青藏高原东北边缘高寒草甸植物种群生态位特征对牦牛放牧的响应

在甘肃天祝县境内的青藏高原高寒草甸牦牛牧区设置不同强度放牧小区,采用野外样方调查法研究了放牧对青藏高原高寒草甸植物组成、种重要值和种群生态位特征的影响。结果表明,青藏高原高寒草甸随放牧强度增大植物种数逐渐减少,其中紫花针茅、西藏香青、高山韭等种类在重度放牧条件下消失。在中度条件下,优势种线叶嵩草的重要值最高;另一优势种珠芽蓼的重要值则是先增加后降低再升高,以轻度放牧条件下最高。在3个放牧强度条件下,珠芽蓼和线叶嵩草的生态位宽度均位居所有种群前两位,并随着放牧强度增加二者的生态位宽度呈增大趋势,在重度放牧条件下二者生态位宽度相等。3个放牧强度下,优势种珠芽蓼和线叶嵩草与各种群间的生态位重叠系数不尽相同,封育或者轻度放牧条件下,珠芽蓼是种群间竞争较强的一方,但当放牧强度达到中度及以上时,珠芽蓼则退出种群间竞争强度激烈的局面;线叶嵩草是重度放牧下,种群间竞争强度最大的一方。说明放牧强度对青藏高寒草甸植物群落植物物种组成、重要值、生态位宽度和生态位重叠值均产生一定的影响,中度放牧强度是珠芽蓼和线叶嵩草的适宜放牧强度。运用“生态位理论”分析青藏高原高寒草甸植物群落生态特征,其结果与“中度干扰理论”相吻合,中度放牧是青藏高原高寒草甸优势种适宜的放牧强度。

Influence of yak grazing on plant niche characteristics in alpine meadow communities at the northeastern edge of the Qinghai-Tibetan Plateau

The grazing intensity changes the plant composition of alpine meadow. A field survey was carried out to determine the effect of grazing intensities on plant niche characteristics of alpine meadow communities in the Qinghai-Tibet Plateau. This study showed that the number of plant species appearing in plots reduced as the grazing intensity increased, and Anaphalis tibetica, Stipa purpurea and Allium sikkimense disappeared when grazing intensity exceeded 1.25 yak/ha. The numbers of unpalatable plants increased when the grazing intensity in plots was over 1.00 yak/ha. With increasing grazing intensity, the importance value of Kobresia capillifolia, a dominant species, initially increased and then decreased, peaking at 1.00 yak/ha grazing intensity, and the importance value of Polygonum viviparum, another dominant species peaked at 0.75 yak/ha grazing intensity. The niche breadth of K. capillifolia and P. viviparum was greater than that of other species in alpine meadow communities differing in grazing intensity and increased as the grazing intensity increased. The plants with the biggest niche overlap with K. capillifolia and P. viviparum were different. P. viviparum was one of two populations which had a bigger coefficient of niche overlap at 0 and 0.75 yak/ha grazing intensity, however, P. viviparum did not appear in the populations which had the biggest coefficient of niche overlap when the grazing intensity was over 0.75 yak/ha. K. capillifolia was one of two populations which had the biggest coefficient of niche overlap at 1.25 yak/ha grazing intensity. These results suggest that the grazing intensity changed the plant composition, species importance values, niche breadth and niche overlap of alpine meadow communities, and that a grazing intensity of 1.00 yak/ha was advantageous to the dominant species, P. viviparum and K. capillifolia, in alpine meadow at the northeastern edge of the Qinghai-Tibetan Plateau.