水土流失严重的山地丘陵地区,普遍缺乏森林植被的覆被,一般土层浅薄,干旱贫瘠,恢复森林景观也存在较大的困难。其中一条重要的原因是适生树种很少。某些松、柏虽适应性强,亦能单独成林,但初期生长速度十分缓慢,保水改土效益差,且单纯林易遭病虫等灾害。据我们在四川省盐亭县调查,有较多的固氮树种生长发育良好。这些树种具体有能固氮、适应性较强、生长迅速和用途广泛等特点,是其它许多树种所不及的。采用固氮树种作为先锋树种或混交林中的伴生树种,可以加速荒山荒坡的绿化,有 Hilly areas with serious soil erosion and soil erosion generally lack the vegetation cover of forest vegetation. In general, the soil is shallow and the arid environment is barren. There are also great difficulties in restoring the forest landscape. One of the important reasons for this is that there are few suitable species for living. Some pine and cypress, although adaptable, can stand alone, but the initial growth rate is very slow, poor water and soil improvement, and simple forest vulnerable to pests and diseases. According to our survey in Yanting County, Sichuan Province, more nitrogen-fixing species grow well. Species of these species can nitrogen fixation, adaptability, rapid growth and wide range of uses, and many other species are beyond. The use of nitrogen-fixing species as pioneer tree species or mixed tree species in mixed forests can accelerate the afforestation of the barren hills and slopes, with