河北杨(Populus hopeiensis Hu et Chow)生长快,抗逆性强,是陕北水土保持和固沙造林的主要树种。这个树种根蘖力强,群众说它是子母树,栽一株,成一片。目前,河北杨主要通过根蘖繁殖,形成块状林。横山县有块状林1万多亩,多分布在芦河和无定河河川,丘陵沟壑区和沙区也有,生长较好。1961—63年,我们调查了影响河北杨根蘖繁殖的因子,现分述如下。一、母树年龄用1年生根蘖苗造林,3年后自身产生根蘖苗,10—20年生为产生根 Populus hopeiensis Hu et Chow grew fast and was strong in stress resistance. It is the main tree species for soil and water conservation and afforestation in northern Shaanxi. This species is strong in root tillering, and the masses say it is a tree of trees and trees planted into a single piece. At present, Hebei Yang mainly reproduce by root tillering, forming massive forest. Hengshan County block forest more than 10,000 mu, mostly in the Lo River and Wudinghe River, hilly and sandy areas also have good growth. In 1961-63, we investigated the factors that affect the growth of Hebei tillering tillers, and are described as follows. First, the age of the mother tree with 1-year-old tillering afforestation, 3 years after its own production of tillering seedlings, 10-20 years to produce root