The Delta Park Centre surrounded by indigenous plants and trees

ECOLOGICAL purists would argue that all 'exotics', or alien trees or plants, should be removed from Johannesburg's public spaces - but the evidence proves that exotics do have a role to play.

Delta Park, some 10 kilometres north-west of the city centre, is a 104-hectare green lung, mostly planted with exotics. "Delta Environmental Centre is living proof that exotics can co-exist happily with indigenous vegetation," says Geoff Lockwood, ornithologist, resident manager and education officer at Delta Park. In fact, if all the exotics were removed from the Bird Sanctuary at the park, there would only be about eight trees left, says Lockwood.

Since its inception in 1886, Johannesburg has been actively planted with exotics like oaks and planes, which still line many of the city's suburban streets, making the suburbs look like an urban forest. These exotics are better suited to pavement planting than indigenous trees, which have thorns that can hurt passers-by and root systems that interfere with drainage. They are also not easily pruned.

There was a period in Delta Park's history when it was believed that indigenous trees would not grow in the veld. So in 1941 a plantation of poplars was started in the park. They have highly invasive root systems, and are very thirsty trees.

But on the other hand, the exotics have created a dense and lush habitat for birds, which will eat whatever fruit or seed the exotics produce.

"The Chinese Elm provides seeds for doves, and the eucalyptus trees attract bees, which attract the bee-eating birds. Chinese Privet bushes produce purple berries which the Rameron Pigeons eat," says Di Beeton, executive officer at the Park.

Delta Park and surrounding suburbs in 1934 when it was laid out. The area below the road is now a woodland attracting many birds

Delta Park and surrounding suburbs in 1934 when it was laid out. The area below the road is now a woodland attracting many birds.

In the last two decades numerous indigenous trees and shrubs have been planted, particularly around the Delta building.

Delta Park was established in 1934 as a waste water treatment plant, at the time one of the most advanced treatment plants in the world. But as Johannesburg grew, its capacity became too small for the city, and in 1963 the plant was moved to Diepsloot. The main building was constructed during a period when Johannesburg was experiencing a rush of Art Deco construction, and it has a simple elegance in its Art Deco style.

After the plant was relocated, the building and surrounding open spaces became run down and overgrown, and in 1975 the municipality planned to demolish the building. The founder of Delta Park, Norman Bloom, persuaded the city authorities to lease the building to him at a nominal rental. A Section 21 company was registered and the SA Nature Conservation Centre came into being. In 1992 it changed its name to the Delta Environmental Centre.