Healthy Places, Healthy People Shade tree guidance

Shade provides numerous health benefits and can help protect communities from the harmful effects of excessive ultraviolet (UV) radiation exposure and future skin cancer risk. Tree canopy plays a fundamental role in its natural contribution to shade within our urban environments.

There is a limited evidence-base for tree planting that focuses on reducing UV radiation exposure and advice for practitioners to optimise shade tree provision in the built environment.

Queensland Health has commissioned academic research with Professor Nathan Downs of University of Southern Queensland (USQ) to identify optimal tree species to maximise UV radiation protection and shade provision. CanopyCast has been developed to translate technical evidence-based data generated by Professor Nathan Downs into a practical application. It will analyse UV radiation and shade protection for various tree forms and densities and along footpaths positioned in various orientations.

CanopyCast is a digital solar analysis application that analyses shade and UV index reduction provided by trees. It has been developed to help inform decision makers and local governments in the planning and planting of shade trees.

The Shade tree guidance presents the research and thinking that has informed CanopyCast and summarises relevant advice for the delivery of shade tree planning and planting within Queensland.

Queensland Health engaged government, local government and organisations who have responsibility for specific built and natural environment policy, planning, investment directions and delivery throughout the process. The stakeholders and a broad understanding of industry processes and literature have informed and shaped CanopyCast and Shade tree guidance.

CanopyCast is a digital solar analysis application that analyses shade and UV index reduction provided by trees. It has been developed to help inform decision makers and local governments in the planning and planting of shade trees along footpaths.

UV radiation is a complex concept that has been translated into CanopyCast to represent how trees can protect humans from harmful sun exposure. CanopyCast expands on the concept and research of UV radiation to translate it into practical guidance and an application that can be implemented by the built environment industry. The following section explains the research on UV radiation and how it was calculated for use in CanopyCast.

Explore CanopyCast:

The sun emits many types of radiation, including visible radiation which the earth receives as light, infrared radiation which is received as heat, and UV radiation which is not visible or can be felt. Overexposure to UV radiation can cause sunburn, skin damage and skin cancer. This radiation is measured by an international standard called the ultraviolet index, or UV index, which indicates the strength of UV radiation from the sun on the ground. This index is calculated based on the skin’s response to UV radiation, in order to give an indication of its harm to humans at any particular time.

A UV index of 1-2 is low, which generally means it's safe to be outdoors unprotected. However, advice from The World Health Organisation and the Cancer Council is to protect the skin from the sun when the UV index is 3 or higher.

Understanding how this UV index can be reduced by either natural or built shade is an important factor in protecting humans from the health effects of UV radiation exposure. As a central source of shade in the environment, it was important for CanopyCast to assess how trees can protect against UV radiation. Published in the Applied Geography journal in 2019, research from the paper,  “Comparing the annualised dynamic shade characteristics of twenty-one tree canopies across twenty-six municipalities in a high ambient UV climate, Queensland – Australia”  by Professor Nathan Downs was used to determine the UV index reduction by tree shade [5].

In this paper, Professor Downs identifies the ‘sky fraction’ value of 21 different tree species. A sky fraction value indicates the percentage of the sky that is visible when viewing from the underside of tree canopies. The unique sky fraction values give a representation of the trees’ canopy density, allowing for the interpretation of how much UV radiation from the sun perforates through the trees’ canopies.

The sky fraction value of six tree forms derived from Professor Down’s paper were selected for use in CanopyCast based on their environmental characteristics. The sky fraction values were incorporated into a calculation specified by Professor Downs to determine the unique UV index value that each tree produces in the areas where shade was cast. This calculation uses UV index data obtained from the Australian Government ARPANSA website, which provides live and unobstructed UV index data which is collected by detectors that respond to UV radiation in a manner similar to human skin [1].

These data sources combined provide the means to represent UV index level reduction via tree shade in CanopyCast.

A number of factors inform CanopyCast which relate to tree form or placement. The factors are:

• Form and spacing
• Time
• Orientation

CanopyCast demonstrates a percentage of UV protection by calculating the area of footpath that receives any amount of shade cast by trees within the selected 3-hour timeframes.

Tree planting on both sides of the path is the ideal outcome for maximum shade in any context and orientation. Consequently, the key messages do not report on this scenario and only consider either side of the path for optimised design recommendations.

The following key messages show the optimised UV protection and shade across a variety of different scenarios: 

Optimising UV protection should consider the users and time of day; however, analysis shows that each footpath orientation tested provides the optimum shade (between the hours of 8-5pm) when trees are planted to the following sides of path:

Analysis shows that within the three timeframes the following tree forms provide the optimum shade across all footpath orientations and all sides of the path tested:

Analysis shows that for each footpath orientation tested, planting on the following sides of the path provide the optimum shade for each timeframe:

Five locations across Queensland have been selected based on the following:

• Geographical location – to provide a range of climate conditions and sun position results.
• Functions – to test places that could be identified as priority planting areas to serve greatest user need for shade and UV protection.
• Context – to assist the understanding of how to apply CanopyCast to different design projects.

The locations explored in CanopyCast have not considered design aspects such as above and below ground utilities, road reserve setbacks and clearances, access requirements etc. The  Resources  section provides direction on when and how the recommended guidance can assist decision-making and overcoming of these design constraints.

The map shows the locations and explanation for each selection.

Analysis has informed the following recommendations that could be applied to the design thinking for varying contexts and user needs identified in the five locations above:

Explore more:

[1]         arpansa. (2023). Sun exposure and health. (Australian Government) Retrieved from arpansa: https://www.arpansa.gov.au/understanding-radiation/radiation-sources/more-radiation-sources/sun-exposure

[2]         Astell-Burt, T., & Feng, X. (2019). Association of Urban Green Space With Mental Health and General Health Among Adults in Australia. JAMA Network Open.

[3]         Christian, H., Lester, L., Trost, S., Trapp, G., Schipperijn, J., Boruff, B., . . . Eslick, H. (2019). Shade coverage, ultraviolet radiation and children's physical activity in early childhood education and care. International Journal of Public Health, 1325-1333.

[4]         Diabetes Australia. (2022, April 5). AIHW data shows diabetes costs the health system almost $2.5B per annum. Retrieved June 29, 2023

[5]         Downs, N., Baldwin, L., Parisi, A., Butler, H., Vanos, J., Beckman, M., & Harrison, S. (2019). Comparing the annualised dynamic shade characteristics of twenty-one tree canopies across twenty-six municipalities in a high ambient UV climate, Queensland - Australia. Applied Geography, 74-82.

[6]         James, P., Banay, R., Hart, J., & Laden, F. (2015). A Review of the Health Benefits of Greenness. Curr Epidemiol Rep, 131-142.

[7]         Jones, B. (2019). Tree Shade, Temperature, and Human Health: Evidence from Invasive Species-induced Deforestation. Ecological Economics, 156, 12-23.

[8]         Langenheim, N., White, M., Tapper, N., Livesley, S., & Ramirez-Lovering, D. (2020). Right tree, right place, right time: A visual-functional design approach to select and place trees for optimal shade benefit to commuting pedestrians. Sustainable Cities and Society, 52, 101816.

[9]         Lovasi, G. S., Quinn, J. W., Neckermann, K. M., Perzanowski, M. S., & Rundle, A. (2008). Children living in areas with more street trees have lower prevalence of asthma. Journal of Epidemiology & Community Health, 62, 647-649.

[10]      Parisi, A., Kimlin, M., Wong, J., & Wilson, M. (2001). Solar ultraviolet exposures at ground level in tree shade during summer in south east Queensland. International Journal of Environmental Health Research, 117-27.

[11]      Parsons, P., Neale, R., Wolski, P., & Green, A. (1998). The shady side of solar protection. The Medical Journal of Australia, 327–330.

[12]      Ulmer, J., Wolf, K., Backman, D., Tretheway, R., Blain, C., O'Neil-Dunne, J., & Frank, L. (2016). Multiple health benefits of urban tree canopy: The mounting evidence for a green prescription. Health Place, 54-62.

[13]      UN. (2018, March 21). As cities boom, forests key to meeting demands for water, food and energy – UN. Retrieved from UN News: https://news.un.org/en/story/2018/03/1005561

[14]      WWF, Australia and Doctors for the Environment Australia. (2023). Trees: The forgotten heroes for our health. Carlton: WWF/DEA.

Suggested workflows for mapping tree canopy and calculating canopy coverage are listed below in a sliding scale of user-friendliness, complexity and accuracy. When selecting suitable method, it is important to consider not only scale, but also cost, experience, accessibility, along with user ability and knowledge and the level of accuracy required.

Each method is identified to simply calculate canopy coverage. All methods use the same methodology to calculate percentage canopy coverage, but differ in how the canopy data is collected.

For all methods the percentage cover is calculated using equation 1, where Pc is percentage cover, Mc is Measured Canopy and AOI is measured Area of Interest.

GIS Platforms – Manual Canopy Creation Google Earth Pro/QGIS/ArcGIS

Google Earth Pro, QGIS and ArcGIS are geospatial desktop applications that allow users to view relatively high-resolution aerial imagery. For smaller areas such as streets in urban areas, these platforms can be used to manually trace over geo-referenced imagery to create a polygon feature class around the desired tree canopy extents. A polygon feature class contains vector imagery of a feature and its attributes. The calculated areas of canopy and polygon of the area of interest can be used to obtain the percentage cover. This is undertaken by clipping out the geometry that falls within the area of interest and using that as the measured canopy area.

This method is relatively easy for small areas and inexpensive if using QGIS or Google Earth Pro, both of which are free software. However, this method could be onerous for larger areas and present challenge to determine a tree and a shrub from a flat image. This difficulty could result in a low level of accuracy from the analysis.

iTree Canopy

Developed by the United States Department of Agriculture, iTree Canopy is an open access tool available on a web browser. This tool can be used to determine the amount of an interest area covered by tree canopy. It photo-interprets tree canopy and other land cover classes using Google Maps imagery and by randomly selecting points across a study area then estimates tree canopy coverage. This tool can be used to generate assumptions on tree canopy coverage by following steps:

• Select a boundary by either selecting from existing geographic boundaries or manually uploading a project boundary. Multiple boundaries that do not overlap may be used at the same time.
• The tool will generate random sample points within these boundaries and allows users to assign each point a cover type from a pre-defined list. The more locations that the user categorises, the more accurate the analysis.
• The tool then calculates an indicative tree canopy coverage result for the identified area, as well as an estimate of tree benefits.

LiDAR

Light Detection and Ranging (LiDAR) data is collected from aircraft or drones using sensors that detect reflections of a pulsed laser beam to sample the surface of the earth, producing highly accurate 3D elevation points. LiDAR data produces point-cloud datasets that can be managed, viewed and analysed in GIS software or dedicated point cloud software. These point-cloud datasets can be requested for download from  ELVIS , a free, open source resource from the Intergovernmental Committee on Surveying and Mapping government agency. In Queensland, there is LiDAR data available on ELVIS along the east coast, major cities and at select townships throughout the state. The vegetation points that are included in LiDAR datasets are classified as low, medium and high vegetation. By using these classifications, LiDAR datasets can be used to generate assumptions on tree canopy coverage and canopy heights through the following steps:

• Download the relevant LiDAR datasets from ELVIS.
• Clean, re-classify and remove any inaccurate or erroneous data in a geospatial transformation software platform such as Feature Manipulation Engine (FME). Some datasets have been classified to a lesser extent than others which is dependent on the year of flight and methods used for cleanup. Datasets often have overhead powerlines and some tall buildings classified as high vegetation. It is recommended to visually audit data to understand what additional cleaning operations need to be considered as part of this workflow.
• Use FME to generate raster or a polygon feature class of the tree canopy form the cleaned vegetation points with associated height data embedded. Raster data is ‘lighter’ and faster to process.
• Create a polygon boundary for the analysis area.
• Canopy cover percentages can then be calculated using the analysis boundary and the vegetation points identified in the LiDAR data to indicate tree canopy coverage.

Machine Learning

• With advances in artificial intelligence (AI) and availability of training datasets, machine learning is fast becoming a reliable method for mapping tree canopy in urban areas and can be scaled to very large areas.
• This method works best on very high-resolution aerial imagery and can extract pixel level tree canopy.
• Once a canopy dataset has been generated, an area of interest polygon is created and the percentage of cover is calculated.

In all the methods listed above it has been assumed that the area of interest is a manually created polygon. However, the canopy cover dataset is a geo-referenced dataset therefore it is possible to run percentage coverage analysis against any polygon data, such as land use, active transport infrastructure, suburbs and even a Council Local Government Area (LGA). Data is readily available from most if not all LGA’s for extensive downstream analysis to be performed.

A tree canopy target refers to the percentage that indicates the increase the coverage and extent of tree canopies within a particular area. Setting a target for tree canopy involves determining the desired percentage or amount of tree cover within a specific area. Here are some steps to help you set a target for tree canopy: 

• Define your drivers: Identify the specific drivers you want to achieve through increasing tree canopy. These objectives could include increasing walkability improving air quality, providing recreational spaces. Having clear drivers will help in setting a meaningful target. 
• Understand your assets and opportunities: 
  • Define the geographic scope: Determine the specific area for which a tree canopy target needs to be set. This could be the whole of an LGA, suburbs or a  priority planting area .   
  • Assess the current tree canopy coverage: Conduct an assessment of the existing tree canopy coverage within the defined area ( Tree canopy mapping processes  discusses different methods to deliver this). Analyse the data to determine the current tree cover percentage.
  • Research and benchmark: Look for benchmarks and best practices from similar regions or organisations. Research tree canopy targets that have been set in comparable locations to get an idea of realistic goals. Open sources of tree canopy cover target case studies are discussed  here .
• Governance, policy and guidance:  
  • Engage stakeholders: Involve relevant stakeholders such as local government members, urban planners, environmental organisations, and community members. It is critical to seek their input and support throughout the target-setting process to agree, commit and deliver.  
• Set shade and health priorities:  
  • Agree shade tree goals and targets: Based on the baseline information gathered and the drivers defined, set a target for the desired tree canopy coverage. This target can be expressed as a percentage of tree cover for the entire area or as a specific number of trees to be planted and should be reflective of actual space and ability to plant and deliver trees on the ground.  
  • Agree shade tree objectives: Create an action plan outlining the strategies and steps needed to achieve the tree canopy target. This may include initiatives like tree planting programs, tree preservation policies, urban forestry management plans, community engagement campaigns, and partnerships with relevant organisations. 
  • Community stewardship and advocacy: Celebrate achievements and communicate the positive impact of increasing tree canopy to stakeholders, decision-makers, and the community at large. This will help build support and momentum.
• Deliver: 
  • Champion pilot projects: Advocate for small-scale planting projects that tests and demonstrates the benefits of the tree planting action plan. The outcomes and lessons learned from the pilot project may provide opportunity for supporting future funding and expanding the strategy to a larger scale. 
  • Monitor and evaluate progress: Regularly monitor and evaluate the progress towards the tree canopy target.  Tree canopy mapping processes  discusses different methods to do this. Adjust the action plan as needed to address challenges and ensure steady and attainable progress.

City of Sydney: Greening Sydney Strategy “Our target is to increase our overall green cover to 40 per cent across the local area, including a minimum of 27 per cent tree canopy by 2050.”  Link here 

Brisbane City Council: Clean and Green Brisbane - Urban Forests “Future goals and targets to enhance and sustain our urban forest are to:

• increase tree shade cover to 50% for footpaths and bikeways in residential areas by 2031
• increase shade at bus stops
• transform major entry roads to the city into subtropical boulevards.”

 Link here 

Sunshine Coast Regional Council: Planning Scheme Policy

The Sunshine Coast Planning Scheme, Landscape Code Acceptable Outcome AO28.1 asks development to achieve 80% shade at maturity for landscapes that incorporate protective shade to public and communal spaces.

 Link here 

Moreton Bay Regional Council: Going Green as We Grow Siting commitments such as “Tree plantings will increase 30 per cent” with “210,000 trees to be planted at strategic locations”.

 Link here 

City of Ipswich: Urban Greening - Putting the Plan into Action 2022 “Focus area 1, Green the urban footprint of Ipswich – Target: Increase canopy cover in high priority suburbs by a minimum of 10% by 2042.”

 Link here 

Mackay Regional Council: Urban Greening Strategy

“By 2042, Mackay Council aim to achieve: an average of 40% tree canopy cover over pathways (up from 16.8% in 2021) an average of 40% tree canopy cover over public parks and the open space network (up from 33.6% in 2021); and an annual net gain of public tree numbers ensuring more trees are planted than removed.”

 Link here 

The process outlined in  Evidence to Action  will help deliver on an organisation, local government or regional council’s specific priorities. As evident in  Resources , the following are considered to be priority planting areas that maximise health benefits and return on investment:

Active Transport Networks

Active transport networks, such as pedestrian and cycling routes, are heavily utilised by people for commuting, exercise, and recreational purposes. AT pathways is an asset that is often prioritised for investment and upgrade through differing funding avenues (list a few – State Infra Plan, in conjunction with road upgrades etc) and is a crucial way to create shade and reduce UV impact.  

Community destination catchments

Planting trees in the catchments of highly trafficked community destinations such as educational institutions will provide for improved shade which encourage the use of active transport to access these destinations and assist in reduction of UV exposure. Coupling tree canopy increase with community facilities such as the following also provides opportunity for co-funding of delivery of trees: 

• Shopping precincts and high streets 
• Health precincts  
• Transport hubs  
• Education facilities  

Recreation areas

Parks, recreational areas, and other public spaces are often Council owned land. They are spaces that are often frequented by volumes of people that can benefit from increased tree cover to provide shade for health and well-being benefits including reduction of UV exposure.

Local streets and neighbourhoods  

The road reserve is often Council or publicly owned land. They are networks that are heavily utilised by pedestrians and cyclists to travel between destinations or for recreation purposes. Streets and road infrastructure are assets that are often prioritised for investment and upgrade. Co-delivering new shade tree plantings with these projects is an important mechanism to increase tree canopy to support healthy, walkable neighbourhoods.  

Generally, an organisation, local government or regional council will assess and provide targets on land within their jurisdiction. This is because it is within their control and managed by them, allowing them to implement long-term planning strategies.