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

塑造景观和构成自然灾害的地貌过程随着气候波动而变化，这是过去几百万年地球历史的特征。虽然一些气候驱动的侵蚀过程，如冰川，会留下深刻的地形印记，但其他的则更难破译。例如，植被的变化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，但关于景观对晚第四纪植被变化的响应的信息很少。通过对俄勒冈海岸山脉一个滑坡堰塞湖的古侵蚀和古生态记录的耦合，本研究将记录晚第四纪植被变化如何转化为景观改变。这项研究将扩展和增强先前发表的一项古环境记录，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成因放射性核素分析古侵蚀速率，该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运输和侵蚀速率。虽然树木和林下植被在人类时间尺度上对锚定土壤和抑制侵蚀很重要，但随着时间的推移，生物扰动被认为是景观变化的主要驱动力。因此，从草甸为主的公园森林到封闭的针叶林的变化的净地貌效应很难用现有的知识基础来预测。该项目的成果将解决气候和地貌过程之间的一级联系，并测试评估景观如何随着千年尺度气候和植被变化而演变的新兴数值模型。该研究项目旨在记录和量化过去4万年中气候和植被的变化如何影响陡峭的森林景观的侵蚀率。预期的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（例如与木材采伐有关的变化）非常重要。虽然有许多数值模型可以预测景观对气候变化的调整，但对控制方程的理解很少，特别是植被的作用需要大量的定量研究。通过研究山区湖泊中保存的详细沉积记录，研究结果将揭示生态系统和景观是如何共同进化形成现在的地形的。这些结果还应该揭示在最近的地质历史中，是否发生了“事件”或快速地表变化的时期，以响应气候或植被变化。

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.