伊盟地区人工林中主要造林树种以杨树为主。特别是在黄河冲积平原上,因杨树比其它树种生长迅速,所以无论用材林或防护林,都以杨树为主。但在不同立地条件下,初植密度和成材密度多大合适,向来没有确定下一个有科学依据的指标。五十年代,搬用苏联经验,初植密度采取每亩666株的高密度,而且成活后没有做到适时地抚育间伐,以后形成“小老头树”为多。到了六十、七十年代,人们逐步觉得初植密度过大,不便机械作业,且生长不良,也浪费种苗。所以有些地方将初植密度改为:1×2米、 The main afforestation species in the plantation of the Iran-EU alliance are poplar. Especially in the alluvial plain of the Yellow River, because poplars are growing more rapidly than other species, no matter using timber forests or shelterbelts, poplar is the mainstay. However, under different site conditions, the initial planting density and the appropriate density of the living material have never been set for the next scientifically based indicator. In the 1950s, with the experience of the Soviet Union, the planting density was 666 high-density per acre. After planting, the density was not raised in a timely manner and “small old trees” were formed afterwards. By the sixties and seventies, people gradually felt that planting density was too large, inconvenience of mechanical work, and poor growth, but also a waste of seedlings. So in some places will be planted density to: 1 × 2 meters,