藏北紫花针茅高寒草原适宜放牧率研究

通过5年的放牧试验研究了藏北紫花针茅高寒草原地上现存量和草地净初级生产力以及藏系绵羊采食量和采食率,以期能够准确制定藏北高寒草原适宜放牧率。研究结果表明,试验初期放牧强度对藏北紫花针茅高寒草地现存量的影响并不显著;随着试验后期对放牧强度增倍,草地地上现存量随放牧强度增加而减少。放牧样地地上净初级生产力在试验初期高于对照样地,但随着放牧强度和时间的增加,到2010年时对照样地净初级生产力明显高于放牧处理(P<0.05)。绵羊采食量与放牧强度间存在显著负相关(P<0.05);绵羊采食率大小顺序为:重牧>轻牧>中牧。综合分析试验结果,轻度放牧条件下,不仅草地现存量和净初级生产力最大,并且绵羊采食量也为最大,因此建议在牧草生长季内藏北紫花针茅高寒草原放牧率应低于4只/1.67 hm²为宜。

A study on optimal grazing rates in Stipa purpurea alpine grassland in Northern Tibet

Stipa purpurea alpine grassland is the most representative and important natural pasture of Northern Tibet but in recent years has suffered large-scale degradation, mainly from overgrazing. Optimization of S. purpurea alpine grassland grazing systems in Northern Tibet is a very important issue for local policy makers. Livestock feed intake is an evaluation method of grassland productivity and is one of the important tools of grassland management as it is a key factor in the grazing system. Grassland standing crops and the feed intake rate of Tibetan sheep are critical criteria for healthy and sustainable development of alpine grassland in Northern Tibet. Based on 5 years (2006-2010) of grazing in S. purpurea alpine grassland in Amdo County, Nagqu Region, Tibet Autonomous Region, the biomass of standing crops and net primary production of grassland and Tibetan sheep feed intake were studied using four grazing rates. In the first three years (2006-2008) of the experiment, the stocking rate was: 0 sheep/1.67 ha (CK), 2 sheep/1.67 ha (LG, light grazing), 3 sheep/1.67 ha (MG, moderate grazing), and 5 sheep/1.67 ha (HG, heavy grazing). In a later experiment (2009-2010), the grazing rate was doubled to 0 sheep/1.67 ha (CK), 4 sheep/1.67 ha (LG), 6 sheep/1.67 ha (MG), and 10 sheep/1.67 ha (HG). In the growing season of 6-9 months, based on the method of community investigation, the standing crops within 0.5 m×0.5 m quadrants were measured and the feed intake was calculated by the formula: Feed intake=Before grazing biomass-after grazing biomass+growth matter. There was no significant effect on standing crops of grazing intensity in the first study, but with the doubling of grazing intensity in the later experiment, the standing crops decreased with increased grazing intensity. The aboveground net primary production of the grazing area was larger than in the control pilot in 2006 but by 2010, in the control treatment it was significantly (P<0.05) larger than in the grazing treatment. The feed intake of Tibetan sheep was significantly negatively correlated with grazing intensity (P<0.05). The order of intake rate of sheep was: heavy grazing intensity>light grazing intensity>moderate grazing intensity. Comprehensive analysis of the results indicated that, in the light grazing treatment, not only was the biomass of standing crops and aboveground net primary production the largest, but also the feed intake of sheep was relatively high. We therefore consider that the optimal stocking rate of S. purpurea alpine grassland in Northern Tibet should be less than 4 sheep/1.67 ha.