农牧交错带县域农牧系统对气候波动的响应机制

农牧系统过程对气候波动的响应机制既是建立农牧耦合系统的主要科学问题又是农牧交错带可持续发展的关键问题之一。以盐池县1954—2013年气候和农牧系统过程为例,运用变异系数、逐步回归方法和经验模态分解法,分析了气候、农业、牧业系统12个指标的波动周期、振幅和方差贡献率,据此研究了它们之间的波动关系。结果表明:1)农牧系统受气候影响具有较大波动性。波动由强到弱依次为气候、农业、牧业,呈逐级传递的特性。三者的高频波动分量的方差贡献率依次减小,而中低频波动分量的方差依次增大。2)近60年农牧系统过程主要受经济系统驱动发生趋势性变化,同时受气候的驱动发生波动。农业在突变前受气候影响较大而突变后明显减小;同样牧业在突变前受农业影响大,突变后也明显减小。经济对农牧系统过程的影响逐渐增强。它在提高和稳定粮食总产量同时导致家畜数量特别是羊只总数的剧增,使得牧业波动加剧。3)农牧系统的波动差异、相互关联以及对气候的响应的分析表明,农牧耦合系统具有减少内部要素波动性的功能。因此,依据生态和经济规律设计具有健全正负反馈机制的农牧耦合系统是实现农牧交错带农牧业可持续发展的重要途径。

Response mechanisms of a county territory agro-pastoral system to climate fluctuations in an agro-pastoral transitional zone

The response mechanism of an agro-pastoral system to climate fluctuations is one of the major scientific challenges associated with the establishment of an agro-pastoral coupling system, as well as being a key problem related to the sustainability of an agro-pastoral transitional zone. By using stepwise regression analysis (SRA) and empirical mode decomposition method, we evaluated the dynamics of climate fluctuation and the corresponding changes in the agro-pastoral system of Yanchi County between 1954 and 2013. The range, amplitude, and variance contribution rate were analyzed for 12 indicators in the climate system, agricultural system, and animal husbandry system. Furthermore, we explored the relationships among fluctuations in climate, agriculture, and animal husbandry. The results demonstrated the presence of clear fluctuations in the agro-pastoral system, which corresponded to climate fluctuations in the past 60 years. The sequence of fluctuations ranging from strong to weak comprised the climate, agriculture, and animal husbandry systems. The amount of variance contributed by high-amplitude intrinsic mode functions (IMFs) was the highest for climate indicators, followed by agricultural indicators and animal husbandry indicators. However, the amounts of variance contributed by medial- and low-amplitude IMFs exhibited the opposite trend, increasing from climate indicators to agricultural indicators and then animal husbandry indicators. The SRA showed that the main factors contributing to the fluctuations were annual precipitation, followed by the total grain output and total number of sheep. Thus, the amplitude of the system was higher when it was more controlled by nature. Furthermore, the agriculture and animal husbandry systems generally exhibited changes due to the combined effects of economic factors and climate fluctuation during the past 60 years. Agriculture was affected the most strongly by climate before 1999 when an abrupt change occurred, but subsequently, the effects were weak. Similarly, animal husbandry was affected the most strongly by agriculture before the abrupt change point, and the effects were weaker thereafter. In addition, in recent years, both the agriculture and animal husbandry systems have been increasingly influenced by economic factors. The input of water and capital has improved and stabilized the total grain yield, thereby leading to dramatic increases and further extreme fluctuations in livestock numbers. Finally, the differences in the fluctuations, correlations, and climate response features of the agriculture and animal husbandry systems demonstrated that coupling these systems may help to reduce fluctuations in these individual systems. Therefore, it is important to design an agriculture and animal husbandry coupling system with balanced positive and negative feedback according to the rules of ecology and economics in order to achieve sustainability in the agro-pastoral transitional zone.