Written by Emma Bock - Editor: Anastasia Eginoglou
Trees. There are so many reasons to love these beautiful plants, especially in our cities. As the effects of climate change increase, cities are adding trees to their urban fabric to provide relief. Trees provide Urban Heat Island relief, improve air quality, manage stormwater, and improve people's overall well-being in urban centres. As trees become recognised as valuable tools to create resilient urban forms, cities are implementing strategies to increase their canopy coverage.
First, let's discuss why trees are so valuable in combating the effects of climate change. As temperatures continue to increase, the thermal comfort in cities dwindles as the materials we construct with retain heat, increasing the actual temperature in city centres. This effect is known as the Urban Heat Island effect, and with the average temperature only growing with the ongoing climate crisis, it will only worsen. Trees can alleviate these elevated temperatures by increasing shade and cooling the air through a process called evapotranspiration. Evapotranspiration is when the water taken up through the tree is later released as water vapour during photosynthesis. This water vapour helps cool the surrounding air, providing a much more comfortable environment during peak heat.
Along with rising temperatures, we also see increased precipitation and rainfall intensity. These conditions, mixed with hardscapes of concrete and impermeable surfaces, create more stormwater runoff rushing down our streets and sidewalks into our sewer systems. Trees require open surfaces for roots to take in water and oxygen, so when we plan for more trees in our urban design by-product, we plan for more permeable surfaces, which help alleviate the stormwater runoff. Urban vegetation, such as trees, can lessen the stress of runoff by retaining water in its soil and intercepting rainfall with its canopy, slowing the rate at which rain hits the ground.
Trees are also a great tool to help filter out the pollutants found in our cities, especially CO2. The current way we design our cities creates high-density scenarios that interfere with airflow, trapping pollutants such as CO2 in our everyday spaces, and with more people expected to live in urban centres in the years to come, CO2 levels are expected to increase. Planting trees can help eliminate these pollutants because excess CO2 can be used in the tree's photosynthesis process, which is required for growth. Planting more trees to take in some of the CO2 levels helps offset the increasing levels we can expect soon.
Lastly, several studies have shown that trees can provide mental and physical health benefits. Green space or even green views help reduce stress, anxiety, and depression, and accessible green infrastructure, such as green corridors and urban parks, encourages active transportation and recreation, providing inhabitants with a healthy, active lifestyle in dense areas. There is no doubt that trees provide numerous benefits for our urban centres, so isn't it the most straightforward solution to creating a climate-resilient city? Let's all plant a tree and create a sustainable city! Unfortunately, it's not that easy. Just like urban areas cause stress to our human livelihoods, urban areas can wreak havoc on trees. The abundance of impermeable surfaces, the compact soil, and the lack of space all contribute to whether a tree will live a happy life. These harsh urban conditions make it extremely difficult to incorporate trees into our urban fabric. How do we move forward? What type of guidelines should we follow? How many trees should we plant? These are all questions urban designers and city planners have, and thanks to Cecil Konijnendijk, a principle known as the 3-30-300 was created.
The 3-30-300 principle provides guidance for cities to improve their urban forests through thoughtful urban design and planning. The principle focuses on green views, green living, and green space – one should be able to view 3 established trees out any window, live with no less than 30% tree coverage in their neighbourhood and be no more than 300 meters away from a green public space. These three guidelines are suggestions and a roadmap for cities to follow in their quest for urban sustainability. They are a testament to the importance of thoughtful urban planning and the role of trees in creating healthier, more livable cities. Many cities are now recognising the value of a strong urban forest. Urban forest in their city and have created strategies to implement the 3-30-300 principle.
Melbourne, Australia, is a city that used the 3-30-300 principle as inspiration to create a climate-resilient city that provides thermal comfort for its inhabitants. The city has been dealing with catastrophic heat waves in the summer months, leading to heat-related illness and death among civilians. The city has come to terms with how its current urban form does not support a healthy city for its residents and that something needs to change, and with this came the tree-planting strategy. The city is using the 3-30-300 principle as guidance and has pledged to plant many more trees. In 2012, the city released their plan to cool the city by 4 degrees Celsius by 2040 by increasing its canopy from 22% to 40%. The city has created a comprehensive design guide to ensure that new development and redevelopment include the correct number of trees to meet its goals. Currently, the city is moving strongly in its strategy, with more than 80,000 trees planted and 32 major street tree projects completed. With the ongoing progress, it will be interesting to see how the city evolves over the coming years as we get closer to the goal year of 2040.
Here in Copenhagen, the city has committed to increasing its canopy in the coming years; however, it is the Frederiksberg Kommune within Copenhagen that is directly using the 3-30-300 principle. You can even experience the difference in the canopy yourself. As soon as you cross over from Copenhagen into Frederiksberg, you'll notice many more street trees, and this is solely due to the implementation of the 3-30-300 principle. Since the Kommune has incorporated the 3-30-300 principle into its tree planting strategy, all future development within the Kommune must follow the principle's guidelines. One current example is the new hospital development, which is committed to planting an adequate number of trees. The Kommune is also striving for better green views and has worked hard to make sure all residents can see at least one tree from their window. They have achieved this by ensuring that existing trees are maintained and by planting more trees on streets. Now, Copenhagen may not show the same determination as Frederiksberg when it comes to implementing the 3-30-300 principle. Still, they are making strides, and with a neighbouring kommune like Frederiksberg showing how to integrate the principle in planning, Copenhagen has a great example to follow.
While Melbourne and Frederiksberg show great initiative, Singapore is another example of a city that uses trees as green infrastructure to improve its resiliency. A study discovered that Singapore is one of the few cities that meet the 30% canopy goal included in the 3-30-300 principle. Seeing a city like Singapore successfully incorporate urban forestry into its city planning is a testament to what is possible in our urban centers. Hopefully, with the success of the work from Melbourne, Copenhagen, and Frederiksberg, we will have many more cities meeting the 30% canopy coverage goal.
These three examples are just a few of the cities that have adopted similar strategies to the 3-30-300 principle to prepare for the ongoing battle against the climate crisis. Other cities have also implemented similar strategies to increase their urban tree canopy, combating the Urban Heat Island effect and creating a climate-resilient city. Seeing so many cities take tree planting seriously in their urban planning is inspiring. Trees offer a multitude of valuable benefits, and they need to be integrated into our cities. The 3-30-300 principle provides the necessary guidance to create climate-resilient cities using trees, and its inclusion in city planning signals a shift in our approach to urban design. The next time you walk in your city, take note of your own urban forest. How does your city measure up to the 3-30-300 principle?
References:
Croeser, T., Sharma, R., Weisser, W. W., & Bekessy, S. A. (2024). Acute canopy deficits in global cities exposed by the 3-30-300 benchmark for urban nature. Nature Communications, 15(1). https://doi.org/10.1038/s41467-024-53402-2
Fleetwood, J. (2024, July 24). City of Melbourne unveils next Urban Forest Plan for the CBD. CBD News. https://www.cbdnews.com.au/city-of-melbourne-unveils-next-urban-forest-plan-for-the-cbd/
Frederiksberg Kommune. (2022, June). FREDERIKSBERG HOSPITAL. Frederiksberg Kommune. https://www.frederiksberg.dk/media/jqid2uye/frederiksberg-hospital_vurderingsrapport-webtilgaengelig_low_2.pdf
Frederiksberg Kommune (2024). Frederiksberg’s City Strategy 2024: A great life in a green, diverse city. Frederiksberg Kommune. https://www.frederiksberg.dk/media/i4rp4nn2/frederiksbergs-city-strategy-2024.pdf
Livesley, S. & McPherson, G. & Calfapietra, Carlo. (2016). The Urban Forest and Ecosystem Services: Impacts on Urban Water, Heat, and Pollution Cycles at the Tree, Street, and City Scale. Journal of Environment Quality. 45. 119. 10.2134/jeq2015.11.0567.
NBSI. (n.d.). 3-30-300. Nature Based Solutions Institute. https://nbsi.eu/the-3-30-300-rule/