Urban street trees / transport and infrastructure corridor planting 

  Franklin Road’s trees form a full canopy of protection over the road. Auckland, Aotearoa New Zealand. Photo from Bike Auckland.

.Urban street trees and transport/infrastructure corridor planting are simple but very effective nature-based solutions for combatting the effects of climate change in urban areas. The strategy is to plant and care for trees in public spaces in cities, and specifically along roads, motorways and other transport corridors. Urban areas with green cover, trees, and landscaping are often more resilient to the negative effects of climate change. Trees improve air quality, reduce the urban heat island effect, and can provide some disaster risk reduction (Tyrväinen et al., 2005).

Interaction with the natural world is good for people’s physical and mental health (Pedersen Zari, 2023), so cities with urban trees improve both human and ecosystem wellbeing. Added to transport corridors and busy streets, trees offset polluting effects of vehicles. Te Moananui Oceania states, territories, and nations are generally characterised by lush greenery. The inclusion of trees in urban environments is a way to reflect typical ecologies. 

Name of NbS

Urban street trees / transport and infrastructure corridor planting

Type of NbS

Hybrid living/engineered interventions

Location

Urban

Tagabe river bank planting. Photo from SPREP

Relationship to Indigenous knowledge

Indigenous knowledge hinges on a reciprocal relationship with the natural world. As Pacific peoples become increasingly urbanised, there may be a loss of that connection (Rodgers et al., 2023). Strategic species selection of urban street trees may be a way to address that issue.

Protection of existing urban street trees as cities develop may be a way to preserve native species and ecologies and indigenous knowledges bound to those.

Climate change benefits
  • Changes in phenology
  • Changes in rainfall
  • Coastal erosion
  • Coastal inundation 
  • Desertification
  • Drought 
  • Increased temperatures
  • Increased incidence / distribution of disease
  • Reduced air quality
  • Wind/storm damage
  • Urban heat island effect

Humans are becoming increasingly urban and cities are particularly susceptible to climate change. Rising temperatures and drought increase energy demands to heat and cool buildings and put pressure on public health systems. Temperatures are further intensified by the urban heat island effect, and stormwater infrastructure not designed to handle increased rainstorm events (Bühler et al., 2012). Urban street trees help to combat the urban heat island effect by increasing biomass and canopy cover, though the relationships of cause and effect in this regard are complex (Sanusi et al. 2016). 

A large majority of plants rely on pollination to reproduce (Barbour et al., 2021). Urban trees can provide biodiversity corridors and pollination pathways, that allow birds and insects to move through cities.  

Motor vehicles and industrial processes are major contributors to air pollution. Six major air pollutants are particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead (Balali-Mood et al., 2016). Exposure to these pollutants can have significant impact on human health, including respiratory and cardiovascular diseases, skin diseases and long-term chronic illness (Balali-Mood et al., 2016). Trees along transport and infrastructure routes are especially useful because they act to reduce, capture, or transform significant amount of pollutants produced by vehicles. Trees store carbon dioxide and remove pollutants from the air (The Forest Preserve District of Will County, 2024). 

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Societal / socio-cultural benefits
  • Disaster risk reduction and resilience
  • Human physical health and wellbeing

Connection to the natural environment is critical in supporting good mental health and preventing distress. Research shows that people who are more connected with nature are usually happier, and more likely to have pro-environmental behaviours. The research also shows that communities deprived of green space or access to nature are more at risk of mental health problems (Kondo et al., 2018; Nutsford et al., 2013). Increasing the amount of trees in areas of lower socioeconomic status is therefore essential to support all members of our communities and address access to nature justice issues (Wolch et al., 2014).

The aesthetic value of trees and green spaces is undeniable. Along transport corridors, characterised by harsh, hard materials, trees add a softening element. On urban streets, trees provide shade and shelter to pedestrians, creating nicer places to walk.

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Ecological and biodiversity benefits
  • Climate regulation
  • Disturbance prevention
  • Habitat provision
  • Pollination
  • Species maintenance

In Te Moananui Oceania, as natural environments including trees are removed to build roads and new neighbourhoods, keeping and protecting urban trees, including mangroves can be a way to create and enhance resilience. New trees should be implemented into infrastructure and urban design projects where possible. Trees provide habitats for birds and insects, maintaining species populations and supporting pollination. Trees are a life support system for plants, animals and humans. They protect land from erosion, can build soil and keep air, streams and lagoons clean. They are also a source of food (Thaman & Whistler, 1996).

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Trees along transport corridors and roads help to mitigate pollutants. Photos from NZTA

Technical requirements

In Te Moananui Oceania, there are greatly varying levels of protection for existing urban trees, especially native species. The care for urban trees often falls to Councils or independent organisations. Some Governments in the region (such as in Tararwa in Kiribati) have been actively removing urban trees as a response to preventing damage caused by trees falling in increasingly intense storm events. These trees might be replaced with flowers and shrubs or paving. It is vital that policymakers understand the value of urban trees to prevent soil loss, reduce temperatures, provide food and shade, and contribute to stormwater management.

Issues and Barriers

Small areas for root growth, and sealed surfaces in towns and cities can be a harsh environment for an urban tree, so care must be taken to ensure they have enough space to grow, species are carefully selected, and that they are properly looked after. Where trees are contained in small spaces, there may be insufficient space for root expansion. Compacted or degraded urban soils soil may restrict water and nutrient absorption. It is vital to plan for trees at the beginning of urban design projects as retrofitting trees into urbanscapes is not impossible but can be more difficult.

Opportunities

There are opportunities across Te Moananui Oceania to utilise the often tropical or semi-tropical environments, which correspond with lush, fast growing vegetation often, to combat the effects of climate change. Reintroducing trees to urban contexts, and protecting the trees that do exist already, provides a key range of benefits to humans and the natural world. Introducing more trees can be a clear starting point for cities seeking to increase climate change resilience and adaptation.

Oceanic nations are already realising the need for more urban street trees. Fiji, Samoa, Vanuatu and Nuie have planting programmes in place. In Port Vila, The Secretariat of the Pacific Regional Environment Programme (SPREP) and Vanuatu’s Department of Forestry launched an urban forestry programme aiming to intensify tree planting and increase people’s understanding of the propagation of tree crops (SPREP, 2018).

There are opportunities to work with community organisations, to create education and training programmes, and to make cities more enjoyable to live in with the inclusion of more urban trees.

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Financial case

Urban street trees provide climate change resilience, improve the health and wellbeing of people and ecosystems, and can be natural food sources. There is a strong financial case for planting more urban trees because it is a reasonably inexpensive way to improve our cities and the lives of people who live in them. The financial case for urban street trees is very site specific as discussed and illustrated by Killicoat et al., (2002).

The benefits of urban trees. (Image by Miriam Brune/GERICS):
References
  • Fryd, O., Pauleit, S., & Bühler, O. (2012). The role of urban green space and trees in relation to climate change. CABI Reviews, 1–18. https://doi.org/10.1079/PAVSNNR20116053 
  • Ghorani-Azam, A., Riahi-Zanjani, B., & Balali-Mood, M. (2016). Effects of air pollution on human health and practical measures for prevention in Iran. Journal of Research in Medical Sciences, 21(1), 65. https://doi.org/10.4103/1735-1995.189646 
  • Killicoat, P., Puzio, E., & Stringer, R. (2002). The economic value of trees in urban areas: estimating the benefits of Adelaide’s street trees. In Proceedings Treenet Symposium (Vol. 94, p. 106).
  • Kondo, M. C., Fluehr, J. M., McKeon, T., & Branas, C. C. (2018). Urban green space and its impact on human health. International journal of environmental research and public health, 15(3), 445.
  • Nutsford, D., Pearson, A. L., & Kingham, S. (2013). An ecological study investigating the association between access to urban green space and mental health. Public health, 127(11), 1005-1011.
  • Pedersen Zari, M. (2023). Understanding and designing nature experiences in cities: A framework for biophilic urbanism. Cities & Health, 7(2), 201-212.
  • Planning and Urban Management Agency. (2018). Urban Design Standards: Apia Central Business District (CBD) and Waterfront Areas. https://www.mwti.gov.ws/wp-content/uploads/2022/09/Apia-Urban-Design-Standards_Final.pdf 
  • Rodgers, M., Mercier, O.R., Kiddle, R., & Pedersen Zari, M. (2023). Plants of place: justice through (re) planting Aotearoa New Zealand’s urban natural heritage. Architecture_MPS, 25(1).
  • Sanusi, R., Johnstone, D., May, P., & Livesley, S. J. (2016). Street orientation and side of the street greatly influence the microclimatic benefits street trees can provide in summer. Journal of environmental quality, 45(1), 167-174.
  • Secretariat of the Pacific Regional Environmental Programme (SPREP). (2018). Urban forestry project commences in Port Vila, Vanuatu. https://www.sprep.org/news/urban-forestry-project-commences-in-port-vila-vanuatu 
  • Thaman, R., & Whistler, A. (1996). A Review of Uses and Status of Trees and Forests in Land-use Systems in Samoa, Tonga, Kiribati and Tuvalu with Recommendations for Future Action. https://www.researchgate.net/publication/350358072_A_Review_of_Uses_and_Status_of_Trees_and_Forests_in_Land-use_Systems_in_Samoa_Tonga_Kiribati_and_Tuvalu_with_Recommendations_for_Future_Action 
  • The Forest Preserve District of Will County. (2024). Nature curiosity: How do trees clean the air? The Buzz. https://www.reconnectwithnature.org/news-events/the-buzz/nature-curiosity-how-do-trees-clean-the-air/ 
  • Tyrväinen, L., Pauleit, S., Seeland, K., & De Vries, S. (2005). Benefits and uses of urban forests and trees. Urban forests and trees: A reference book, 81-114.
  • Wolch, J. R., Byrne, J., & Newell, J. P. (2014). Urban green space, public health, and environmental justice: The challenge of making cities ‘just green enough’. Landscape and urban planning, 125, 234-244.

Further resources: