一、引言我国西北各省,素以草长羊肥为畜牧业繁盛之区,惟以数千年来不断垦颂变林地、牧地为农地,因之草地面积日益缩小。草地面积愈小,草的来源愈少。于是放牧者不得不集中于小区域内放牧,而造成过度放牧的现象,将可食的牧草啮食殆尽,所存者仅少数耐食尺不善食的草类,如醉马草、糙米茅、苦豆子、艾蒿等。牲畜因饲料缺乏吃不饱,体 I. INTRODUCTION The provinces of the northwest of China are well-known for their long-run husbandry of livestock and governed sheep. However, for thousands of years, forests and animal husbandry have been reclaimed from forests and grasslands. Because of this, grassland has been shrinking. The smaller the grass area, the less the source of grass. As a result, the herders had to concentrate on grazing within a small area, resulting in overgrazing. Edible pastures were exhausted. Only a few surviving grasses, such as drunken horse, brown rice grass and bitter beans , Mugwort and so on. Livestock lack of feed due to lack of feed, body