Chris Dalzell
Durban - I have just returned from an epic six-day hike on the Amathola trail in the Eastern Cape where I experienced some of South Africa’s most pristine indigenous forests and found plants I have been searching for since 1990.
The forests once covered vast tracts of South Africa but, over the past 150 years, have been removed to plant timber forests and create space for farming. Walking from an indigenous forest that displayed such a variety of plants into a wattle plantation that was devoid of any other plants was shocking.
Trees, such as wattle and pine, are planted for the timber industry and grow quickly, but what they do to our grasslands and once-indigenous forests is a huge concern for the future of the once magnificent forests. The exotic trees spread seed throughout the indigenous forests which grow quickly and kill future growth of our indigenous trees.
When I was a young student in the mid ’80s, exotic plants were used mostly in the landscape industry. Slowly, through the influence of several individuals and organisations such as the Botanical Society of South Africa, the indigenous gardening craze took off and today, most nurseries house a huge variety of local indigenous plants. Walking through the indigenous forests of Amathola was like walking through the garden of Eden.
Sadly, when you take a closer look at what is found along roadsides and freeways of eThekwini you will understand why we need to remove these plants and encourage the local grasses and wildflowers to dominate the landscape.
Alien weeds do not have natural predators to prevent the spread of the seeds and once they flower and go to seed, these are then spread either by wind or insects. They then germinate, producing plants that grow quickly and before long, the cycle starts again and you have a huge problem.
One of the main reasons many gardens are full of alien plants is lack of knowledge. This article will look at some of the most invasive plants in our area, how to remove them and what to plant in their place.
Alien plants are any plant that does not occur naturally within a region, grows rapidly, and colonises water sources and land.
Why are they bad?
- They seed and spread rapidly at the expense of our natural flora thus reducing species diversity.
- pH is altered and makes rehabilitation of areas difficult after the removal of alien plants.
- Many alien plants do not decompose quickly, resulting in leaching of nutrients, erosion and degradation of the topsoil.
- The removal of ground water is seen especially in wattle plantations. Recent removal of wattle in Babanango Game Reserve has resulted in rivers flowing for the first time in 30 years.
- Fires are more prevalent due to the increase in the fuel load which results in “hot burns”. Cape Town experiences such fires in summer.
- There is an increase in erosion as many of the alien plants do not have a root system that binds the soil, resulting in flooding during heavy rains.
Legally, under regulation 15 of the Conservation of Agricultural Resources Act 1983, it is the responsibility of the landowner to keep their land free of invasive alien plants. This means when you buy or sell a property you need to make sure it is free of alien invasive plants.
Clearing aliens can be expensive. You can manage these trees by removing seedlings that germinate and, when funds are available, remove them. If you have trees that provide privacy, inter-plant with a quick-growing indigenous tree and when it’s of a size to provide privacy, remove the alien tree.
Most nurseries are audited so should not sell plants that are on the alien list.
When you start to remove aliens, do it carefully, in stages, to prevent soil erosion. You may have to go back a few times to remove a particular alien that has germinated. It takes lots of monitoring and continual maintenance to keep a garden free of aliens. Once you get on top of it, managing alien invasive plants is much easier.
Methods of eradicating alien plants
Herbicides: using herbicides is essential because it greatly reduces the regrowth potential of most plants. Ask for advice from a reputable nursery or horticultural store. Check on the toxicity levels for humans and insects, selective versus non-selective and the residual effect of the herbicide. It is best to use a broad-leaf selective herbicide for most of the aliens and reduces the level of danger caused by spray drift that could kill natural grasses. Certain herbicides can remain active in soil for many years. Select a herbicide that is registered for the plants you wish to target. Carefully read the safety precautions and never use empty containers for carrying drinking water. Spray during the active growing season of the selected plants and never spray on a windy day.
Mechanical control: this can be done by physically removing the plant by either digging it out, stripping the bark, ring barking, or a drastic means – by using fire. If a seedling is very young, pulling it out is the easiest. Don’t snap off the stem as this will leave the roots in the ground and the plant will regrow. If you cut a large shrub to the ground and don’t remove the root base, use a non-selective herbicide to kill the roots by painting it on the cut areas. Take some fallen leaves from your garden and cover any exposed areas with the leaves to prevent weeds resprouting.
Biological: Using the plant’s natural enemies to control the spread. It will not eradicate the plants completely but help reduce the numbers.
Seven worst Alien plant invaders in eThekwini
Trees:
Tecoma stans (yellow bells): evergreen shrub to small tree that is highly invasive as it is spread by seed along road margins and freeways. It competes with the local flora and grows in disturbed areas. Indigenous to Mexico and the US. Category 1 invader.
Litsea glutinosa (Indian laurel): grows to about 10, and resembles an avocado pear. Indigenous to India and the Himalayas. Category 1, spread by seeds eaten by birds. Very invasive.
Melia azedarach (syringa berry): originates from India and produces lilac scented flowers that turn to orange-brown berries once pollinated. Toxic to children and livestock. Eaten by birds who disperse the seeds. Probably Durban’s most invasive tree.
Cinnamomum camphora (camphor tree): Native to China. Planted as a quick growing tree in South Africa, creating a huge problem in KwaZulu-Natal, seeds dispersed by birds. Crushed leaves have a camphor smell.
Schinus terebinthifolia (Brazilian pepper): this tree was planted as wind break for most sugar farms and are out of control in KZN. Red fruit eaten by birds, spreading the seeds.
Shrubs and creepers:
Lantana camara (tick-berry): probably the worst alien plant in South Africa. It is an untidy spreading shrub that grows to 2m in height. Covered in thorns along the stems with rough hairy leaves which are scented when crushed. It produces pink, red, orange, yellow and white flowers. Produces green fruits that turn black when ripe. Poisonous to humans but eaten by birds who disperse the seeds. Category 1.
Chromolaena odorata (Siam weed) indigenous to the Americas. Highly invasive. Seed dispersed by wind and animals. Easily removed physically but grows quickly from seed to maturity.
Solanum mauritianum (bugweed): highly invasive shrub in Durban which originates from South America. Grows into a large plant quickly, produces purple flowers that, once pollinated, produce orange fruits which are eaten by birds who distribute the seeds. Leaves and stems have white hairs. Easily removed when young by physically uprooting the plants.
Hedychium flavecens (yellow ginger): produce leaves that grow to 2m with a yellow fragrant flower. Seeds are dispersed by birds who feed on the fruit. Produce rhizomes that are hard to remove. Grown in many gardens as an ornamental. Category 1.
Anredera cordifolia (Madeira vine): Flowering creeper that has got into most gardens in Durban. Indigenous to South America, this succulent creeper smothers most plants and can break branches. The fragrant white flowers attract butterflies and bees that pollinate the flowers. Category 1. Remove physically.
Please ensure when planning a new garden that you remove alien invaders before you begin planting. If you don’t know what the plant is, please contact me or a nursery for help. We must work together in eradicating these plants before much of our natural habitats are destroyed.
Happy gardening.
- This article is sponsored by Chris Dalzell Landscapes, specialising in landscaping, consultation, plant broking and Botanical tours. For answers to questions, email [email protected]
The Independent on Saturday