Invasive alien species should not be used in restoring degraded landscapes as their costs outweigh their benefits, experts say.
Invasive alien species, according to the Convention on Biological Diversity, are plants, animals and other organisms that are non-native to an ecosystem, and may adversely affect human health and the environment, including decline or elimination of native species.
In the late 1970s and early 1980s the group of closely-related woody plant species and hybrids known as Prosopis were seen as a ‘saviour’ for millions of pastoralists and agro-pastoralists in East Africa whose very livelihoods were threatened by the degradation of dryland ecosystems spurred on by overgrazing, and by deforestation and a shortage of firewood.
CABI scientists have joined an international team of experts who suggest that the large-scale management of a range of some invasive plants could hold the key to reducing the spread of deadly malaria.
Dr Arne Witt and Dr Sean Murphy worked with scientists from the University of Illinois, The Ohio State University and the Fundación para el Estudio de Especies Invasivas (FuEDEI) in Argentina, to conduct a review of existing studies which looked at how mosquitoes are attracted to both land and water-based invasive plants such as water hyacinth, floating pennywort and prosopis and how best these invasive plants can be managed.
Is promoting the utilisation of invasive non-native species for commercial or other uses e.g. as a feed for livestock, use as a fuel or to produce biogas, a help or a hindrance to their control?
A view from Arne Witt, CABI Regional Coordinator, Invasives (Africa & Asia):
Promoting the utilization of any invasive non-native species (INNS) has largely contributed to their spread, especially in most developing countries which don’t have the capacity to develop and implement effective integrated management strategies. Utilization as a control can only be effective if it forms part of an integrated management plan – on its own it merely exacerbates the problem. There are many examples of where INNS have been intentionally spread by individuals because they have been led to believe that they can enrich themselves by growing and then utilizing an INNS – at low densities many INNS are beneficial, but it does not stay that way for very long – short-term benefits but long-term costs.
One needs to remember that utilization works from “inside out” whereas “control or management” works from “outside-in”. In other words, the most cost-effective way to utilize an INNS is at the largest and densest infestations. As such you would build your biogas plant or sawmill in an area where the costs with regard to transport are lowest. In addition, you would not “eradicate” any of the plants you utilize – it is expensive and time-consuming to do so and why would you want to anyway, you want a renewable resource, so getting the plants to coppice, so that you can use them again in the future, is exactly what you want. This is largely what is happening in Africa – those utilizing prosopis for charcoal do not apply herbicide to the cut stumps or dig out the rootstock – they want the plants to coppice. The same happens in India with regard to the utilization of lantana – communities don’t kill the lantana, they allow it to coppice. In addition, it does not make economic sense to utilize plants growing individually or in small pockets away from these dense infestations, especially in developing countries where we have poor infrastructure. For a control/management strategy to be effective we need to work from the “outside-in”, removing individual plants or small isolated stands first before moving onto the dense stands – utilization works in the opposite way which is why it is ineffective as a management strategy on its own.