Collaborative Research: Do ecological feedbacks across trophic levels affect alternate stable states and restoration of tropical forests?

由于过去的土地利用、物种灭绝和外来物种的入侵，地球上相当大一部分的荒地已经退化。退化的生态系统往往不能像完整的系统那样为人类提供同样重要的服务，包括防止侵蚀、控制洪水和支持野生动物等服务。本研究解决了由于过去的森林砍伐和原生水果传播鸟类的丧失而退化的热带森林生态系统，并提出了为什么尽管导致其退化的原始干扰停止了，这些森林却没有恢复到原生物种优势的原因。它评估了广泛的入侵牧草、高水平的土壤氮和重要本地物种（鸟类、以前占主导地位的本地树木和土壤微生物）的丧失在阻碍森林恢复中的相互作用。这项工作还解决了为什么大规模重新种植单一原生树种的常见恢复方法不能导致原生热带森林的恢复。这项研究将为夏威夷特有森林物种的生长需求提供急需的信息，并将有助于指导恢复行动，以确保更好地重建多样化的原始森林，这可能会为未来的恢复项目节省成本。该项目还将培训当地学生，他们将成为这些生态系统的未来管理者。对替代稳定状态理论的洞察，这已经成为主导讨论的生态系统退化和恢复，将获得与本研究。该理论的一个关键假设是，当前的条件产生了反馈或优先效应，使变化停滞不前，从而阻碍了处于退化状态的生态系统的恢复。关于这一主题的大多数研究都集中在特定个体反馈在减缓生态系统变化中的作用上。利用夏威夷退化的山地热带森林作为研究系统，本研究解决了多种反馈的作用，包括跨营养级反馈，在干扰或相反地允许社区发展远离看似非短暂的退化状态。一个跨学科团队将研究鸟类种子传播、林下树木组成、林下草与分散幼苗的竞争以及植物-土壤和菌根反馈在维持持续退化条件中的重要性和相互作用。本研究通过野外操作试验、温室反馈研究和生态模型，测试了鸟类、植物、氮有效性和菌根之间的特定相互作用。该小组将共同努力，确定需要哪些管理行动组合来加速生态系统朝着土地管理者所期望的方向变化。

A substantial portion of the Earth's wildlands have been degraded by past land use, species extinctions and invasion by non-native species. Degraded ecosystems often do not provide the same important services to humans as intact systems - including such services as erosion prevention, flood control, and support for wildlife. This research addresses tropical forest ecosystems that have been degraded by past forest clearing and the loss of native fruit-dispersing birds and asks why these forests are not returning to native species dominance despite the cessation of the original disturbances that caused their degradation. It evaluates the interacting roles of widespread invasive pasture grasses, high levels of soil nitrogen, and loss of important native species (birds, a previously dominant native tree, and soil microorganisms) in stalling forest recovery. The work also addresses why the common restoration method of mass replanting of a single native tree species does not lead to recovery of native tropical forest. This research will provide badly needed information on growth requirements for endemic Hawaiian forest species and will help direct restoration actions to insure better success in recreating diverse native forests, which may result in cost savings for future restoration projects. This project will also train local students who will become the future stewards of these ecosystems.Insight into the theory of alternative stable states, which has come to dominate discussions of ecosystem degradation and restoration, will be gained with this research. A key assumption of this theory is that current conditions create feedbacks or priority effects that stall change, thus hindering recovery of ecosystems that exist in a degraded state. Most research on this topic focuses on the role of particular individual feedbacks in slowing ecosystem change. Using degraded montane tropical forests in Hawaii as a study system, this research addresses the role of multiple feedbacks, including cross-trophic level ones, in interfering with, or conversely allowing, community development away from a seemingly non-transient degraded state. An interdisciplinary team will address the importance and interactions of avian seed dispersal, overstory tree composition, understory grass competition with dispersing seedlings, and plant-soil and mycorrhizal feedbacks in maintaining persistent degraded conditions. The research tests specific interactions between birds, plants, nitrogen availability and mycorrhizae using manipulative field experiments, greenhouse feedback studies and ecological modeling. Together the team will work to determine what combinations of management actions are needed to accelerate ecosystem change in the direction desired by land managers.