Alien plants: The threats and the opportunities


The Agulhas Plain, along with the rest of the world, celebrates World Environment Month in June. But the celebrations are tainted by the challenges facing land users on the Plain: not least, the threat of invasive alien plants. Landowners, conservationists and government departments alike refer to it as probably the biggest threat to our water security and biodiversity, particularly in the fynbos biome.

According to a recent study by the Council for Scientific and Industrial Research (CSIR), alien plants result in a net loss of value of nearly R700-million a year in the Cape Floristic Region, with this figure rising all the time. There are more than 200 plant species that invade natural ecosystems in the country, from the Acacia species to myrtle to hakea. These plants use around seven percent of South Africa's water flow every year; they raise the risk of wildfires, and they thus increase the emissions of carbon dioxide into the atmosphere.

The Agulhas Plain, an area of around 270 000 hectares around the southern tip of Africa, is no exception. While the region hosts the threatened lowland fynbos and critically endangered renosterveld, it is 23 percent invaded by alien species, according to a study by David le Maitre of the CSIR and Megan Nowell (MSc, currently studying in Italy). This not only has ecological impacts, but also limits the potential for economic development in the area. The study found that the 25 000 people that are employed in indigenous flower harvesting (according to a survey in 2000), could be increased if land that is currently infested became available for other land use options, such as for growing indigenous fynbos.

It also found that an additional net income of R870 000 could be made from flower harvesting and other fynbos products, were the land to be restored to its natural state and were there markets for these flowers. At the same time, alien clearing in the region could create more than one million person days of work.

The study, which was summarised with the help of Helanya Fourie of the Western Cape Department of Agriculture, also assesses the clearing of plants to produce biomass for energy, as well as the option of growing certain alien plants in order to cut them down and use them in the creation of energy. They write, "By providing a financial incentive for alien plant removal, woodchip production from invasive biomass for bioenergy generation could add value." However, there are risks associated with planting alien species, not least the potential loss of land of high biodiversity value or land of agricultural value when planting the biomass.

According to Fourie and Le Maitre, "The threat to biodiversity and food security that is associated with introducing crop species for bioenergy can be minimised if project areas are selected discerningly. Aspects to consider include the cost of restoring an invaded or transformed site to its natural state, the conservation value of the natural biodiversity (in this case fynbos and the associated ecosystem), and the opportunity cost of the ecosystem goods and services that will be foregone if bioenergy crops are planted."

Their conclusion is that both options offer opportunities, if they're implemented properly. What's more, they warn policymakers that the value of ecosystem services may increase, as certain ecosystem services become scarcer. As such, decision-makers should bear this in mind when deciding the way forward. This will give land users and conservationists hope that inhabitants will stop taking well-functioning ecosystems for granted. And will give direct incentives to those managing both public and private properties to clear their lands of alien plants and to manage them wisely.

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