Sediment export and its controls during secondary forest succession

土地利用和土地覆盖变化的生态后果已经通过许多科学研究进行了调查，公众非常感兴趣，因为这些变化直接影响到数百万人的日常生活。在许多热带国家，古老的森林仍然以惊人的速度丧失，但与此同时，社会变迁和向城市的迁移导致次生演替森林的数量大幅增加。了解这些大规模土地覆盖变化的后果对于基础研究和土地利用规划都很重要。不幸的是，现有的科学文献严重偏向于涉及生物方面的研究，而令人惊讶的是，关于次生森林演替过程中侵蚀过程的变化，人们知之甚少。此外，目前尚不清楚森林再生如何控制热带地区的侵蚀速度，因为热带地区自然容易激活地表径流和土壤流失。由于地上和地下恢复速度不匹配，我预计这些地区在次生森林演替的早期阶段会出现泥沙输出的高峰。要验证这一假设，需要量化类似土壤上但被不同阶段的次生演替植被覆盖的集水区的悬浮泥沙输出。为了实现我的目标，我建议在演替的不同阶段对8个森林站点的悬浮沉积物进行基于事件的自动采样。拟议的沉积物采样活动将伴随着对降雨期间排水网络扩展的监测，以及对森林结构和土壤参数的详细实地调查。这些实地数据和最先进的泥沙输出统计模型将使我能够评估次生森林演替期间侵蚀过程的变化，并确定观察到的侵蚀过程变化的驱动因素。我预计拟议的研究结果将引发一场关于森林生态系统侵蚀过程的时间和空间变异性的辩论。鉴于热带国家受森林演替影响的面积很大，拟议工作的结果不仅具有科学价值，而且在水质管理方面也具有社会经济意义。

The ecological consequences of land-use and land-cover changes have been investigated by numerous scientific studies and are of great interest to the general public because these changes have a direct impact on the daily lives of millions of people. In many tropical countries, old-growth forests are still lost at an alarming rate but at the same time, social shifts and migration into cities result in a substantial increase of secondary succession forests. Understanding the consequences of these large-scale land-cover changes is important both for basic research and land-use planning. Unfortunately, the available scientific literature is strongly biased towards studies dealing with biotic aspects, whereas surprisingly little details are known with respect to changes of erosion processes during secondary forest succession. Moreover, it is currently unknown how forest regrowth controls erosion rates in tropical regions that are naturally prone to the activation of surficial flow paths and soil loss. Due to a mismatch between aboveground and belowground recovery rates, I anticipate that these areas show a peak of sediment export during early stages of secondary forest succession. Testing this hypothesis requires quantifying suspended-sediment exports of catchments on similar soils but covered with different stages of secondary succession vegetation. To achieve my objectives I propose an event-based, automated sampling of suspended sediment at 8 forest sites in various stages of succession. The proposed sediment sampling campaign will be accompanied by a monitoring of the drainage network expansion during rainfall events and detailed field investigations of forest structure and soil parameters. These field data and state-of-the-art statistical modeling of sediment export will allow me to assess the change of erosion processes during secondary forest succession and to identify the drivers of the observed changes of erosion processes. I expect that the results of the proposed research will trigger a debate on the temporal and spatial variability of erosion processes in forest ecosystems. Given the large area which is subject to forest succession in tropical countries, the findings of the proposed work are not only of scientific interest but they are also - in the context of water-quality management - of socio-economic relevance.