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South Africa has a major problem with invasive plant species. Many species have long residence times, are well established, and have large invasive ranges, whereas others are still in the early stages of invasion. Predicting the full extent of invasions for species that have only recently started spreading is important for guiding management strategies. Ailanthus altissima is a widespread invasive species in many parts of the world. Although it has had a long residence time in South Africa, it is yet to replicate the extent of invasiveness and major impacts reported for the species in other parts of its adventive range. We mapped the countries in which A . altissima has been reported and evaluated the invasion status of the species in each (i.e. the position of the species on the introduction-naturalization-invasion continuum as conceptualized by Richardson and Pysek, 2012). We then mapped the current distribution in more detail for South Africa. The species is known to be present in at least 51 countries and is invasive in 23 countries. Ailanthus altissima is present in all South African provinces except Limpopo and is most common and abundant in the Western Cape, Gauteng, Eastern Cape, and the Free State. We applied species distribution modelling using global distribution data to determine parts of the world, and in particular regions within South Africa, that are climatically suitable for the species. Large parts of Africa are potentially invasible by this species. Seven regions in South Africa were identified as high-risk areas for invasion by A . altissima . The species is already far too widespread in South Africa for eradication at the national scale to be feasible. A national strategy for managing the species should focus on: 1) early detection and rapid response in areas identified as climatically suitable and where the species is not already present; and 2) local and regional-scale initiatives based on objective prioritization in terms of feasibility of management success and asset protection.

Techniques of conversation analysis are employed to reach a better understanding of the interactional competencies of young children. Drawing on audio–video recordings of mother–child interactions, this paper examines laughter by young children after questions by the child's mother. It is argued that by laughing the child is showing an orientation to the conditional relevance of a second pair part of an adjacency pair on the production of a first pair part. It is argued that possible bases for young children using laughter after a question are the child's inability to answer a question in full, and their unwillingness to do so. The children studied are in the second year of life and are making the transition from the single to multiword stage. All participants are native speakers of English and speak English throughout the recordings.

Repetition poses certain problems for pragmatics, as evidenced by Sperber and Wilson's claim that “the effects of repetition on utterance interpretation are by no means constant”. This is particularly apposite when we examine repetitions produced in naturally occurring talk. As part of an ongoing study of how phonetics relates to the dynamic evolution of meaning within the sequential organisation of talk-in-interaction, we present a detailed phonetic and pragmatic analysis of a particular kind of self-repetition. The practice of repetition we are concerned with exhibits a range of forms: “have another go tomorrow … have another go tomorrow”, “it might do … it might do”, “it's a shame … it's a shame”. The approach we adopt emphasises the necessity of exploring participants’ displayed understandings of pragmatic inferences and attempts not to prejudge the relevance of phonetic (prosodic) parameters. The analysis reveals that speakers draw on a range of phonetic features, including tempo and loudness as well as pitch, in designing these repetitions. The pragmatic function of repetitions designed in this way is to close sequences of talk. Our findings raise a number of theoretical and methodological issues surrounding the prosody–pragmatics interface and participants’ understanding of naturally occurring discourse.

The migration behaviour of americium through Boom Clay, which is rich in organic matter, has been investigated by complexing 241 Am with 14 C-labelled Boom Clay natural organic matter (NOM) and passing the resulting 241 Am- 14 CNOM through undisturbed Boom Clay cores contained in columns. In the presence of soluble organic matter, the total concentration of Am in solution increases several orders of magnitude above the solubility limit due to NOM complexation/colloids formation which could lead to an increased americium mobility in Boom Clay. The mobility of these complexes depends strongly on their stability and on their interaction with the solid phase (sorption, filtration, etc.). Upon contacting the 241 Am- 14 CNOM mobile complexes with Boom Clay, the major part of Am becomes almost instantaneously dissociated and immobilised, while only a small fraction persists as “stabilised complex” which migrates along with the mobile NOM. By increasing the travel time in the clay, the recovery of these complexes was observed to decrease. This decrease could be fitted to a first order kinetic model with a rate of 8 × 10 −8 s −1 indicating a slow dissociation of these “stabilised” mobile complexes.