The dynamics and carbon implications of fires in the Andes

自然生态系统中的火是生物群结构形成、生物群退化、大气污染和碳排放的主要动因。在这项提案中，我们将把注意力集中在一个潜在的重要但很少被研究的生态系统上：安第斯山脉的热带山地云雾森林(TMCFs)。在安第斯山脉，湿润的TMCFs紧挨着高度易燃的高海拔干燥草原(普纳)，那里几千年来一直遭受着反复的人为火灾，林线约为3000米。这条树线是一个生态和气候紧张的地带：一方面，气温和云层高度的上升可能会推动交错带向上移动，鼓励森林向普纳扩张。另一方面，普纳地区的干旱加剧(受气温上升和蒸散量的影响，可能还受到降雨量减少的影响)，再加上人类压力的加剧，火灾的发生和对云雾森林的渗透正在增加。有大量证据表明，这类火灾目前在安第斯TMCFs普遍存在，但由于这一研究系统的偏远，对这些火灾事件的系统研究很少。我们对卫星数据的分析表明，安第斯山脉的火灾可能正在大量增加，并呈现出神秘的五年周期。火灾增加的趋势在海拔2000米以上尤为明显，可能与水分胁迫增加有关，因为潜在蒸腾速率随着气温的上升而上升。鉴于火灾的发生越来越多，我们推测，因此越来越多的火灾正从普纳地区向周围的TCMF蔓延，这些地区正在退化为草原或灌木群落。TMCFs含有大量的碳，它们在火灾中的损失是向大气排放二氧化碳和其他燃烧化合物的潜在来源。碳储量和点火损失都与低地亚马逊雨林的碳储量和损失相当，但在山区，几乎所有的损失都来自土壤有机层。在这项提案中，我们将对安第斯林线火灾的空间和时间动态进行首次详细评估，并试图量化其对碳排放的影响。为此，我们将把重点放在秘鲁安第斯山脉南部(马努国家公园内和周围)的一个密集研究区域，在那里我们将确定火灾点火和蔓延的环境控制，量化与特定火灾有关的碳排放和恢复时间，并评估遥感数据扩大到更广泛的安第斯区域的火灾排放的潜力。我们的项目将涉及以下组成部分：1.构建详细的安第斯林线区域火灾历史和火灾地图，涵盖1990-2011年期间；2.对我们研究区域2009-2011年期间的所有火灾进行密集跟踪和评估。3.测量未燃烧和被烧毁森林的生物量和碳储量4.在燃烧前在森林中设置一些碳地，并在燃烧后对其进行访问5.进行干燥和点火实验，以确定林线上的可燃性阈值6.使用我们详细的现场数据来评估和校准基于卫星的火灾发生、范围和强度估计7.使用校准的卫星数据来估计热带安第斯山脉火灾的碳排放量

Fire in natural ecosystems is a major agent of biome structure formation, biome degradation, atmospheric pollution and carbon emission. In this proposal we will focus attention on fire dynamics on a potentially important but barely studied ecosystem: the tropical montane cloud forests (TMCFs) of the Andes. In the Andes, humid TMCFs sit immediately below highly flammable, high altitude dry grasslands (the puna) that have suffered from recurrent anthropogenic fires for millennia, with the treeline sitting at approximately 3000 m. This treeline is a zone of ecological and climatic tension: on the one hand, rising temperatures and cloud heights may have a tendency to push the ecotone upwards, encouraging forest expansion into the puna. On the other hand, increased aridity in the puna (driven by rising temperates and evapotranspiration, and possibly by reducing precipitation), coupled with intensified human pressure, is increasing fire occurrence and penetration into the cloud forest. There is plentiful evidence that such fires are now widespread in Andean TMCFs However, there have been few systematic studies of these fire events because of the remoteness of this study system. Our analysis of satellite data has shown that Andean fires may be increasing in abundance, and display a mysterious five year cycle. The tendency to increased fires is particularly marked at elevations above 2000m, and may be linked to increasing water stress as potential transpiration rates rise in response to rising temperatures. Given the increasing occurrence of fire, we conjecture than an increasing number of fires are therefore moving down from the puna region towards the surrounding TCMFs, which are being degraded into grasslands or shrub communities. TMCFs contain a large stock of carbon, and their loss through fire is a potential large source of carbon dioxide and other combustion compounds to the atmosphere. Both the carbon stock and the loss on ignition are very comparable to those from a lowland Amazonian rainforest, but in the mountains almost all of this loss comes from soil organic layers. In this proposal we will conduct the first detailed evaluation of spatial and temporal dynamics of fire at the Andean treeline, and attempt to quantify their implications for carbon emissions. We will do this by focussing on an intensive study region in the southern Peruvian Andes (in and around Manu National Park), where we will determine the environmental controls on fire ignition and spread, quantify the carbon emissions and recovery times associated with specific fires, and evaluate the potential of remote sensing data to scale up fire emissions to the wider Andean region. Our project will involve the following componets: 1. Construction of the fire detailed fire history and fire map of a region of the Andean treeline, covering the period 1990-2011; 2. Conducting intensive tracking and evaluation of all fires in our study region in the period 2009-2011. 3. Measuring the biomass and carbon stocks in unburned and burned forests 4. Installing some carbon plots in forests prior to burn, and visiting them afterwards 5. Conducting drying and ignition experiments to determine thresholds of flammability at the treeline 6. Using our detailed field data to evaluate and calibrate satellite-based estimates for fire occurrence, extent and intensity 7. Using calibrated satellite data to estimate carbon emissions from fires across the tropical Andes