基于多目标权重分析的草地适宜放牧率探讨

Studies on optimum grazing rates in grasslands based on a multi-objectives weighting analysis

依据生态系统服务的理念,首次发展了生态系统服务指数(ESI),试图通过对生态系统服务功能的综合考虑,提出科学的适宜放牧率的评价方法。本研究利用美国北达科他州立大学中部草原研究站17年长期放牧试验数据,选取植物多样性Shannon-Wiener指数、地上净初级生产力、土壤表层含水量和单位面积家畜增重4个指标,通过对不同指标分别赋予不同的权重,计算不同管理目标下ESI及其稳定性,并对单目标管理与多目标管理进行了比较研究。结果表明,对于北美混合普列里(Prairie)草地,围封不利用或建立自然保护区,虽然生态系统比较稳定,但既不能有效的提高植物多样性、初级生产力和土壤水分含量等生态功能,又没有畜产品产出;而在重牧或极重牧处理下虽然获得了较大的畜产品生产,但导致了草地生态系统的退化和较大的系统不稳定性。因此,这2种管理方式在实践中都是不可取的。应用生态系统服务指数综合考虑,认为应该权衡各项生态功能和生产功能,此时轻牧或中牧是最适宜的。因此,ESI的建立避免了单项指标的评价偏差,使得适宜放牧率的确定更加合理。

Based on ecosystem services theory, an ecosystem services index （ESI） is proposed to ascertain the optimum grazing rate. This paper used 17 years data from the Central Grasslands Research Extension Center, North Dakota State University, USA, including the plant biodiversity （PB） Shannon- Wiener index, aboveground net primary productivity （ANPP）, soil water （SW）, and total beef gain per unit （TBG）. Different weightings were given to different indexes and the ESI and CV were calculated to compare single-objective and multi-objectives. In the prairies of North America, ungrazed or nature reserves were helpful in maintaining the stability of ecosystems, but had low PB, ANPP, SW and TBG. High or extreme grazing intensity resulted in bigger beef gains per unit, but led to degradation of grasslands and lower stability. Thus, neither of these indexes gave optimum grazing rates in practice. The ecosystem services index showed that a light or moderate grazing rate would give a better balance between ecosystem function and production. Thus the construction of the ESI avoids the problems of single indexes and results in a more balanced grazing rate.