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Alien Invader Plants
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Alien Plant Watch February 2004Jean MoorePrickly ProblemsI have had a number of enquiries just lately from people needing advice on how to tackle various thorny invaders. It’s one thing to wade into a patch of Chromalaena odorata, or Tithonia diversifolia but just imagine being faced with wall-to-wall thickets of bramble (Rubus cuneifolius) or Lantana (Lantana camara), or metres and metres of tangled Mauritius thorn (Caesalpinia decapetala), Pereskia (Pereskia aculeata) or Jointed cactus (opuntia aurantiaca) high in the canopy of your favourite trees!!!! Unfortunately, all these prickly invaders are difficult to manage and eradication is usually laborious and expensive. In some cases where a number of factors combine to make access to the entire affected area very difficult if not impossible, eradication is probably a pipe dream and the best that can be hoped for is to limit further spread by containing the existing invasion as much as possible. Because of the physical difficulties involved when dealing with these prickly problems, careful thought, innovative methods and real tenacity of purpose are often needed if any success is to be achieved. If you are one of the unlucky people faced with any of these invaders on your property, it is essential that you plan your control programme carefully. Start with smaller, isolated patches and accessible individual plants. Match all available methods for control of that species to your specific situation until you arrive at an integrated programme suited to your needs. If, for example, you are faced with a 50 square metre impenetrable patch of bramble, decide whether you can afford “Brush-off” for a once-off treatment, or whether one of the other registered herbicides would be better. If you do not have access to a tractor and boom sprayer, flatten “pathways” through the bramble using a drum, or place sheets of corrugated iron strategically and work systematically so that your handheld sprayer reaches all the plants. Never spray before November and wait for the plants to be in berry. Remember, there are three stages of weed control: initial control, follow-up and maintenance., but with many of these pricklies, you need follow-up, follow-up and follow-up before you get to “maintenance”. Luckily, Biological control in South Africa for many invader species is progressing by leaps and bounds. There are dozens of people working very hard to ensure that our worst invaders are at least safely suppressed by natural enemies if not entirely eradicated. The Mauritius Thorn Seed-Weevil, for example, attacks mature seeds that have already fallen from the pod, so will help decrease the number of viable seeds left in an area after clearing. Both adults and larvae of the Pereskia Flea Beetle feed on pereskia leaves, reducing the weeds canopy and size of the weed mat and allowing desirable plants to grow, and making conventional control easier. Despite the difficulties involved, biological control agents for Lantana are out there helping suppress the spread of this weed and research is ongoing for more effective agents. (Contact Debbie Muir at 033 355 9413 if you need to know more about this fascinating topic.) A SPECIAL PLEA: POM-POM WEED IS SPREADING OUT OF CONTROL. PLEASE HELP ERADICATE IT BEFORE IT IS TOO LATE. STOP IT SEEDING NOW! SEE OUR HOME PAGE IDENTIFICATION
N3: A lily corridor or a road for environmental education?Eden Wildy, WESSA / Hillside Aluminium Alien Invader Plants ProjectLilium formosanum, the St Joseph’s trumpet or Formosa lily, has emerged along one of KwaZulu-Natal’s major highways and using this as a conduit to spread, invading grasslands with impunity. Already invaded are the road reserves between Westville and Howick. This Category Three invader plant has the potential to outcompete and replace indigenous species. The little grassland that we have left is rapidly being degraded. Nevertheless, many avid home gardeners were up at in arms when Regulation 15 of CARA was amended in 2001, listing the Formosa lily as a declared invader plant. The good news is that indigenous alternatives exist. For the ecologically minded home gardener the following can be planted and grown in place of this potential threat to KwaZulu-Natal’s environment: · Orange River Lily (Crinum bulbispermum) · River Lily (Crinum macowanii) · Moore’s Crinum (Crinum moorei) · Large Yellow Wild Hibiscus (Hibiscus calyphyllus) However, many home gardeners – and the general public – instinctively resist when they are admonished or lectured. The manner of the delivery is, irrespective of the underlying good intentions, often to blame. In extreme cases it can degenerate into public squabbling via the printed media and word of mouth. A primary reason for this is the lack of environmental education. Public education is an essential part of prevention and management programmes. Public awareness and support can increase greatly the success of projects aimed to protect and save biodiversity. Education should focus on raising the awareness of the reasons for the restrictions, regulatory actions, and the environmental and economic risks involved. So what are they relative to the Formosa lily? As already mentioned, the major concern with respect to this species is its potential ability to spread naturally into grassland, moist sites, road reserves, and plantations. A landowner, with this species on their property may retain the plant provided they proactively manage the specimen. Failure to do so may result in a directive to ‘control’ the plant and failure to comply with a directive would lead to a court summons. The species may not be planted, propagated, imported or traded. The economic and environmental risks if we do not succeed are intrinsically linked. The grassland biome is the most endangered within South Africa. Less than 2% of what remains is formally conserved and for every species loss the propensity for economic cost and environmental damage grows. Is the Formosa lily really worth this?
Know Thy EnemyEden Wildy, WESSA / Hillside Aluminium Alien Invader Plants Project.One of the major obstacles in campaigning against alien weeds and alien invader species is trying to dispel the multitude of myths and misconceptions that surround the control and eradication of such species. People active in the various alien plant eradication initiatives are not anti exotic plants per se, but exotic plants that have shown an ability to invade natural or semi-natural habitats. There is a noticeable distinction between ‘benign exotics” and “alien invader plants”, one that is recognised, and appreciated, by those involved in the campaign against alien weeds and invader plants. Over 9000 plant species have been introduced to South Africa. Of these, 198 species have either been declared weeds or alien invader plants. This is little more than 2% of the exotic flora within South Africa. These 198 species have been targeted due to their ability to spread naturally, threaten biodiversity, and significantly (and detrimentally) alter an ecosystem. From a nature conservation perspective, the mere presence of an alien invader plant species is a threat. An ecological, social, and economic reason why alien invader plants are detrimental is due to the amount of water they draw from the water table. n KwaZulu-Natal, alien invader plants use approximately 576 million m3 per annum more than the natural vegetation they have invaded and replaced. How well do we know our enemy? There is a high probability that if you don’t have an alien weed or invader plant in your garden, your neighbour will. This is not due to any form of social malady but due to a lack of information combined with poor communication channels. In 2002, WESSA undertakes to improve both the quality of information pertaining to this issue and to improve communication to the community. Together we may be able to conserve our natural heritage for our children and our children’s children.
Rehabilitation: the forgotten goal in strategies for the control and eradication of alien invader plants.Eden Wildy, WESSA / Hillside Aluminium Alien Invader Plants Project.The control and eradication of alien invader plants is beginning to receive the attention it requires. Nevertheless, the objective to eradicate category one alien invader plants and control category two and three plants should not be seen as an end unto itself but rather as a means towards an end. The ultimate goal of every strategy in the control and eradication of alien invader plants must be the restoration or rehabilitation of the land. It is essential that land users and landowners accept that once time, money and effort have been spent on control and eradication strategies, they are committed to rehabilitating the area. If such a commitment is not forthcoming then there is a high chance that the land will be subject to reinvasion. Two forms of rehabilitation are generally identified, namely: rehabilitation and restoration. Rehabilitation is defined in terms of making the land useful again. This may be achieved by creating a useful, productive or attractive plant cover such as a pasture for the grazing of livestock and also by stopping or avoiding further degradation on surrounding land. Restoration is where the objective is to return the land as close as possible to its original condition. For example, such a strategy may involve planting indigenous pioneer tree species in a degraded forest. Whichever is decided upon, follow-up control is essential. Follow-up control requires a monitoring programme to detect and remove alien seedlings until the viable invasive seed bank is exhausted and indigenous plants are once again naturally re-establishing. Failure to perform the necessary follow-up control and rehabilitation creates the environment in which the cleared land may revert back to the previous state of infestation or even worse.
Weeds and Economics.Eden Wildy, WESSA / Hillside Aluminium Alien Invader Plants Project.The control and eradication of alien weeds and invader plants has a disturbing tendency to be viewed by a significant percentage of the population as an overreaction to what is seen as primarily an ecological problem and a subjective one at that. An ecosystem is, after all, dynamic and change is inevitable. Ecological arguments justifying the campaign to control and eradicate alien weeds and invader plants are often misconstrued as the dialogue of tree-huggers. Nevertheless, an attitude of indifference quickly turns to interest when the dialect moves from ecology to the language of economics. And a very strong economic imperative exists to combat alien weeds and invader plants. Alien weeds and invader plants incur economic costs. An official estimate suggests that the costs of mounting a one-year, ‘once off’ eradication campaign would be R6.97 billion, including the necessary follow-up costs. This, however, is impossible in practice. If alien weeds and invader plants are conservatively estimated to spread at 5% per annum, a 20-year programme would cost approximately R600 million per annum and the total cost (at net present value) would be R5.44 billion. While the cost of clearance is high, the alternative may be even more costly. Economists use the term ‘opportunity costs’ for losses incurred through certain choices made over others, including ignorance and inaction. For alien weeds and invader plants, or more precisely the neglect of the problems posed by alien weeds and invader plants, these costs may well prove to be very high. For example, a delay of 10 years in launching such a programme would increase the projected costs by 55%. Furthermore, increased costs may be expected in the agricultural sector as the cost of managing land and livestock rises due to such factors as bush encroachment and livestock poisoning. Communities living in areas infested by alien invader plant species may also experience health problems. Some species are toxic to humans, e.g. lantana, particularly among children, has reportedly caused death through neuro-circulatory collapse. Symptoms include stomach and intestinal irritation, muscular weakness and circulatory collapse. Hospitalisation is essential. Thus, the control and eradication of alien weeds and invader plants has far-reaching economic, as well as ecological and social, implications. This is encapsulated in the effect that alien weeds and invader plants have on South Africa’s water resource. In KwaZulu-Natal alone, alien weeds and invader plants use approximately 576 million m3 per annum more than the natural vegetation they have invaded or replaced. Tree-hugging? Perhaps. Concern for our future economic, ecological and social quality of life? Definitely. This page was last edited on 23 April, 2006 |
