Living street trees – essential infrastructure for our cities
Humans are amazing at designing things to improve our lifestyles. But, we often neglect that the answers to how to live sustainably are all around us (Janine Benyus).
Unless you are a landscape architect, an environmental engineer, or a particularly enthusiastic ‘greenie’, chances are you don’t think about trees as ‘infrastructure’. But when you look at the number of functions and services trees provide to urban areas, it’s hard not to deem trees as essential infrastructure for our cities.
To check out this comic in high resolution, click here.
What are we referring to? Let’s look at the recent concept known as ‘blue-green infrastructure’. Blue-green infrastructure is the recognition of natural and designed assets in our cities that provide important services for our environment and communities, through the integration of local water management, green space and urban trees. The benefits to our environment and community are wide ranging – providing shade and cooling in hot city landscapes[1], improving air quality[2], improving the amenity and character of streets, increasing soil moisture, improving health and wellbeing of the community[3], assisting with urban biodiversity[2], stormwater treatment protecting our creeks and rivers[4], runoff reduction and detention to alleviate nuisance flooding.
How do you get all these benefits? Some of the benefits are the result of simply providing more greenery (which may not in fact be green!). But for the more nuanced water and ecological benefits, it comes down to something which on the surface is incredibly simple… Connecting green spaces to stormwater runoff. Over time, city and road design has lost sight of the direct and important link between healthy landscapes and water management. We have urban landscapes that are starved of soil moisture requiring significant irrigation to maintain them, and catchments that are suffering from the impacts of increased rainfall runoff frequency and volume.
By combining and protecting the hydrological and ecological values of the urban landscape and recreating a more natural water cycle, we can restore soil moisture while reducing stormwater runoff. One such example of this principle is self-watering street trees.
What are self-watering street trees?
Firstly, let’s look at what might be wrong about this picture:
Using conventional drainage, stormwater runs directly passed our trees.
The tree is also sitting in a very constrained tree pit and sealed surface, which leads to unhealthy trees and limited canopy. Healthy trees rely on the provision of soil moisture to thrive and flourish. And when looking for stormwater quality improvement, vegetated areas play a key role in absorbing, treating and controlling stormwater runoff in urban areas.
So what can we do about it? To start with, re-connect our vegetation with nature’s irrigation source – stormwater runoff. Self-watering trees are designed to capture stormwater runoff, pooling this water and allowing it to infiltrate and irrigate the tree. When coupled with adequate soil volume – a challenge all on its own – this can lead to drastic improvements in the health and resilience of the trees, the size of tree[5], and the resulting canopy.
Want to know more about how to practically implement blue-green infrastructure? Or perhaps looking for ways to integrate these concepts into a coherent plan for your area? Give us a call, or shoot us an email at [email protected]. We’d love to discuss how we can help in getting better outcomes for our trees, communities, and environments. Follow the links below to projects we have recently delivered in this area.
- Embedding Green Infrastructure Best Practice Toolkit
- Infiltration Testing for Permeable Pavement
- Passive Irrigation Modelling in Queensland
[2] Kendal, D., Lee, K., Ramalho, C., Bowen, K., Bush, J., (2016). Benefits of urban green space in the Australian context: A synthesis review for the Clean Air and Urban Landscapes Hub.
[4] https://citygreen.com/blog/controlling-stormwater-runoff-with-trees/
[5] Grey, V., Livesley, S. J., Fletcher, T. D., Szota, C. (2018). Establishing street trees in stormwater control measures can double tree growth when extended waterlogging is avoided, Landscape and Urban Planning, 178, Pages 122-129. doi:10.1016/j.landurbplan.2018.06.002