To achieve sustainable urban planning, it is essential to vegetalize urban public spaces. But to know where and under what conditions this approach generates the most benefits, you have to evaluate the cost benefit value of each plant. A conference entitled “Measuring plant value in your city” at Paysalia 2019, summarized below, explained how to make this diagnosis. A must for greening more cities!
What benefits do plants bring?
At this conference, Pauline Laïlle (Plante & Cité) and Anne de Kouroch (AK consultants) explained their approach which consists in assessing each plant’s function to quantify the value it brings. To start a greening plan in your city, you need to have a clear overall concept of what you are trying to do!
Greening cities has many benefits which can be classified using the three pillars of sustainable development:
- Social factors: health, wellbeing, social links, identity, culture, spirituality and connection with nature.
- Environmental factors: thermal regulation, noise attenuation, air quality, biodiversity conservation, water quality and runoff management, carbon sequestration and soil quality.
- Economic factors: valorization of buildings, territorial attractiveness (including using plants to attract tourists), urban farming and the circular economy.
To make the services provided by urban public spaces as sustainable as possible, it is essential to consider all three factors.
How to assess the value of plants benefits in urban public spaces?
This assessment is often complex as the determinants are multifactorial. For example, the social context differs from one community to another. Tourist attractiveness too. The documentation available on the various local plants may be insufficient. This is why each community must make its own assessment, which means that the diagnostic tools described below must be adapted and contextualized.
1. Make an inventory of what already exists
To be able to put a monetary value on plants benefits, you have to understand the system you are studying which implies making an inventory, acquiring knowledge and describing what exists. As far as possible, use local data. If there are none, use national statistics.
2. Analyze the function of each plant
This functional rating must be based on scientific models, in particular by using vegetable physiology. For example, starting from factual data on the number of trees present, their species and the availability of water, it is possible to calculate the plant’s evapotranspiration capacity. This makes it possible to calculate several elements such as carbon sequestration (carbon dioxide removal), the amount of shade, the impact on ambient temperatures in urban public spaces, etc.
3. Assess the function of each plant
It is only after obtaining accurate figures that through the use of several strategies, economic valorization of the contribution of each plant benefit can be made:
- the commercial value (for example, the carbon market)
- the noncommercial value (for example, how much users would be ready to pay to enter a park)
- the costs saved for society (for example, frequent users of green spaces will probably have fewer illnesses)
Some examples of plants benefits valorization in green cities
Several concrete examples of urban vegetalization were discussed at the conference, such as Valuing London's Urban Forest which quantified the value of the millions of trees in London in terms of the various benefits they provide - carbon sequestration, air depollution, rain water management etc.
In a case study, Plante & Cité assessed the value of carbon sequestration by the 16,000 trees in the French city of Angers using the diagnostic tools presented above. Based on a detailed inventory carried out by the public authority, it was possible to quantify the biomass produced each year and the quantity of carbon already sequestered. The forecast for 2030 valorizes this carbon sequestration at 1 million Euros on the European carbon market and 4 million Euros on the national carbon market. A great way to opt for sustainable urban planning!
For more information about assessing the benefits of plants in urban public spaces, Val'Hor and Plante & Cité have jointly produced a guide (in French) which gives more details about this method of analysis and proposes other city greening experience feedbacks. An invaluable help in providing digitized elements for decision makers, enabling them to better plan future public green spaces in their community!
© Crédit photo : magann / Adobe Stock