杨树速生丰产林项目从1999年绿色通道工程启动后,发展速度突飞猛进,大部分地块的苗木来源于上级直拨,老百姓对林木栽植管理没有系统了解,大部分地块栽植密度过大,致使林分过早郁闭,林木生长减退,特别是胸径生长迅速减退,导致成林期推迟,出材率下降。一般来说,在幼林时期,密度大一些,单位面积上树高、胸径、材积会随着密度的增加而增加,但是增加到一定程度后,随着林分密度偏大,土壤营养面积 Poplar fast-growing high-yield forest project started in 1999 after the green channel project, the rapid development of the rapid development of most of the land nursery stock from the higher direct dialing people do not have a systematic understanding of forest planting and management, planting density in most plots, resulting in forest Premature closure, the growth of trees diminished, especially rapid decline in DBH growth, leading to delayed forestation, the decline in the rate of timber. Generally speaking, in the young forest period, the density was higher and the height, DBH and volume per unit area increased with the increasing of the density. However, with the increase of the stand density, the soil nutrient area