近几年来,在山区、丘陵区的不少地方大面积营造集中成片的落叶松、油松等针叶树的纯林,在浅山区、平原地区,大量营造杨树纯林,由于造林树种单一,面积大而集中,已经出现了一些弊病,病虫害严重,造成很大损失。危害严重的地方,林木成片死亡,危害较轻的林木,生长也明显地衰 In recent years, a large number of pure forests of conifers such as larch and pine are concentrated in many areas in the mountainous areas and hilly areas. In the shallow mountains and plain areas, a large number of pure forests of poplar are planted. Because of the single afforested tree species and large area However, some shortcomings have emerged as a result of the concentration. Pests and diseases are serious and have caused great losses. Harmful places, forest trees into pieces, less harmful to the trees, growth also significantly decline