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

由于过去的土地使用、物种灭绝和非本地物种的入侵，地球上很大一部分荒地已经退化。退化的生态系统通常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。这项研究解决了热带森林生态系统已经退化，过去的森林砍伐和本地水果分散鸟类的损失，并询问为什么这些森林没有恢复到本地物种的主导地位，尽管停止了原来的干扰，造成他们的退化。 它评估了广泛的入侵牧草，高水平的土壤氮，和重要的本地物种（鸟类，以前占主导地位的本地树木，土壤微生物）的损失在阻碍森林恢复的相互作用。这项工作还讨论了为什么大规模重新种植单一本土树种的常见恢复方法不会导致本土热带森林的恢复。这项研究将提供夏威夷特有森林物种生长需求的迫切需要的信息，并将有助于指导恢复行动，以确保更好地成功重建多样化的原生森林，这可能会为未来的恢复项目节省成本。本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。通过本研究，将深入了解替代稳定状态理论，该理论已成为生态系统退化和恢复的主要讨论内容。这一理论的一个关键假设是，当前的条件产生了阻碍变化的反馈或优先效应，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集中在减缓生态系统变化的特定个体反馈的作用。使用退化的山地热带森林在夏威夷作为一个研究系统，本研究解决了多重反馈的作用，包括跨营养水平的，在干扰，或相反地允许，社区发展远离一个看似非瞬态退化状态。一个跨学科的团队将解决鸟类种子传播的重要性和相互作用，上层树木的组成，林下草与分散幼苗的竞争，以及植物土壤和菌根反馈，在保持持续退化的条件。该研究测试了鸟类，植物，氮可用性和真菌之间的特定相互作用，使用操纵性田间实验，温室反馈研究和生态建模。该小组将共同努力，确定需要采取何种管理行动组合，以加速生态系统朝着土地管理者所希望的方向变化。

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.