Quantifying postglacial climate and vegetation dynamics of the foreststeppe ecotone in northern Patagonia, Argentina

植被对平均气候条件和极端气候条件都有反应，因此，过去植被的变化是过去气候变化的一个很好的指标。虽然北方半球存在足够的基于花粉的定量气候重建，以提供大陆尺度的模式，但南半球，特别是南美洲的调查很少。生态过渡带区域，例如巴塔哥尼亚2000公里长的长林草原生态过渡带，对气候变化特别敏感，尽管火灾和其他反馈机制可能会延迟植被对气候变化的反应。因此，研究植被组成沿着气候梯度的空间以及通过时间是重要的，产生一个四维的理解的气候和植被动态，这将使气候的影响，从植被内部过程和火灾反馈。拟议的研究将侧重于阿根廷南部-38.7和-39.6之间的森林草原交错带。该地区在不同海拔高度有丰富的中小型湖泊，这将提供现代花粉样本，用于a）构建气候转换函数，和B）获得代表性因子，限制物种差异花粉产生的偏差。传递函数的气候变量将通过监测采集现代花粉样本的湖泊周围的相关参数（土壤湿度和温度）来获得。这种新的方法是必要的，因为研究区域在短距离内包含强烈的气候梯度，并将提供有关这些参数的平均值和变化的信息。将对穿过生态交错带的三个地点的湖泊沉积物岩芯进行化石花粉和木炭分析：一个岩芯来自潮湿一侧，第二个岩芯来自中间位置，第三个岩芯来自梯度的干燥端。前两个已经有了，并进行了放射性碳年代测定。选择第三个地点的另一个目的是获取晚冰期沉积物，以探索冰消期间的变化。初步的花粉数据表明，在6000年前，生态交错带发生了几次逐渐的变化和强烈的转变。这种转变和其他变化的程度可能被掩盖，由于过度的Nothofagus花粉。花粉传播和沉积的代表性因素和模型的应用将有助于量化的程度和动态的这种和其他情况下的冰后期植被变化。植被动态的详细重建将用于评估这些地点的定量气候重建。此外，这一信息将增加对生态区植被动态的了解，这将支持和促进该地区国家公园的保护战略。

Vegetation responds to both average climatic conditions and extremes and changes in past vegetation thus make a good indicator for past climate changes. While sufficient pollen based quantitative climate reconstructions exist for the northern hemisphere to provide continental scale patterns, investigations are rare for the southern hemisphere, in particular South America. Ecotonal regions, e.g. the 2000 km long forest steppe ecotone in Patagonia, are particularly sensitive to climate change, although fire and other feedback mechanisms may delay responses of the vegetation to climate change. Studying the vegetation composition along climate gradients in space as well as through time is therefore important to yield a four dimensional understanding of the climate and vegetation dynamics, which will allow the influence of climate to be disentangled from vegetation internal processes and fire feedback. The proposed study will focus on the forest steppe ecotone in Argentina between -38.7 and -39.6 South. This region is rich in small to medium sized lakes at different elevations, which will provide modern pollen samples to be used a) in the construction of climate transfer functions, and b) to obtain representation factors which limit biases from differential pollen production of species. Climate variables for the transfer functions will be obtained by monitoring the relevant parameters (soil moisture and temperature) around the lakes from which modern pollen samples are collected. This novel approach is necessary as the study region contains strong climate gradients over short distances, and will provide information about the mean and variation in these parameters. Fossil pollen and charcoal will be analysed from lake sediment cores of three sites crossing the ecotone: one core from the moist side, a second from an intermediate location and a third one from the dry end of the gradient. The first two are already available and radiocarbon dated. The selection of the third site has the additional objective of obtaining Lateglacial sediments to explore the changes during deglaciation. Preliminary pollen data indicate several gradual changes as well as a strong shift in the ecotone around 6000 years ago. The extent of this shift and other changes is potentially masked due to the overrepresentation of Nothofagus pollen. The application of representation factors and models of pollen dispersal and deposition will help to quantify the extent and dynamics of this and other cases of postglacial vegetation change. The detailed reconstruction of the vegetation dynamics will be used to evaluate the quantitative climate reconstruction from the sites. In addition, this information will increase the understanding of ecotonal vegetation dynamics which will support and contribute conservational strategies for the National Parks of the region.