Aim Australian acacias (1012 recognized species native to Australia, which were previously grouped in Acacia subgenus Phyllodineae) have been moved extensively around the world by humans over the past 250 years. This has created the opportunity to explore how evolutionary, ecological, historical and sociological factors interact to affect the distribution, usage, invasiveness and perceptions of a globally important group of plants. This editorial provides the background for the 20 papers in this special issue of Diversity and Distributions that focusses on the global cross-disciplinary experiment of introduced Australian acacias.Location Australia and global.Methods The papers of the special issue are discussed in the context of a unified framework for biological invasions. Distributions of species were mapped across Australia, their representation in bioclimatic zones examined and the potential global distribution of the group modelled. By collating a variety of different lists, we determined which Australian acacias have reached different stages in the introduction-naturalization-invasion continuum in different parts of the world. Paradigms and key research questions relating to barriers to invasion, stages of invasion and management perceptions are sketched.Results According to our global database of Australian acacia records, 386 species have been moved outside Australia by human agency, 71 species are naturalized or weedy, and 23 are unequivocally invasive. Climatic models suggest that about a third of the world's land surface is climatically suitable for Australian acacias. Many species are commercially important crops or are useful for other purposes and have been extensively planted, and many different human perceptions of Australian acacias exist in different parts of the world. The papers in the special issue cover all the barriers, stages and processes that define biological invasions and touch on many aspects: history and the human dimension; aspects of the species pool; species traits; biotic interactions; climate and niche; and management.Main conclusions Australian acacias are an excellent model group for examining interactions between evolutionary, ecological and socio-economic drivers of species introductions. New insights have emerged on the biological, ecological and evolutionary correlates of naturalization and invasion, but human usage factors permeate all explanatory models. Understanding and managing introduced Australian acacias requires a fundamental and integrative appreciation of both intrinsic (e.g. species traits) and extrinsic (e.g. human usage and perceptions) aspects.

Aim Anthropogenic introductions of Australian Acacia spp. that become classed as alien invasive species have consequences besides the physical, spatial and ecological: there are also cultural, ethical and political considerations that demand attention from scholars in the humanities and social sciences. As practitioners in these disciplines, our aim is to reflect upon some of the social and conceptual ideas and attitudes relating to the spread of Australian Acacia spp. around the world. We therefore provide a longer-term historical and philosophical perspective using South Africa as a key example. We explain some of the cultural aspects of Australian acacias, relating them to history, philosophy and societal ideas that were once, or indeed remain, important, either regarding their exportation from Australia or their importation into other countries. Focussing principally on South Africa and Australia but including brief references to other locations, we augment the literature by making connections between acacia introductions and environmental ethics and aesthetics, national and environmental history and symbolic and other discourses. We evaluate a number of the cultural and philosophical dimensions of invasion biology as a societal response and explicate the interesting contradiction of Australian acacia introductions as simultaneously economically valuable and environmentally transformative in South Africa.Location South Africa, Australia, with references to other parts of the world.Methods This paper has been written by an interdisciplinary team (two historians, two geographers, a philosopher and an ecologist) and is conceptual and historical, conforming in language and structure to the humanities style. It relies on published and unpublished literature from this disciplinary domain and the critical evaluation of these sources.Results Many Acacia spp. from Australia have been introduced around the world, generally guided in different eras by a variety of overarching mindsets, including the colonial ethos of 'improvement' (1800s to mid 1900s), an economically driven mindset of 'national development ' (1900s), by a people-centred frame combining concerns of environment and livelihood in 'sustainable development ' (1980s onwards), and an aesthetic ethos of ornamental planting that surfaces in all periods. The newest ethos of controlling or managing alien invasive species, a normative attitude deriving from the burgeoning of invasion biology, has more recently shaped the ideology of these plant exchanges and sharpened the focus on species that may be simultaneously both weeds and commercially valuable crops. Our perspective from the humanities and social sciences calls for a more transparent approach that clearly acknowledges such contradictions.Main conclusions We conclude that the global experiment of human-mediated Australian acacia introductions raises a number of issues that reflect changing societal concerns and demand attention from scholars in disciplines apart from

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