| 英文摘要: | 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. |