Moore J L, Howden S M, McKeon G M, Carter J O, Scanlan J C
Bureau of Rural Sciences, Kingston, ACT, Australia.
Environ Int. 2001 Sep;27(2-3):147-53. doi: 10.1016/s0160-4120(01)00075-7.
This study outlines the development of an approach to evaluate the sources, sinks, and magnitudes of greenhouse gas emissions from a grazed semiarid rangeland dominated by mulga (Acacia aneura) and how these emissions may be altered by changes in management. This paper describes the modification of an existing pasture production model (GRASP) to include a gas emission component and a dynamic tree growth and population model. An exploratory study was completed to investigate the likely impact of changes in burning practices and stock management on emissions. This study indicates that there is a fundamental conflict between maintaining agricultural productivity and reducing greenhouse gas emissions on a given unit of land. Greater agricultural productivity is allied with the system being an emissions source while production declines and the system becomes a net emissions sink as mulga density increases. Effective management for sheep production results in the system acting as a net source (approximately 60-200 kg CO2 equivalents/ha/year). The magnitude of the source depends on the management strategies used to maintain the productivity of the system and is largely determined by starting density and average density of the mulga over the simulation period. Prior to European settlement, it is believed that the mulga lands were burnt almost annually. Simulations indicate that such a management approach results in the system acting as a small net sink with an average net absorption of greenhouse gases of 14 kg CO2 equivalents/ha/year through minimal growth of mulga stands. In contrast, the suppression of fire and the introduction of grazing results in thickening of mulga stands and the system can act as a significant net sink absorbing an average of 1000 kg CO2 equivalents/ha/year. Although dense mulga will render the land largely useless for grazing, land in this region is relatively inexpensive and could possibly be developed as a cost-effective carbon offset for greenhouse gas emissions elsewhere. These results also provide support for the hypothesis that changes in land management, and particularly, suppression of fire is chiefly responsible for the observed increases in mulga density over the past century.
本研究概述了一种评估以澳洲相思树（Acacia aneura）为主的半干旱放牧牧场温室气体排放源、汇及排放规模的方法的开发过程，以及这些排放如何因管理变化而改变。本文描述了对现有牧场生产模型（GRASP）的修改，以纳入气体排放成分以及动态树木生长和种群模型。完成了一项探索性研究，以调查燃烧方式和牲畜管理变化对排放的可能影响。该研究表明，在给定单位土地上维持农业生产力与减少温室气体排放之间存在根本冲突。更高的农业生产力与该系统成为排放源相关联，而随着生产下降且澳洲相思树密度增加，该系统成为净排放汇。有效的绵羊生产管理导致该系统成为净排放源（约60 - 200千克二氧化碳当量/公顷/年）。排放源的规模取决于用于维持系统生产力的管理策略，并且在很大程度上由模拟期内澳洲相思树的起始密度和平均密度决定。在欧洲人定居之前，据信澳洲相思树林地几乎每年都被焚烧。模拟表明，这种管理方式会使该系统成为一个小的净汇，通过澳洲相思树林的最小生长，温室气体的平均净吸收量为14千克二氧化碳当量/公顷/年。相比之下，抑制火灾和引入放牧会导致澳洲相思树林变厚，该系统可成为一个显著的净汇，平均吸收1000千克二氧化碳当量/公顷/年。尽管茂密的澳洲相思树会使土地基本上无法用于放牧，但该地区的土地相对便宜，并且有可能被开发成为其他地方温室气体排放的具有成本效益的碳抵消项目。这些结果也为以下假设提供了支持，即土地管理的变化，特别是火灾抑制，是过去一个世纪中观察到的澳洲相思树密度增加的主要原因。
