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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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Tecomella undulata L. (Rohida) is a common tree of traditional agroforestry systems of the northwestern dry region of India. Seedlings ofT. undulata at 1666, 833 and 416 stem ha-1 stand densities were thinned in July 1995 to maintain them at 417 (0 1 ), 278 (0 2 ) and 208 (0 3 ) stem ha-1 , respectively, to find out the optimum density with tree age. Vigna radiata (L.) Wilczek (mungbean) and Pennisetum glaucum (L.) R.Br. (pearl millet) were the intercrops. The increase in height and collar diameter between June 1995 and June 2002 was 2.6 and 3.3 fold in D 1 to 2.0 and 2.3 fold in D 3 plots, respectively. Grain and straw yield was lower under intercropping than with a sole agricultural crop. Production was significantly lower (p < 0.01) in D 1 plot. It was highest in 0 2 plot during 1995 and 1996 and in 0 3 plot during 2000 and 200 I. The trees produced a utilizable biomass of2.5 to 3.2 t ha-1 in 1996 and.3.63 to 4.08 t ha-1 in 1999. Soil water content differed significantly (p < 0.05) in deeper soil layers and was lower near the root zone than at 2 m distance and in the centre of four trees. Utilization of soil water was more when pearl millet rather than mung bean was the intercrop. Soil POrP and N0 3 -N were lower and NHrN was higher near the root zone than at 2m distance. Two hundred and seventy eight stems ha-1 was most favourable for crop production at the age of 6-7 years and 208 stem ha-1 at 10-11 years.

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