The City of Cape Town’s Recreation and Parks Department recently completed a tree mapping project – the first of its kind in South Africa.
The Tree Canopy Mapping Project
According to a recent press release, the pilot project started in June last year and will provide extensive data on all trees within the city.
“While the City has a tree management policy which ensures that trees are cared for through proper arboriculture techniques and management practices, mapping our trees will further assist us in decision making on where to focus tree planting efforts, especially if overlaid with heat island maps,” said the Mayoral Committee Member for Community Services and Health, Councilor Zahid Badroodien. “Implementing techniques such as selection, planting, training, fertilisation, pest control and pruning are important in caring for our trees. Trees play an important interface role between the environment and the urban landscape.”
The Food and Agriculture Organisation of the United Nations defines an urban forest as “a contiguous area with over 10% tree canopy cover”. The City of Cape Town’s tree canopy cover currently stands at 7%. So, to limit the extent of the data, trees captured as part of the study only included trees of 2.75 meters and higher.
An important component of managing the Urban Forest is a tree inventory. The data record for a tree typically includes information about tree species, location, characteristics, images, maintenance history, risk assessment and further maintenance and management needs.
Tree canopy mapping integrates cutting edge automated feature extraction with detailed manual quality assurance in GIS (Geographic Information System). Tree canopy extraction is reliant on remotely sensed data in the form of infra-red images and light detection and ranging (LiDAR) data. The City acquired a 2018 colour infra-red image and this enabled the tree canopies to be distinguished by their colour properties. LiDAR (or 3D height information) data was then used to enhance the accuracy of the information by excluding low-lying vegetation and shrubs from the output.
This pilot project reportedly provides a learning opportunity and skill transfer between various departments and the information extracted will also benefit other municipal services such as spatial planning, and environmental management.
Analysis from the tree canopy dataset could also determine the average height of trees and categorise the percentage of trees within a certain height bracket. Further to the above, the Tree Canopy Mapping Project also allows for retrieving additional information which includes;
- Area of vegetation (road reserves, parks, private land)
- Leafy versus non-leafy areas suburbs for planning purpose
- Percentage of tree canopy baseline to compare to future surveys and monitor canopy cover changes
- Estimated height of trees
“The value of trees cannot be overestimated. While they assist in providing cleaner air, they also offer environmental protection against erosion and acting as noise buffers. Let us all care for our trees so that future generations also have access to beautiful parks and open spaces,” Badroodien added.