Relation between growth of high-yield poplar and density and planting composition in Keerqin sandy land

The relationships between high-yield forest densities, planting composition and the average D.B.H, height, canopy width, tree volume and forest volumes as well as changes with growth of stand of No.41 Baicheng poplar at the natural rainfall condition were studied in Keerqin sandy land of dry sub-humid. The results show that planting density has no effect on the growth at age of 1~5 years. The forest volumes per hectare increase with the density. After 6 years of planting, the effects of density on tree growth show gradually. The D.B.H. and tree volume increase faster for the low-density stands than that for the high-density stands, with the increase of the stand's age. After 11 years, this effect towards stable. The forest volume (153.39m³/hm²) is greatest at a density of 825 trees/hm², and that at 540 trees/hm² is greater than at 420 trees/hm², and the volume (35.18m³/hm²) is least at 1 215 trees/hm². The proportion of stems, branches and foliages are optimum at 400-1 000 trees/hm². The trees in rows in the forest edge become dominant. The D.B.H., volume and volume increment of dominant trees grow faster than those of uniform crop's in the forest at the same density. The roots of dominant trees absorbed more water because higher stand growth rate of forest belt mainly resulted from a major water use zone and a 1a-leral zone supplied by outer soil areas with higher moisture content.