|Image: Urban tree canopy, Johannesburg, photo by Dorothy Tang|
Beginning in the early 1900s, the city of Johannesburg introduced large shade trees to alleviate airborne dust from the mining belt. Originally a semi-arid grassland ecosystem, Johannesburg now boasts the largest urban canopy in the world. Most trees are alien species from other parts of the world, such as Jacaranda, Eucalyptus and English Oak, and many require large quantities of water for irrigation, an added burden to a region with limited water resources.
|Image: Eucalyptus grove, Johannesburg, photo by Dorothy Tang|
The native Australian tree Eucalyptus was introduced by Australian gold miners to provide strong timber support for deep shaft mining and related construction. In addition, its high evapotranspiration rate encouraged mining companies to plant it near the foot of mine dumps to capture excess contaminated run-off. Today eucalyptus presents a hazard in informal settlements because of its short life span; the falling limbs and trunks of overgrown mature trees are a hazard in communities that do not have the means to manage their growth.