Reactivation of sand drift is a common phenomenon in arid areas and needs suitable surface vegetation in association with overstorey trees for better stabilization. Regeneration and survival of Cassia angustifolia seedlings were studied in relation to different adult neighbours and soil water content with a view to developing effective surface vegetation and control of sand drift. Acacia tortilis, Prosopis juliflora and Calligonum polygonoides were the experimental adult neighbours. Observations were recorded at distances of 0–1.0 m (inner canopy [IC] zone), 1.0–1.5 m (outer canopy [OC] zone) and 1.5–2.5 m (outside the canopy [OS] zone) from the neighbours. Seeds and regenerated seedling densities were higher in the C. polygonoides plot than the other two neighbours and the control plots. The density was higher in the OC zone of the C. polygonoides and P. juliflora plots, the OS zone of the A. tortilis plot and the IC zone of the control plot. Both inter- and intraspecific competition resulted in high mortality during July–October in A. tortilis and P. juliflora plots. Seedling survival decreased in February and June, but the density, which was greater in the IC zone, was positively correlated with that in July and with the soil water content (SWC). The ultimate survival of seedlings was higher in the neighbour inclusion than control plots. The soil water content (SWC) was generally higher in the Calligonum polygonoides plot than that in the A. tortilis and P. juliflora plots. With distance from the adult neighbours, the SWC increased in the 25–50 cm and 50–75 cm and decreased in the 0–25 cm soil depth layers. Shoot height and biomass of one-year-old C. angustifolia seedlings were higher in the C. polygonoides plot than in the plots of other neighbours. A negative relative neighbour effect for most of the growth variables suggests that the adult neighbours facilitated regeneration, survival, growth and biomass of C. angustifolia seedlings. C. polygonoides was the best neighbour, with better soil water content at depth and the most positive influence on seedling growth; it is therefore a suitable planting partner for C. angustifolia in promoting the effective stabilization of dunes.

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Three radiological dispersal devices were detonated in 2012 under controlled conditions at Defence Research and Development Canada's Experimental Proving Grounds in Suffield, Alberta. Each device comprised a 35-GBq source of (140)La. The dataset obtained is used in this study to assess the MLCD, ADDAM, and RIMPUFF atmospheric dispersion models. As part one of a two-part study, this paper focuses on examining the capabilities of the above three models and evaluating how well their predictions of air concentration and ground deposition match observations from the full-scale RDD experiments.