ABSTRACT

The African woodlands known as miombo are one of the world’s largest currently relatively unexploited, but potentially arable, land resources. Miombo landscapes one of the top contemporary locations of conversion of dry forests to crop agriculture. This study investigates the net effect on climate forcing that results from different types of land use change in miombo, taking into account the multiple mechanisms through which the land interacts with the climate system, locally and globally. It finds that when miombo is converted tointensively cultivated commercial crops, the landscape-averaged 30-year net greenhouse gas forcing relative to intact woodlands is 309gCO₂e m^-2 y^-1, of which net emission of carbon dioxide amount to 66%, non-CO₂ greenhouse gas effects to 33%, plus unquantified contributions from ozone precursors and aerosols. We find that net brightening of the land surface resulting from clearing the woodlands generates a cooling effect larger than the greenhouse gas forcing (-1139gCO₂e m^-2 y^-1). Greenhouse gas forcings resulting from transformation to extensive subsistence agriculture that are 78% lower than those from the intensive commercial agriculture path, and 40% lower if a transformation which sets out to mimic ecological processes in the miombo landscape is undertaken. Once the effect of surface brightening is included, then the total forcing for extensive subsistence agriculture is -834gCO₂e m^-2 y^-1 , about the same as intensive commercial, and eco-agriculture is -102gCO₂e m^-2 y^-1 . Taking into account the account the larger areas required for to achieve the same production, intensive commercial agriculture is the more climate-protective option.Keywords: greenhouse gas, net radiation, deforestation.

摘要

被称为miombo的非洲林地  是世界上最大的土地，目前尚未被开发，但潜在的耕地资源之一。米翁布（ M iombo） 风景秀丽，是干燥森林转变为农作物的当代最佳地点之一。这项研究调查了米诺姆邦不同类型的土地利用变化对气候强迫的净影响 ，同时考虑了土地在本地和全球范围内与气候系统相互作用的多种机制。研究发现，将 miombo 转换为精耕细作的商业作物后，相对于完整林地，景观平均30年净温室气体强迫为309gCO ₂ e m ^-2  y^-1，其中二氧化碳的净排放量达到66％，非CO ₂ 温室气体排放量达到33％，加上臭氧前体和浮质的未量化贡献。我们发现，清理林地导致土地表面的净增白产生的冷却效果大于温室气体强迫（-1139gCO ₂ e m ^-2  y ^-1）。转变为粗养型农业所产生的温室气体强迫，比密集商业化农业途径的温室气体强迫要低78％，如果拟模仿密博的生态过程而进行的温室气体强迫则要低40％  进行景观。一旦包括表面增白的影响，那么广泛的自给性农业的总强迫为-834gCO ₂ e m ^-2  y ^-1  ，与集约商业化的大致相同，而生态农业的总强迫为-102gCO ₂ e m ^-2  y ^-1  。考虑到实现同一生产所需的更大面积，集约化商业农业是更具气候保护性的选择。关键词：温室气体，净辐射，森林砍伐。