to increase environmental awareness among communities, including stewardship and care. Planting a tree is not just about greening, it is a commitment to a better future and a legacy that future generations will benefit from.

Banner image: Native lizards, such as the eastern blue-tongue skink (Tiliqua spp.) often use vegetation to shelter from the hot sun (photo credit: WShipway, Wikimedia Commons). Native birds, such as galahs (Eolophus roseicapilla) commonly nest in urban trees (photo credit: Nina Matthews, Wikimedia Commons). Native insects, such as blue banded bees (Amegilla spp.) visit plants such as the native hibiscus (Alyogyne hakeifolia) to collect food (photo credit: Jean and Fred, Wikimedia Commons). Native mammals, such as brushtail possums (Trichosurus vulpecula) frequently feed on fruits from trees planted in urban spaces (photo credit: Christopher Watson, Wikimedia Commons).

REFERENCES

Ossola, A., Niemelä, J., 2018. Urban Biodiversity: from Research to Practice. Routledge, London and New York. ISBN: 9781138224391.

Ossola, A., Hoeppner, J.M., Burley, H., Gallagher, R.V., Beaumont, L.J., Leishman, M.R., 2020. The Global Urban Tree Inventory: A database of the diverse tree flora that inhabits the world’s cities. Global Ecology and Biogeography, 29:1907-1914. https://doi.org/10.1111/geb.13169