The dynamics and carbon implications of fires in the Andes

在自然生态系统中，火灾是生物群系结构形成、生物群系退化、大气污染和碳排放的主要动因。在本提案中，我们将把注意力集中在一个潜在重要但几乎没有研究过的生态系统的火灾动力学上：安第斯山脉的热带山地云雾林（tmcf）。在安第斯山脉，潮湿的tmcf位于高度易燃的高海拔干燥草原（puna）下方，这些草原数千年来一直遭受着周期性的人为火灾，树木线位于大约3000米的地方。这条树线是一个生态和气候紧张的区域：一方面，不断上升的温度和云层高度可能有将过渡带向上推的趋势，鼓励森林向普纳地区扩张。另一方面，普纳高原的干旱加剧（由气温上升和蒸散作用造成，也可能由降水减少造成），加上人类压力的加剧，正在增加火灾的发生和对云雾林的渗透。有大量证据表明，这种火灾现在在安第斯山脉的tmcf中很普遍。然而，由于该研究系统的偏远性，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，安第斯山脉的火灾数量可能正在增加，并呈现出一个神秘的五年周期。在海拔2000米以上的地区，火灾增加的趋势尤为明显，这可能与随着温度上升，潜在蒸腾速率上升而增加的水资源压力有关。鉴于火灾发生率的增加，我们推测越来越多的火灾正从普纳地区向下移动到周围的TCMFs，这些TCMFs正在退化为草原或灌木群落。tmcf含有大量的碳，它们在火灾中的损失是二氧化碳和其他燃烧化合物进入大气的一个潜在的大来源。碳储量和燃烧损失与亚马逊低地雨林的碳储量和燃烧损失非常相似，但在山区，几乎所有的碳损失都来自土壤有机层。在本提案中，我们将对安第斯树线的火灾时空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（马努国家公园及其周边地区）的一个密集研究区域，在那里我们将确定对火灾着火和蔓延的环境控制，量化与特定火灾相关的碳排放和恢复时间，并评估遥感数据在更广泛的安第斯地区扩大火灾排放的潜力。我们的项目将包括以下几个部分：构建详细的火灾历史和安第斯树线区域的火灾地图，涵盖1990-2011年期间；2. 对2009-2011年研究区所有火灾进行了深入的跟踪和评估。3. 测量未燃烧和燃烧森林的生物量和碳储量在森林燃烧前设置一些碳块，并在燃烧后访问它们。进行干燥和点火实验，以确定树线处的可燃性阈值。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。利用校准过的卫星数据来估计热带安第斯山脉大火的碳排放量

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