MAPPING AND QUANTIFYING POST-FIRE CARBON BUDGET IN AMAZONIA

全球气候变化和热带雨林的大规模丧失可能是当代最紧迫的环境问题。一些全球环流模型表明，亚马逊地区可能容易受到极端干旱的影响。如果亚马逊地区的干旱频率增加，火灾向森林的渗漏很可能成为森林转型的主要动因。这一过程通过影响植被结构、改变碳库和碳通量、引起对大气的反馈，对全球碳循环产生重要影响，但到目前为止，这种影响的量化程度很低。缺乏关于这些过程的系统信息(空间和时间)是在估计这一碳源的规模以及随后维持亚马逊森林生物群及其生态系统功能时的一个严重限制。因此，我在这项研究中的主要目的是将来自多时相卫星图像的信息与关于净生态系统生产力(NEP)组成过程的大量现场数据相结合，以：(1)生成巴西亚马逊地区受火灾影响的森林的第一张地图；(2)量化不同时间尺度、不同火灾频率和强度下从森林小室排放、吸收和转移的碳量；(3)计算考虑森林火灾影响的亚马逊森林的碳收支，并了解这种变化是如何受气候和森林砍伐率控制的；以及(4)了解森林火灾导致的碳平衡在时间和空间上的变化。为了实现这一提议的目标，第一步将是分析多时相卫星图像，以绘制受火灾影响的森林伤痕图，并量化该地区火灾的频率和强度。生物量地图将被用来识别亚马逊地区的不同森林类别。最后，将这些地图合并成一个单一的分层地图。这将表征该区域火灾损害的空间变异性。这张地图将成为确定将在实地进行详细调查的区域的基础，并将在稍后阶段用于将现场数据外推到整个亚马逊地区。第二步将解决不同火灾频率和强度对碳收支的影响。这将涉及对现有实地数据的汇编，以及在关键现场，直接测量碳平衡或NEP的组成过程，NEP是植被通过光合作用吸收的二氧化碳与生态系统通过呼吸过程释放的二氧化碳之间的差值。这些测量将提供关于在不同时间尺度上排放、吸收和在森林隔间排放、吸收和移动的碳量的详细信息。一旦分析了来自不同来源的数据，合乎逻辑的下一步是整合数据集，以便了解受火灾影响地区净环境保护的组成部分进程在整个亚马逊地区的年度变化。将初步测试两种主要办法：(1)区域平均法，其中可将净初级生产力的平均值与每个火灾类别相关联；(2)决策树方法，可通过结合关于火灾类别的信息以及非净初级生产力及其组成部分过程与降雨量、生物量和森林类型之间的经验校准关系来实施。在这个阶段，考虑到森林火灾的影响，所有信息都将可用于计算亚马逊森林的碳收支。这项工作的最终目标是得出近年来受火灾影响的林地碳吸收、释放和净平衡的年度空间显式数值，量化决定这一净碳平衡的组成过程的相对影响，并了解气候变化和人类活动如何通过砍伐森林影响其空间和时间格局。

Global climate change and the large-scale loss of the tropical forests are probably the most urgent of contemporary environmental problems. Some global circulation models suggest that Amazonia may be vulnerable to extreme drying. In the event of increased drought frequency in the Amazon region, the leakage of fires into forests is likely to be the major agent of forest transformation. This process has an important influence on the global carbon cycling by affecting vegetation structure, changing carbon pools and fluxes, and causing feedbacks to the atmosphere, but it is thus far poorly quantified. The lack of systematic information (spatial and temporal) on these processes is a critical limitation when estimating the magnitude of this carbon source and consequent maintenance of the Amazon forest biome and its ecosystem function. Hence, my main research aim in this fellowship is to combine information from multi-temporal satellite images with extensive field data on the component processes of the net ecosystem productivity (NEP) to: (1) Generate the first map of the fire-affected forests in the Brazilian Amazon; (2) quantify the amount of carbon being emitted, absorbed and moved from and among forest compartments at different time-scales and at different fire frequency and intensity; (3) calculate the carbon budget of Amazonian forests taking into account the effect of forest fires, and understand how this variation is controlled by climate and deforestation rates; and (4) understand how the carbon balance varies temporally and spatially because of forest fires. To achieve the aims of this proposal, the first step will be to analyze multi-temporal satellite images to map the scars of forests affected by fire and quantify the frequency and intensity of fire in this areas. A biomass map will be used to identify different forest classes in the Amazon. Finally, the maps will be merged in one single stratified map. This will characterize the spatial variability of fire damage in the region. This map will be the basis for defining the areas that will be investigate in detail in the field and will be also used in a later stage to extrapolate field data to the whole Amazon. The second step will tackle the effect of different fire frequency and intensity on carbon budget. This will involve a compilation of existing field data and in key field sites, direct measurements of the component processes of the carbon balance or NEP, which is the difference between the CO2 assimilated by the vegetation through photosynthesis and the CO2 released by the ecosystem through the respiration process. These measurements will provide detailed information on the amount of carbon being emitted, absorbed and moved from and between forest compartments at different time-scales. Once the data from the different sources have been analysed, the logical next step is to integrate the datasets in order to understand the annual Amazon-wide variation of the component processes of NEP in the fire-affected areas. Two main approaches will be tested initially: (1) a zonal average method, where, an average value of NEP can be associated to each fire class; and (2) a decision tree method, that can be implemented by combining information about the fire classes and empirically-calibrated relationships between NEP and its component processes with rainfall, biomass and forest type. At this stage all the information will be available for calculating the carbon budget of Amazonian forests, taking into account the effect of forest fires. The ultimate goal of this work is to arrive at annual spatially explicit values of uptake, release and the net balance of carbon in fire-affected forest sites in recent years, to quantify the relative influences of the component processes that determine this net carbon balance and to understand how climate variation and human activities through deforestation, affects its spatial and temporal patterns.