Ross T. Shackleton

Prosopis: a global assessment of the biogeography, benefits, impacts and management of one of the world's worst woody invasive plant taxa

Taxa from the genus Prosopis are widespread invasive aliens across the globe. Numerous species have contentious issues surrounding them as they provide both benefits and harm. Prosopis taxa are currently naturalised or invasive in 103 countries and are bioclimatically suitable for many more. There are numerous management practices available to control Prosopis invasions, each with their benefits and costs, however, in most areas management has had only limited success. There is need for more research to improve understanding and management success and for countries to develop strategic plants to guide managed in the future.

Use of non-timber forest products from invasive alien Prosopis species (mesquite) and native trees in South Africa: implications for management

BackgroundProsopis species have been introduced to many areas outside their native range to provide benefits to local communities. Several Prosopis species and their hybrids (hereafter “mesquite”) have, however, become naturalised and invasive and now generate substantial costs. Management options are limited because of the complex conflicts of interest regarding benefits and costs. Management policies and strategies must take account of such conflicts, but further insights are needed on the dimensions of uses and impacts before such information can be usefully applied. Current policy in South Africa allows for the growth and use of mesquite in one province, but not in others where its control is mandatory. We report on a study to quantify the direct use and perceptions of non-timber forest products (NTFPs) from mesquite and native trees in South Africa.MethodsSemi-structures household interviews were conducted with various stakeholder groups to identify what tree products are used, to ascertain amounts used as well as to gauge perceptions of natural resource use between different tree species and use over time.ResultsThe direct household use value of native trees was higher than that of mesquite, and local stakeholders attached greater value to products from native trees than from mesquite. Therefore, native trees are and will still be preferentially harvested, and mesquite is unlikely to offer protection to native species by providing an alternative source of products. Mesquite pods do, however, provide valuable additional resources (fodder and medicinal products). The use of both native trees and mesquite is decreasing as the incomes of poorer households rise and as alternative energy sources become available. The benefits and reliance on mesquite are not as high as previously assumed and the impacts from mesquite invasions create large problems for local communities.ConclusionThis study provides further evidence that the impacts of mesquite exceed the benefits, lending support for a policy to reduce negative impacts.

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.

The role of invasive alien species in shaping local livelihoods and human well-being: A review

Invasive alien species are a well-recognised driver of social-ecological change globally. Much research has focused on ecological impacts, but the role of invasive species for livelihoods and human well-being is less well known. Understanding the effects (benefits and costs) of invasive species on livelihoods and human well-being is important for guiding policy formulation and management. Here we review the literature on the role of invasive species in livelihoods to assess what is known, identify knowledge gaps and provide recommendations for future research. Literature was collected using key word searches and included both journal publications and grey literature. Slightly less than half (48%) of species studied had both substantial positive and negative impacts on local livelihoods (e.g. Australian Acacia spp. species; Camelus dromedaries; Lantana camara; Prosopis spp.), with 37% inducing mainly costs (Chromolaena odorata; Lissachatina fulica; Opuntia stricta) and 16% producing mainly benefits (Opuntia ficus-indica; Acacia spp.). Some species, such as Acacia dealbata, fell into different categories depending on the social-ecological context. Key benefits or services included the provision of fuelwood, fodder, timber and food products for local households communities and to a lesser extent supporting and regulating services such as soil improvement and shade. A number of species also provided cultural services such as recreation and spiritual values and provided many with an opportunity to earn a cash income. However, invasive species also harm livelihoods and increase vulnerability through encroaching on land and reducing mobility or access. They can also decrease the supply of natural resources used by households and reduce agricultural production (livestock and/or crops) which can result in losses of income and increased vulnerability. Furthermore, some invasive species were seen to have negative implications for human health and safety and reduce the cultural value of landscapes. Economic impacts on livelihoods as a result of invasive species were highly variable and very dependent on the social-ecological contexts. These negative implications can reduce resilience and adaptive capacity of households and communities thus increasing their vulnerability to change. Drawing on case studies we highlight that efforts for managing invasive species need to safeguard livelihood benefits while mitigating negative impacts. In concluding we highlight future research and policy needs on the topic of invasive species, livelihoods and human well-being.

Explaining people's perceptions of invasive alien species: A conceptual framework

Human perceptions of nature and the environment are increasingly being recognised as important for environmental management and conservation. Understanding peoples perceptions is crucial for understanding behaviour and developing effective management strategies to maintain, preserve and improve biodiversity, ecosystem services and human well-being. As an interdisciplinary team, we produced a synthesis of the key factors that influence peoples perceptions of invasive alien species, and ordered them in a conceptual framework. In a context of considerable complexity and variation across time and space, we identified six broad-scale dimensions: (1) attributes of the individual perceiving the invasive alien species; (2) characteristics of the invasive alien species itself; (3) effects of the invasion (including negative and positive impacts, i.e. benefits and costs); (4) socio-cultural context; (5) landscape context; and (6) institutional and policy context. A number of underlying and facilitating aspects for each of these six overarching dimensions are also identified and discussed. Synthesising and understanding the main factors that influence peoples perceptions is useful to guide future research, to facilitate dialogue and negotiation between actors, and to aid management and policy formulation and governance of invasive alien species. This can help to circumvent and mitigate conflicts, support prioritisation plans, improve stakeholder engagement platforms, and implement control measures.

Stakeholder engagement in the study and management of invasive alien species

Invasive alien species are a major driver of global environmental change and a range of management interventions are needed to manage their effects on biodiversity, ecosystem services, human well-being and local livelihoods. Stakeholder engagement is widely advocated to integrate diverse knowledge and perspectives in the management of invasive species and to deal with potential conflicts of interest. We reviewed the literature in the ISI Web of Science on stakeholder engagement (the process of involving stakeholders (actors) in decision making, management actions and knowledge creation) in invasion science to assess and understand what has been done (looking at approaches and methodologies used, stakeholders involved, and outcomes from engagement) and to make recommendations for future work. Research on stakeholder engagement in invasion science has increased over the last decade, helping to improve scientific knowledge and contributing towards policy formulation and co-implementation of management. However, many challenges remain and engagement could be made more effective. For example, most studies engage only one stakeholder group passively using questionnaires, primarily for assessing local knowledge and perceptions. Although useful for management and policy planning, these stakeholders are not active participants and there is no two-way flow of knowledge. To make stakeholder involvement more useful, we encourage more integrative and collaborative engagement to (1) improve co-design, co-creation and co-implementation of research and management actions; (2) promote social learning and provide feedback to stakeholders; (3) enhance collaboration and partnerships beyond the natural sciences and academia (interdisciplinary and transdisciplinary collaboration); and (4) discuss some practical and policy suggestions for improving stakeholder engagement in invasion science research and management. This will help facilitate different stakeholders to work better together, allowing problems associated with biological invasions to be tackled more holistically and successfully.

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

The impact of invasive aquatic plants on ecosystem services and human well-being in Wular Lake, India

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.

Socio-Environmental Systems (SES) Research : What have we learned and how can we use this information in future research programs

Alien invasive species cause significant impacts on ecosystems and economies, but the impacts on human well-being and livelihoods are less well known. Negative impacts can be particularly severe when caused by floating aquatic plants, which can reduce access to freshwater for extraction and navigation, reduce the harvest of fish and other resources, and change water cycling and chemistry. This paper reviews and discusses some of these impacts globally and then concentrates on the case study of Wular Lake, India. Wular is the largest freshwater lake in Jammu and Kashmir state and is highly important for local livelihoods through the provision of a range of services, including fish and edible aquatic plants, and water to local communities. The supply of these services has decreased due to a long history of environmental degradation, and recent invasions by the floating plants Azolla cristata and Alternanthera philoxerodies (alligator weed) have further impacted human well-being. Here, we review the published literature about these invasions, present information from interviews with locals living near Wular Lake, and review the global literature about invasive floating plant species to assess the present and predict the future impacts of these species. We find that the implications of these invasions for livelihoods reliant on lake resources and services provide good justification for management efforts. We discuss some options and challenges to such a management program.