MAPPING AND QUANTIFYING POST-FIRE CARBON BUDGET IN AMAZONIA

全球气候变化和热带森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，亚马逊河流域可能容易受到极端干旱的影响。如果亚马逊地区干旱频率增加，火灾蔓延到森林很可能是森林变化的主要因素。这一过程通过影响植被结构、改变碳库和碳通量以及引起对大气的反馈，对全球碳循环产生重要影响，但迄今为止，这一过程的量化程度很低。在估计这一碳源的规模以及由此产生的亚马逊森林生物群落的维持情况及其生态系统功能时，缺乏关于这些过程的系统信息（空间和时间）是一个关键的限制因素。因此，我在这个奖学金的主要研究目标是联合收割机信息从多时相卫星图像与广泛的实地数据的组成过程的净生态系统生产力（NEP）：（1）产生的第一张地图火灾影响的森林在巴西亚马逊河;（2）量化碳排放量，在不同时间尺度、不同火灾频率和强度下，林内和林内各林组间的吸收和迁移;（3）计算亚马逊森林的碳预算，考虑森林火灾的影响，并了解这种变化如何受到气候和森林砍伐率的控制;以及（4）了解碳平衡如何因森林火灾而在时间和空间上发生变化。为实现这一建议的目标，第一步将是分析多时相卫星图像，绘制受火灾影响的森林的痕迹图，并量化这一地区火灾的频率和强度。将使用生物量图来确定亚马逊地区不同的森林类别。最后，这些地图将被合并成一个单一的分层地图。这将表征该区域火灾损失的空间变异性。这张地图将是确定将在实地详细调查的地区的基础，也将在稍后阶段用于将实地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。这将涉及汇编现有的实地数据，并在关键的实地地点直接测量碳平衡或NEP的组成过程，即植被通过光合作用吸收的CO2与生态系统通过呼吸过程释放的CO2之间的差异。这些测量将提供关于在不同时间尺度上从森林分区和在森林分区之间排放、吸收和转移的碳量的详细资料。一旦对不同来源的数据进行了分析，合乎逻辑的下一步是整合数据集，以了解受火灾影响地区非紧急事件组成过程在整个亚马逊地区的年度变化。将首先测试两种主要方法：（1）区域平均法，其中，NEP的平均值可以与每个火灾类别相关联;和（2）决策树法，可以通过结合关于火灾类别的信息和NEP及其组成过程与降雨量、生物量和森林类型之间的精确校准关系来实施。在这一阶段，所有信息都将用于计算亚马逊森林的碳预算，同时考虑到森林火灾的影响。这项工作的最终目标是得出近年来受火灾影响的森林地点的碳吸收、释放和净平衡的年度空间明确值，以量化决定这种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毁林影响其空间和时间模式。

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.