An image from the City of Cape Town’s Tree Canopy Mapping project.
Rolling out Cape Town’s Tree Canopy Management Project to other cities and towns could be a valuable tool in coordinating urban tree-planting initiatives under the government’s Plant a Million Trees Campaign and managing risks at the wildfire-urban interface.
The City of Cape Town completed South Africa’s first-ever tree mapping exercise two years ago and found that its tree canopy cover is 7%. The data is for trees that are 2,75m and higher. The United Nations Food and Agriculture Organisation (FAO) defines an urban forest as “a contiguous area with over 10% tree canopy cover”.
The Tree Canopy Management Project provides Cape Town with an inventory of trees. The data record for a tree includes information about the species, location, characteristics, images, maintenance history, risk assessment and further maintenance and management needs.
Spatial planning
The project facilitates communication between municipal departments involved in spatial planning and environmental management. It assists in deciding where to focus tree planting efforts, especially when overlaid with heat island maps.
Tree canopy mapping relies on remotely sensed data in the form of infra-red images and light detection and ranging (LiDAR) data. The mapping integrates cutting-edge automated feature extraction with quality assurance within a geographic information system (GIS).
The city used a colour infra-red image that distinguishes tree canopies by their colour properties. LiDAR provided 3D height information that enhanced the accuracy of the data by excluding low-lying vegetation and shrubs.
Data-driven decisions
Analysis of a tree canopy dataset determines the average height of trees and categorises the percentage of trees within a certain height bracket. The information includes:
- Areas of vegetation along road reserves and in parks and private land
- Leafy versus non-leafy areas in the suburbs for planning purposes
- Percentage of tree canopy baseline to compare with future surveys to monitor canopy cover changes
- The estimated height of trees 2,75m and higher
The city says its management programmes include skills development, site identification, tree selection, planting, fertilisation, pest control and pruning.
Best Practice Guidelines for Trees
In 2020 Cape Town brought out a book on Trees: Best Practice Guidelines.
It provides guidelines for property owners, architects, planners, and community members to manage and improve green infrastructure collectively. It emphasises the need for tree planting plans to be specific to the various micro-climates created by the Table Mountain chain.
Careful planning based on scientific research and plant selection based on context will assist in preventing adverse impacts on biodiversity and encourage climate-adaptive cities and towns.
