Leafy cover from tree canopy provides environmental, social, psychological and recreational benefits in our cities and towns. This environmental asset, known collectively as ‘urban forest’, includes all trees on public and private land.
The importance of urban forest in developed areas is prompting State and local governments to take steps to improve and manage tree canopy, using scientific forest management principles.
In the Perth and Peel regions, a number of local governments have already developed plans to enhance tree canopy within their boundaries.
The Western Australian Planning Commission’s (WAPC) Better Urban Forest Planning guide and Urban Tree Canopy Dashboard are designed to assist these and other urban forest managers, with best practice actions and data to support the ongoing management of their urban forests.
Better Urban Forest Planning, developed in association with WALGA, is a guide that helps local government and the community plan and manage urban forests for current and future generations.
Since 2009, the WAPC, through the Department of Planning, Lands and Heritage, has been working with the Commonwealth Scientific Investigation and Research Organisation (CSIRO) to create urban tree canopy mapping data drawn from high resolution aerial imagery of the metropolitan region.
This data can be used with local government planning and environmental data to further benefit local urban forest management strategies.
Urban forest mapping data can be downloaded by local government area from Landgate as detailed GIS shape files, and is available on PlanWA for general viewing.
The Western Australian Planning Commission’s Urban Tree Canopy Dashboard is an interactive snapshot of the extent of tree canopy coverage across the Perth and Peel regions.
Urban tree canopy mapping data for 2014, 2016 and 2018 has been used to create the dashboard, which offers an accessible and consistent monitoring and reporting function.
The dashboard uses spatial data gathered from high resolution aerial imagery through the CSIRO’s Urban Monitor program and analysed by the Department of Planning, Lands and Heritage, to measure and monitor tree canopy trends across Perth and Peel. Local governments can use the data to track their tree canopies over time.
The dashboard shows the growth, loss or change of urban canopy, in any given area, over time. It provides key statistics and trends for all suburbs within Perth and Peel. Information is available on either a suburb or local government area level, and is categorised into Street blocks (combined lots), Roads, and Parks.
Canopy data is presented at three height levels and by total canopy coverage above three metres. Further data is shown by land ownership and local planning scheme zones, and can indicate changes and trends across suburbs.
To ensure consistent annual data comparisons, the same lot boundaries are used each year, regardless of any boundary changes.
The dashboard is not intended as a comparison tool between suburbs or local governments as each area is subject to different conditions and land use purposes.
Guidance notes for using the urban tree canopy dashboard.
Spatial extent: Perth and Peel regions, Western Australia
Description: Using the CSIRO’s Urban Monitor high resolution digital imagery, vegetation height strata of endemic and exotic species has been calculated and reported as an area for each height strata of 0–3 metres, 3–8 metres, 8–15 metres and 15+ metres.
The area of grass-covered areas falling into the 0–50 centimetre range has also been calculated and recorded in square metres and percentage of total parcel area.
Vegetation coverage greater than three metres in height has been deemed tree canopy. The canopies have been aggregated and reported as total canopy coverage in square metres, percentage of total parcel area and percentage range.
Note: As is common in big data, some anomalies may occur. Some areas may have incomplete coverage or are excluded from Urban Forest in some years.
Who can access the data?Show more
The urban tree canopy data is available on the Department of Planning, Lands and Heritage website. State and local government agencies can access related data shape files through Landgate’s SLIP system (DataWA).
What is the data used for?Show more
Local governments can use the data to track and plan their tree canopies over time.
Where does the data come from?Show more
The CSIRO sources the data for the Western Australian Planning Commission from high resolution (0.2 metre cell size) aerial digital images of the Perth and Peel regions. It is collated through the CSIRO's Urban Monitor program before being transferred to Geographic Information System (GIS) data files, for analysis by the Department of Planning, Lands and Heritage.
How often is the data captured and updated?Show more
The aerial images are captured in late January each year. The tree canopy data is captured, processed and updated every second year.
What is included in the street blocks, parks and roads categories?Show more
Most of the tree canopy data falls under three broad land use categories that include specific land use zonings:
- ‘Street blocks’ – includes a combination of lots zoned for residential, commercial, industrial, hospital/medical, educational, and some agricultural and transport uses
- ‘Roads’ – includes the reserved verges of roads and streets managed by local or state governments
- ‘Parks’ – includes public parks, open space, private recreation/sporting grounds and State forest.
Some land use categories are too complex to include in the dashboard but can be found in the tree canopy metadata.
What are the error margins in the data?Show more
Data percentages are rounded to the nearest whole number. The data error margin is believed to be very minimal and most likely due to expected variances between technologies and methods of capture.
Are there gaps in the data?Show more
Large complex data sets can have data gaps or occasional anomalies due to human error or technical glitches, such as small areas not being captured properly in aerial imagery. Measures are in place to eliminate or identify errors in the tree canopy data. Any detected anomalies in the published data can be reported to SpatialAnalyst@dplh.wa.gov.au.
Will more density and development reduce tree canopy?Show more
Tree canopy in parks and on road reserves is less likely to be affected by development. It is also easily improved in areas with underground power and tree planting programs in place.
Trees on street blocks (lots) may be affected depending on the design of a development and approval requirements. Under the State Government’s DesignWA policy, future precincts are required to have more detailed considerations for trees on public land, including deep soil areas to support new tree canopy in medium and high density development.
Why are the rates of growth between land use categories different?Show more
Canopy growth rates can differ within the land use categories. For example, data can change rapidly when trees on road verges are trimmed, while land owner decisions can affect trees on street blocks.
Among the land use categories, canopy growth rates are found to be highest in parks and streets with underground power; and local governments with active tree planting regimes show up in data trends over time.
What factors contribute to simultaneous canopy loss and gain?Show more
Tree canopy changes constantly. Factors that influence canopy loss and gain may include particular land use activities occurring at the point of data capture. For example, subdivision, street tree trimming, climate conditions (high rainfall years can affect canopy growth), fires in bush reserves, development policy settings or implementation of a tree planning program.
Tree canopy can also increase even where trees have been lost because the retained trees will continue to grow.