The Gauteng Smallholder has written extensively over the years about the challenges we face in dealing with invasive alien plants (IAPs). When it comes to trees on our plots, now is a good time to cut down exotic trees or remove dead trees and to replace them with a suitable indigenous tree.

Our focus would be on eliminating invasive aliens, which are a threat to our natural biodiversity. What makes an alien plant become an invader?

  • Absence of natural enemies.
  • Similar conditions to native country.
  • Vegetative reproduction.
  • Prolific seed production, long-lived seeds.
  • Effective seed dispersal mechanisms, such as water, wind and birds.

However, just because a tree is indigenous doesn’t mean that it will grow well on a Gauteng plot. Trees from the Western Cape with its wet winters or from some areas in Kwa Zulu Natal will find our frosty winters too hard to handle.

A common alien tree that should be replaced is Acacia Mearnsii or Black Wattle. This tree competes with and replaces indigenous grassland and riverine species. Your plot can be invaded by dense thickets of black wattle, which reduces the grazing area for your livestock. An evergreen tree growing 5-10m high, black wattle has dark olive-green, finely hairy leaves, rough, greyish bark, small pale yellow to cream, globe-shaped flowers in large, fragrant sprays, (August to September) and finely haired, dark brown seed pods.

Rhus lancea

If you are replacing the tree in your garden, you will want something of a similar size and shape.

You might consider one of the species of Karee as a replacement.

Rhus lancea Karee is a very hardy, evergreen, drought resistant tree with a graceful, weeping form. The dark, fissured bark contrasts beautifully with the long, thin, bright, trifoliate leaves.

The inconspicuous yellow-green flowers (male and female flowers on separate plants, therefore only female plants bear fruit) from June to September attract insects and are followed by bunches of edible fruit that attract birds. The small flowers are borne in abundance and give the tree a lacy look when in bloom.

It thrives in clay soils and is fast growing if watered regularly, even though it is also drought hardy. It makes a great climbing tree for children if the lower branches are not pruned off.

Plant in sun or semi-shade in virtually any soil type and it grows up to 8m.

Rhus leptodictya, Mountain Karee, is also  very hardy, evergreen, drought resistant, small, decorative tree with a drooping crown of bright green foliage. The bark on young stems is reddish brown, becoming darker and rougher as the tree matures. The lovely reddish wood is used to make beautiful small pieces of furniture.

The inconspicuous flowers are borne from January to April. These are followed by bunches of edible fruit which attract birds to the garden.

It grows in most soil types and makes a beautiful, graceful tree that is ideal for a small garden in sun or semi-shade. It is also beautiful as a small avenue tree.

A valuable fodder tree especially in times of drought or when little else palatable is green in the veld.

The tree should also not be too slow growing. Of course the terms ‘fast’ and ‘slow’ in the context of trees are relative terms. Indigenous highveld trees usually grow at a rate of between half a metre to a metre in a year – patience is always required when growing trees.

The Buddleja saligna, False Olive, has become one of the most popular indigenous trees in Gauteng, due partly to its relatively fast growth. It can reach a height of 3 – 4 metres in just a few years, thus providing excellent screening in the shortest possible time. However, being fast does have its disadvantages. Sometimes the Buddleja can look ‘scruffy’ after a few years, and because the branches are not as strong as other species, they often tend to droop after heavy rains, especially if they are carrying masses of flowers. Despite these potential drawbacks this is still a worthwhile species to choose. If you allow it to grow into its natural form, you will be rewarded with masses of white flowers which attract a multitude of insects, and it’s not uncommon to see this plant covered in beetles, ants, butterflies and bees during the flowering season.

2 thoughts on “Replacing Exotic Trees

  1. A first class article ,however just like animals,we humans cannot live on just indigenous crops,imagine our meals without potatoes, peppers,onions,beans ,peas or butternut Etc…animals get almost zero feed from for instance sweet thorn,or fever trees,compared with Lueceana,mulberry or tree lucerne.

    1. The subject of “alien” invasive plants , I think, is not treated much deeper. For example, we seldom look at various factors that influence plant species invasion. Globalisation and international trade has almost obliterated the barriers that separated peoples and nations of the world. Therefore, the spread and wide distribution of these “weedy” plant species is a reflection of human behaviour. International trade in plant species allows them to overcome their natural range and to establish in new habitats elsewhere in the world. Also seeds may be spread via transportation. One of the most profound factors promoting the proliferation of alien plant species is rapid urbanisation. The urban areas have many modified patches of lands where habitats previously occupied by native vegetation are now novel habitats characterised by impervious surfaces, compacted soils, built infrastructure, environmental pollution and unusually high temperature levels. These seemingly inhospitable ecosystems are taken over by these alien invasive species because of their pre-adaptation to such habitats. On the other hand, local native plant species are excluded from these disturbed environments. Therefore, it would be prudent to look at how we use the land and try to avoid creating disturbed conditions that may favour alien plant species. Have we noticed how abandoned buildings and waste dumps accommodate various plant species. Some of the trees are Tecoma stans, Melia azedarach, Ricinus communis, Solanum mauritianum to add but a few species that are now prevalent in Gauteng.

Leave a Reply

Your email address will not be published. Required fields are marked *