Effects of planting density on the early growth traits of white poplar hybrid clones

To analyze the influence of planting density on growth properties of 5yearold hybrid clones of Populus tomentosa, effects of seven planting densities(2 500,1 667,1 111,833,625,500 and 417 trees/hm2) on the growth and yield properties were studied by completely random block experiments located in Weixian County, Hebei Province of northern China. The results indicated that, the effects of planting density on the diameter at breast height(DBH) and individual stand volume were significant at 1% level 4 years later after planting, that on height growth was remarkable at 5% level only in the first year of afforesting, and that on stand volume per area was significant every year in first 5 years. Regression analysis showed that planting density significantly correlated with DBH, individual stand volume and tree height negatively, and significantly correlated with stand volume positively. The effect of density on current annual increment was related with density and growth properties. The planting density exceeding 1 111 trees/hm2 could cause an early occurrence of maximum current annual increment and a short duration of rapid growth. Conversely, the low density could result in a late appearance of maximum current annual increment. According to the results, rapid growth period of shortrotation industrial plantation of clone S86 was first 2-4 years after planting.