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Hundreds of studies have evaluated the dynamics of plant invasions and their impacts on native plant communities and ecosystem functions, but most are limited in duration to only one or a few years. As such, we have a poor understanding of how invader dynamics and impacts change over time., This special feature presents six studies that use literature reviews, field studies and experiments to examine long-term patterns in invader effects on species, communities and ecosystems. All studies in the special feature focus on data collected over multiple years and two studies provide data that cover multiple decades., One study provides a review and framework for understanding how invaders impact plant-mycorrhiza mutualisms and two studies focus on long-term ecosystem changes in response to invasion and fire. The next two studies examine how invaders respond to successional change and climate conditions over time, and the final study shows that invaders can shift selection regimes and the evolutionary trajectory of native plant populations., Synthesis. Articles in this special feature demonstrate changes in the dynamics of invasive plant populations and their community and ecosystem impacts over time. Together they illustrate that findings from a snapshot in time may poorly describe years-long outcomes of invasions, and they highlight the need for long-term studies of biological invasions. [ABSTRACT FROM AUTHOR]

This paper introduces a set of four collaborative papers exploring temporal heterogeneity in the analysis of African land use over a decadal time period, from 10 to 50 years, in the second half of the twentieth century. The four cases were chosen amongst the seven teams of anthropologists, human geographers and remote sensing specialists who had carried out long-term research and who met to discuss their findings at a workshop in 2003. All seven teams’ work and the collective discussion—on Casamance (Senegal), Brong Ahafo (Ghana), Southern Niger/Northern Cote d’Ivoire, Oyo State (Nigeria), Maasai Mara (Kenya and Tanzania), Gwembe (Zambia), and Malawi—inform this introduction. We identify several temporal processes in all the cases, each operating on its own temporal frame: population growth and, above all, mobility; livelihood change through crop and occupational change; tenure ambiguity; powerful though “punctuated” interventions by state policy; and climate change. Conceptual and methodological implications are disussed. [ABSTRACT FROM AUTHOR]

This volume gathers contributions that share the same double concern: to focus on teaching situations in classrooms, especially the work of the teacher, and to be strongly anchored in original theoretical frameworks allowing to take the classroom situation as unit of analysis. The contributions are not a representative sample of all research sharing this focus worldwide. The theoretical frameworks are grounded mainly (but not solely) in the theory of didactic situations (Brousseau, 1997) and the anthropological theory of didactics (Chevallard, 1992, 1999). There are 11 articles altogether, 9 of which present research works within the chosen theme and focus. The other two are commentary papers offering a reflection on studies of classroom situations from the point of view of other theoretical viewpoints. [ABSTRACT FROM AUTHOR]

River Atna is situated in south-eastern Norway and stretches from approx. 1400 m a.s.l. in the Rondane Mountains, through Lake Atnsjøen, at 701 m a.s.l.; to the confluence with River Glomma at 338 m a.s.l. The catchment area is 1323 km2, oligotrophic and very susceptible to acid precipitation. The river water is very poor in nutrients and ions, and pH varies from 5.0 to 7.2. Samples were taken each year from 1987 to 2002 at three to five localities from 1280 to 380 m a.s.l. Insect larvae were collected by Surber sampling and by kick sampling. Malaise traps were used to collect adults of Plecoptera, Trichoptera, Chironomidae and Limoniidae. A total of 16 taxa of Ephemeroptera, 24 taxa of Plecoptera, 39 taxa of Trichoptera, 125 taxa of Chironomidae and 52 taxa of Limoniidae, were identified. Our results from Atna provide some support for a zonation of the river based on zoobenthos. The occurrence and abundance of functional groups among the Plecoptera, Trichoptera, and Chironomidae are discussed in relation to the River Continuum Concept (RCC). Our conclusion is that grazers dominate in the zoobenthos in streams in the treeless alpine region in Norway. Natural lakes, which occur in most watercourses in Norway, appear to cause a disturbance in relation to the original RCC concept, as the zoobenthos community in and below the lake outlet is dominated by collectors (filter feeders). The pattern found in the Atna watercourse is probably a general pattern for a northern watercourse in the Holarctic, where the glacial periods created lakes in most watercourses. The results of the long term sampling in Atna are discussed in relation to the practicalities and the cost-benefit of zoobenthos in efficient bio-monitoring in rivers. [ABSTRACT FROM AUTHOR]