INFLUENCE OF GRAZING RATE ON POPULATION STRUCTURE OF STIPA GRANDIS
不同放牧率对大针茅种群结构的影响

The experiment on the influence of continuous grazing rates on population structure of Stipa grandis was conducted over two years. The following results were obtained. Within the certain scope of grazing rates, the tiller density per bunch increased along with the increase of grazing rate, and decreased outside the scope. The numbers of reproductive shoots and seed, and the weight of seed per unit area decreased with increased grazing rate, while the weight of 1000 seeds was highest under light and moderate grazing. There was a significant difference in tiller density among different age groups, in which the highest tiller density occurred in senior bunches; tiller density was lowest in juvenile bunches, while adult bunches showed intermediate tiller density. The light and moderate grazing rates can punctuate the adult and senior bunch tillering, and increase their tiller density. Senior bunches possessed an important position in the sexual reproduction of the population, and the number of reproductive shoots present was higher than that of adult bunches.