Collaborative Research: Climatic and biotic controls on Late Quaternary erosion in the Oregon Coast Range

塑造地貌并构成自然灾害的地貌过程随气候波动而变化，气候波动是地球过去几百万年历史的特征。虽然一些气候驱动的侵蚀过程，如冰川，留下了深刻的地形印记，但其他的更难破译。例如，植被的变化应该会影响山体滑坡的频率和规模，以及山坡上土壤生产和运输的活力，但关于景观对第四纪晚期植被变化的响应的信息很少。通过结合俄勒冈海岸一个滑坡堰塞湖的古侵蚀和古生态记录，这项研究将记录晚第四纪植被变化如何转化为景观变化。这项研究将对之前公布的一项古环境记录进行扩展和补充，该记录表明，在过去的4万多年里，研究区域的森林结构和组成发生了巨大变化。通过使用来自额外湖泊沉积物岩心的宇宙源放射性核素分析古侵蚀速率，这项研究将确定树木密度和大小的增加是否倾向于增加或减少沉积物输送和侵蚀的速率。尽管树木和林下植被对固定土壤和抑制人类时间尺度的侵蚀很重要，但生物扰动被认为是随着时间的推移而产生景观变化的主要驱动力。因此，以目前的知识基础很难预测从草地为主的公园森林到封闭的针叶林的净地貌效应。该项目的成果将解决气候和地貌过程之间的一级联系，并测试新出现的数字模型，这些模型评估地貌如何随着千年尺度的气候和植被变化而演变。研究项目试图记录和量化过去40,000年来气候和植被的变化如何影响陡峭的森林景观的侵蚀速度。预期结果对于预测未来气候变化将如何影响景观动态以及解释人类引起的变化，如与木材采伐相关的变化，具有重要意义。尽管存在许多数值模型来预测气候变化对景观的调整，但人们对控制方程知之甚少，尤其是植被的作用需要显著的量化进步。通过利用保存在湖泊中的山区环境的详细沉积记录，结果将揭示生态系统和景观可能是如何共同进化形成目前的地形的。研究结果还应该揭示，在近代地质史上，是否发生过因气候或植被变化而发生的“事件”或地表快速变化时期。

Geomorphic processes that sculpt landscapes and constitute natural hazards vary with climatic fluctuations that have characterized the last several million years of Earth history. While some climate-driven erosional processes, such as glaciers, leave a profound topographic imprint, others are more difficult to decipher. Changes in vegetation, for example, should affect the frequency and magnitude of landslides and the vigor of soil production and transport on hillslopes, yet there is sparse information regarding landscape response to late Quaternary variations in vegetation. By coupling records of paleo-erosion and paleo-ecology from a landslide-dammed lake in the Oregon Coast Range, this research will document how late Quaternary vegetation changes translated into landscape modification. The study will extend and augment a previously published paleoenvironmental record showing that the structure and composition of forests in the study area have changed dramatically over the last 40,000+ years. By analyzing paleo-erosion rates using cosmogenic radionuclides from additional lake sediment cores, the study will determine whether increases in the density and size of trees tend to increase or decrease rates of sediment transport and erosion. Although trees and understory vegetation are important for anchoring soil and suppressing erosion over human timescales, bioturbation is thought to be a major driver of landscape change when integrated through time. As such, the net geomorphic effect of a change from meadow-dominated, parkland forests to closed, coniferous forests is difficult to predict with the current knowledge base. The project results will address first-order linkages between climate and geomorphic processes and test emerging numerical models that assess how landscapes evolve in response to millenial-scale climate and vegetation changes.The research project seeks to document and quantify how changes in climate and vegetation over the last 40,000 years have affected rates of erosion in a steep, forested landscape. The anticipated outcomes are important for predicting how future climate change will influence landscape dynamics as well as interpreting human-induced changes, such as those associated with timber harvesting. Although numerous numerical models exist to predict landscape adjustment to climate change, the governing equations are poorly understood and in particular, the role of vegetation requires significant quantitative advancement. By exploiting a detailed sedimentary record preserved in a lake from a mountainous environment, the results will reveal how ecosystems and landscapes may have co-evolved to generate the current terrain. The results should also reveal whether 'events' or periods of rapid surface change have occurred in recent geological history in response to climate or vegetation change.