冀西北间山盆地区和冀北坝上西区,由于50至60年代杨树品种资源缺乏,在干瘠沙地、盆周山麓、浅山丘陵,或干旱草原,大都用当地仅有的小叶杨、青杨品种,采取发育阶段老的枝条,搞大面积压条造林。形成了86万亩长势衰弱,干形弯曲,红心病严重,成材困难的以“小老树”为主的劣质低产林。 为了改劣换优。从1968年开始,先后由北 Due to the lack of poplar species resources in the 1950s and 1960s, most of the poplar and poplar grasslands in the northwestern Hebei Province are mostly poplar, Qingyang varieties, take the old stage of development of branches, engage in large-scale afforestation. 86 million mu of poor and low-yielding forests dominated by “little old trees” were formed, with 86 million mu of weakening, dry-bending, serious densities and difficulties. In order to change the best. From 1968 onwards, successively from the north