基于改进关键场的干旱风沙草原牧区草畜平衡评价

牧区合理载畜量的确定是进行草畜平衡评价的核心工作之一,对指导牧区经济、社会和生态环境的可持续发展具有重要意义。中国西北干旱风沙草原受不合理放牧的影响,草地退化、沙化、盐碱化问题突出,为保护草原生态系统而实施的季节性间歇放牧制度使得牧区草畜供需关系进一步复杂化,牧区合理载畜量的确定缺乏有效的计算方法,草畜平衡评价的指导意义不强。该研究选取鄂托克旗牧区作为典型研究区,引入载畜量年内波动系数和草地生产力丰平枯系数2个动态参数,构建了一种基于改进关键场的牧区合理载畜量计算方法,并结合草畜平衡指数(Balance of Grassland and LivestockIndex,BGLI)对鄂托克旗牧区的草畜平衡状况进行了分析。结果表明,干旱风沙草原牧区草畜供需过程非一致性显著,牧业年度内形成了包含5个子过程的动态周期;改进关键场方法充分考虑了这一供需节律匹配关系,对传统和关键场方法进行了改进和完善,其在干旱风沙草原牧区合理载畜量计算中更具适用性,合理载畜量计算结果表明牧区各分区的冷季草场占比过高,现状年桌子山及山前平原分区、都斯图流域分区以及内流河分区的全年合理载畜量分别为8.60、53.49和27.66万羊单位;基于改进关键场方法对鄂托克旗牧区进行草畜平衡评价可知,现状年内流河分区超载最为严重,牧区各草场及全年的BGLI值均在105%左右,桌子山及山前平原分区次之,均在40%以上,而都斯图流域分区草畜平衡状况相对良好。

Evaluation of forage-livestock balance for pastoral areas in arid sandy grasslands using improved key pasture approach

Abstract: Determination of theoretical carrying capacity is one of the most essential requirements for the evaluation of forage-livestock balance in pastoral areas of Northwest China. Degradation, desertification, and salinization of arid sandy grasslands are becoming increasingly prominent for the reason of unreasonable grazing in recent years. Intermittent grazing has been implemented for the protection of fragile grassland ecosystem, leading to an imbalance between the grassland supply and livestock demand. It is highly urgent to accurately evaluate the forage-livestock balance for pastoral areas in arid sandy grassland. Taking the pastoral areas in Otog Banner as the typical study area, this study deeply analyzed the natural matching between grassland supply and livestock demand and proposed two dynamic factors reflecting the annual fluctuation of stocking capacity and the changes in grassland productivity in a wet, normal, and dry year. On the bases of those the improved key pasture approach was built. Traditional, key pasture, and improved key pasture approaches were used to calculate the theoretical carrying capacities of pastoral areas under various rainfall conditions in different water resource regions of Otog Banner. Then the forage-livestock balance in pastoral areas was evaluated using the Improved Key Pasture approach combing with the Balance of Grassland and Livestock Index (BGLI). The results show that the natural processes of grassland supply and livestock demand were significantly imbalanced in time for pastoral areas of arid sandy grasslands. A dynamic cycle included 5 sub-processes using the natural matching in annual animal husbandry. Meanwhile, the Improved Key Pasture approach was more suitable for the calculation of theoretical carrying capacity in the pastoral areas in arid sandy grasslands, compared with the Traditional and Key Pasture approaches. The theoretical carrying capacities were achieved for warm season pastures, cold season pastures, and artificial grassland. There was a downward trend of theoretical carrying capacities with the decrease of rainfall. The proportion of cold season pastures was too high to be fully utilized in all three divisions. The theoretical carrying capacities of the whole year in the three divisions of Zhuozishan Mountain, Dusitu River Watershed and Inland River Watershed were 86.0, 534.9, and 276.6 thousand sheep units in the status quo year, respectively. In the evaluation of forage-livestock balance, there was the most serious overload for Inland River Watershed division in the status quo year. The BGLIs of each grassland and the whole year were about 105% in Inland River Watershed division, then followed by that in Zhuozishan Mountain division of about 45%. In Dusitu River Watershed division, the forage-livestock balance was relatively good, but still in marginal overload states. The finding can contribute to the protection and restoration of the grassland ecosystem for better development of the regional economy and society.