Arne Witt

Biofuels and invasive species from an African perspective – a review

A large number of proposed biofuel crops share the same traits as known invasive plant species, many of which are already present in Africa and include species such as Prosopis glandulosa Torrey (Mimosaceae), P. juliflora (Sw.) DC, Leucaena leucocephala (Lam.) de Wit (Mimosaceae), Azadirachta indica A. Juss. (Meliaceae), and others. In this paper, we mainly assess the impacts of invasive Prosopis species in Africa, particularly in Kenya and South Africa. Introduced Prosopis species have invaded over 4 million hectares in Africa, threatening crop and pasture production, reducing underground water reserves, and displacing native plant and animal species. This has major implications for millions of people who depend on natural resources for their survival. It is therefore suggested that known invasive or potentially invasive plant species not be introduced to countries or regions for biofuel production. If (after a stringent cost–benefit analysis) the introduction of a potentially invasive species is deemed critical for economic development and the benefits clearly outweigh the potential costs, countries should endeavour to abide by the Principles and Criteria for Sustainable Biofuel Production developed by the Roundtable on Sustainable Biofuels.

The impacts of some classical biological control successes.

We differentiate between the success of a classical biological control programme and its impact; the former addressing the completed implementation of the steps of a biological control programme, and the anticipated reduction of the target pest, and the latter addressing the societal and environmental benefits of control of the target pest. We provide ten case studies in which CABI has played a role to illustrate aspects of success and impact for biological control programmes against insects pests and weeds: cassava mealybug (Phenacoccus manihoti), mango mealybug (Rastrococcus invadens), pink hibiscus mealybug (Maconellicoccus hirsutus), orthezia bug (Insignorthezia insignis), brown peach aphid (Pterochloroides persicae), banana skipper (Erionota torus), black sage (Varronia curassavica), rubber vine (Cryptostegia grandiflora), leafy spurge (Euphorbia esula) and water hyacinth (Eichhornia crassipes). In light of these we discuss the assessment of success and impact of biological control programmes, why these aspects are often not adequately addressed, how they might be retroactively addressed and the implications for donor-funding of biological control programmes for developing countries.

Chromolaena odorata (Siam weed) in eastern Africa: distribution and socio-ecological impacts

Invasive alien plant species such as Chromolaena odorata have negative impacts on biodiversity, ecosystem services and human well-being. Ecological impacts of this shrub are relatively well understood, but its impacts on local livelihoods and perceptions are poorly documented. We mapped C. odorata distribution in eastern Africa (Ethiopia, Kenya, Rwanda, Tanzania and Uganda) and compared perceptions and quantified the impacts of this species across Tanzanian villages with varying degrees of invasion density. Data were collected through 240 household questionnaires. Results indicate that C. odorata is a relatively new invader that already has severe negative impacts and is threatening livelihoods and the environment. Impacts include reductions in native biodiversity and the amount of available forage for livestock, reduced crop and water yields, and impaired mobility. Continued spread will cause additional negative impacts on poor rural communities. Implementation of a biological control programme targeting C. odorata is needed as a cost effective management approach along with other control and restoration measures.

Icons in Peril: Invasive Alien Plants in African Protected Areas

Protected areas in Africa are global conservation icons, attracting millions of tourists a year. However, these areas are being threatened by a growing human population making increasing demands on the natural capitol being conserved. Moreover, global environmental change, of which biological invasions are a key concern, pose significant threats to the function of ecosystems and their constituents. Other than in a few regions, primarily in South Africa, little is known about alien plant invasions in protected areas across the continent. In order to present a first approximation of the threat of plant invasions to protected areas across Africa, we present the information we could find by drawing on published literature, grey literature and personal observations. We also present six case studies from prominent protected areas across Kenya, Tanzania and South Africa. These case studies aim to illustrate what is known in different regions and the key concerns and management approaches, thereby providing examples that may facilitate shared learning. Where information is available it suggests that some species are likely to be widespread, impacting severely on indigenous species diversity. If protected areas are to be successful in carrying out their mandate of biodiversity conservation, and increasingly, revenue creation, long-term management of invasive plants is essential. However, in developing countries, which characterise much of Africa, resources are severely lacking. Where funds are available for conservation these are often channelled to other aspects of protected area management, such as anti-poaching. Protected areas in Africa include a number of unique attributes that can provide natural laboratories for research on basic ecological principles of invasions, while the research can, in turn, contribute directly to the needs of the protected area agencies.

Distribution of the invasive alien weed, Lantana camara, and its ecological and livelihood impacts in eastern Africa

Lantana camara (lantana) is a major invasive shrub globally, impacting upon biodiversity, economies, ecosystem services, and driving socio-ecological change. The aim of this study was to determine the current and potential distribution of lantana in eastern Africa and its livelihood impacts in one region in Uganda. Data were collected by means of roadside surveys, and then compared with potential distributions based on ecoclimatic models. Household interviews were conducted to understand the impacts of lantana on local livelihoods. Lantana is currently widespread in eastern Africa, and has the potential to spread, especially in Tanzania. According to 40% of respondents, lantana reduced the amount of forage available to livestock by more than 50%, while one-third of those interviewed reported a 26–50% reduction in crop yields. Lantana invasions also cost individual households substantial amounts of money (US

Would the control of invasive alien plants reduce malaria transmission? A review

400–500 per annum). Furthermore, lantana reduced the availability of natural resources, such as native medicinal plants, and hindered the movement of people and livestock. Based on the potential distribution of lantana, and its current impacts, we suggest that an integrated management strategy be developed and implemented, including the introduction of additional biological control agents to reduce the negative effects of lantana on local livelihoods.

Use of Non-native Species for Poverty Alleviation in Developing Economies

Vector control has been the most effective preventive measure against malaria and other vector-borne diseases. However, due to concerns such as insecticide resistance and budget shortfalls, an integrated control approach will be required to ensure sustainable, long-term effectiveness. An integrated management strategy should entail some aspects of environmental management, relying on coordination between various scientific disciplines. Here, we review one such environmental control tactic: invasive alien plant management. This covers salient plant-mosquito interactions for both terrestrial and aquatic invasive plants and how these affect a vector’s ability to transmit malaria. Invasive plants tend to have longer flowering durations, more vigorous growth, and their spread can result in an increase in biomass, particularly in areas where previously little vegetation existed. Some invasive alien plants provide shelter or resting sites for adult mosquitoes and are also attractive nectar-producing hosts, enhancing their vectorial capacity. We conclude that these plants may increase malaria transmission rates in certain environments, though many questions still need to be answered, to determine how often this conclusion holds. However, in the case of aquatic invasive plants, available evidence suggests that the management of these plants would contribute to malaria control. We also examine and review the opportunities for large-scale invasive alien plant management, including options for biological control. Finally, we highlight the research priorities that must be addressed in order to ensure that integrated vector and invasive alien plant management operate in a synergistic fashion.

Risk assessment, eradication, and biological control: global efforts to limit Australian acacia invasions

For decades, development agencies, donors, and others have worked to improve the social and economic reality of people living in the developing world through inputs into the agricultural and fisheries sectors. To improve agricultural production and stem land degradation, often brought about by unsustainable land use practices, non-native tree and shrub species have been introduced, especially to Africa and Asia. To feed rapidly growing populations in these regions, non-native fish species have also been introduced to supplement existing protein sources, which are rapidly being depleted as a result of overexploitation and pollution. Many of these non-native species provide significant benefits to poor communities, but there are also costs associated with these introductions when species escape cultivation or culturing and establish populations in the wild. These “escapees” can have significant negative impacts on biodiversity and ecosystem function, negating their benefits, especially when measured at a landscape or national level. The failure of many development agencies and others to seek holistic or win–win solutions that benefit all sectors, or do not have negative impacts on others, will, in the final analysis, be to the detriment of the millions of poor communities they have tried to assist. The unfortunate reality is that many donors and development agencies have failed to recognise or acknowledge that cultured organisms can have significant impacts on ecosystems and human health should they escape and establish invasive populations.