一、问题的提出杨树是我国平原绿化的重要树种之一。二十年来,我国林业工作者培育和引进了大量杨树新品种和无性系,并已推广试种。在华北、中原地区推广的有沙兰杨、I-214杨;在江苏、湖南、湖北和山东等部分地区推广的有I-72杨、I-69杨、I-63杨等。以上5个品种均为速生品种,深受群众欢迎。但它们也有不足之处,即造林成活率低。据调查,河北省 First, the issue put forward Poplar is one of the important tree species in the plains of our country. In the past two decades, forestry workers in our country have cultivated and introduced a large number of new poplar varieties and clones and have promoted the cultivation of seeds. In northern China and Central Plains, Poplar I-214 and poplar I-72 popularized in parts of Jiangsu, Hunan, Hubei and Shandong provinces. The above five varieties are fast-growing varieties, welcomed by the masses. But they also have some shortcomings, that is, the survival rate of afforestation is low. According to the survey, Hebei Province