Kauffman J Boone, Hughes R Flint, Heider Chris
Institute of Pacific Islands Forestry, USDA Forest Service, Pacific Southwest Research Station, 60 Nowelo Street, Hilo, Hawaii 96720, USA.
Ecol Appl. 2009 Jul;19(5):1211-22. doi: 10.1890/08-1696.1.
Current rates of deforestation and the resulting C emissions in the tropics exceed those of secondary forest regrowth and C sequestration. Changing land-use strategies that would maintain standing forests may be among the least expensive of climate change mitigation options. Further, secondary tropical forests have been suggested to have great value for their potential to sequester atmospheric C. These options require an understanding of and capability to quantify C dynamics at landscape scales. Because of the diversity of physical and biotic features of tropical forests as well as approaches and intensities of land uses within the neotropics, there are tremendous differences in the capacity of different landscapes to store and sequester C. Major gaps in our current knowledge include quantification of C pools, rates and patterns of biomass loss following land-cover change, and quantification of the C storage potential of secondary forests following abandonment. In this paper we present a synthesis and further analyses from recent studies that describe C pools, patterns of C decline associated with land use, and rates of C accumulation following secondary-forest establishment--all information necessary for climate-change mitigation options. Ecosystem C pools of Neotropical primary forests minimally range from approximately 141 to 571 Mg/ha, demonstrating tremendous differences in the capacity of different forests to store C. Most of the losses in C and nutrient pools associated with conversion occur when fires are set to remove the slashed forest to prepare sites for crop or pasture establishment. Fires burning slashed primary forests have been found to result in C losses of 62-80% of prefire aboveground pools in dry (deciduous) forest landscapes and 29-57% in wet (evergreen) forest landscapes. Carbon emissions equivalent to the aboveground primary-forest pool arise from repeated fires occurring in the first 4 to 10 years following conversion. Feedbacks of climate change, land-cover change, and increasing habitat fragmentation may result in increases of both the area burned and the total quantity of biomass consumed per unit area by fire. These effects may well limit the capacity for future tropical forests to sequester C and nutrients.
目前热带地区的森林砍伐率以及由此产生的碳排放超过了次生林再生和碳固存的速率。改变土地利用策略以维持现存森林可能是成本最低的气候变化缓解方案之一。此外，有人认为次生热带森林因其固存大气中碳的潜力而具有巨大价值。这些方案需要了解并具备在景观尺度上量化碳动态的能力。由于热带森林物理和生物特征的多样性以及新热带地区土地利用的方式和强度不同，不同景观储存和固碳的能力存在巨大差异。我们目前知识的主要空白包括碳库的量化、土地覆盖变化后生物量损失的速率和模式，以及弃耕后次生林的碳储存潜力的量化。在本文中，我们对近期研究进行了综合和进一步分析，这些研究描述了碳库、与土地利用相关的碳下降模式以及次生林建立后的碳积累速率——所有这些都是气候变化缓解方案所需的信息。新热带原始森林的生态系统碳库最低约为141至571 Mg/公顷，这表明不同森林储存碳的能力存在巨大差异。与森林转变相关的碳和养分库的大部分损失发生在为开垦农田或牧场而焚烧砍伐后的森林以准备土地之时。据发现，在干燥（落叶）森林景观中，焚烧砍伐后的原始森林会导致碳损失量达到火灾前地上碳库的62 - 80%，在湿润（常绿）森林景观中为29 - 57%。与地上原始森林碳库等量的碳排放源于转变后的头4至10年反复发生的火灾。气候变化、土地覆盖变化以及栖息地破碎化加剧之间的反馈作用可能导致火烧面积增加以及单位面积火灾消耗的生物量总量增加。这些影响很可能会限制未来热带森林固存碳和养分的能力。
