Sediment export and its controls during secondary forest succession

土地使用和土地覆被变化的生态后果已由许多科学研究进行了调查，并引起公众的极大兴趣，因为这些变化直接影响到千百万人的日常生活。在许多热带国家，原始森林的消失速度仍然令人震惊，但与此同时，社会变迁和向城市的移民导致次生演替森林大量增加。了解这些大规模土地覆盖变化的后果对基础研究和土地利用规划都很重要。不幸的是，现有的科学文献是强烈偏向于处理生物方面的研究，而令人惊讶的是，很少的细节是已知的次生林演替过程中的侵蚀过程的变化。此外，目前还不知道森林再生如何控制热带地区的侵蚀率，因为热带地区自然容易激活表层水流动路径和土壤流失。由于地上和地下的恢复率之间的不匹配，我预计，这些地区显示出沉积物出口的高峰在次生林演替的早期阶段。检验这一假设需要量化悬浮泥沙出口集水区类似的土壤，但覆盖着不同阶段的次生演替植被。为了实现我的目标，我提出了一个基于事件的，自动化采样的悬浮沉积物在8个森林网站在不同阶段的继承。在进行拟议的沉积物取样活动的同时，还将监测降雨期间排水网络的扩展情况，并对森林结构和土壤参数进行详细的实地调查。这些实地数据和最先进的统计模型的沉积物输出将使我能够评估在次生林演替过程中的侵蚀过程的变化，并确定所观察到的侵蚀过程的变化的驱动因素。我预计，拟议的研究结果将引发对森林生态系统侵蚀过程的时间和空间变异性的辩论。鉴于热带国家森林演替的地区很大，拟议工作的结果不仅具有科学意义，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.