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情况都有反应，过去植被的变化因此是过去气候变化的良好指标。虽然北半球已经有足够的基于花粉的定量气候重建来提供大陆尺度的模式，但对南半球，特别是南美洲的研究很少。交错带地区，例如巴塔哥尼亚2000公里长的森林草原交错带，对气候变化特别敏感，尽管火灾和其他反馈机制可能会推迟植被对气候变化的反应。因此，研究植被在空间和时间上沿气候梯度的组成对于对气候和植被动态有一个四维的了解，这将使气候的影响从植被内部过程和火灾反馈中解脱出来。拟议的研究将集中在阿根廷南部-38.7至-39.6之间的森林草原交错带。该地区盛产不同海拔的中小型湖泊，这将提供现代花粉样本，用于a)构建气候传递函数，以及b)获得限制物种不同花粉产生偏差的代表性因子。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上包含强烈的气候梯度，并将提供关于这些参数的平均值和变化的信息。将从穿过交错带的三个地点的湖泊沉积岩心中分析化石花粉和木炭：一个岩心来自湿润的一侧，第二个来自中间位置，第三个来自坡度的干燥端。前两个已经有了，放射性碳标出了日期。第三个地点的选择还有一个额外的目标，即获取类型冰川沉积物，以探索冰川消融期间的变化。初步的花粉数据表明，大约6000年前，交错带发生了几次渐进的变化和强烈的转变。由于Nothofagus花粉的过度表达，这种转变和其他变化的程度可能被掩盖了。花粉扩散和沉积的代表性因子和模型的应用将有助于量化这种和其他冰川后植被变化的程度和动态。植被动态的详细重建将被用来评估从现场进行的定量气候重建。此外，这些信息将增加对生态区植被动态的了解，这将为该地区的国家公园保护战略提供支持和贡献。

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.