Ecosystem Processes: Tropical Ecosystems
Restoration of Ecosystem Processes:
"Ecosystem restoration is an activity at which everyone wins: when successful, we are rewarded by having returned a fragment of the earth's surface to its former state; when we fail, we learn an immense amount about how ecosystems work, provided we are able to determine why the failure occurred."
John J. Ewel
Hawai'i, the most remote archipelago on Earth, is a textbook example not only of the evolutionary results of isolation, but also the environmental consequences of colonization. Humans, and the plants and animals they introduced, are relatively recent arrivals in Hawai'i, and their combined impacts have devastated local biota and whole ecosystems. Although the impact of Polynesian settlement was substantial, the scale of land use changes expanded since about 1850 when EuroAmerican settlement and influence was well established.
After decades of land abuse and deforestation, there is increasing interest in restoring native forest ecosystems to conserve native biodiversity, provide wildlife habitat, and restore important ecosystem processes such as watershed protection. There is also considerable interest in using non-native species to restore forest ecosystem functioning to degraded lands that will no longer readily support native communities. Similar deforestation problems plague most of the tropics, and solutions developed in Hawai'i have potential applicability elsewhere.
The Institute of Pacific Islands Forestry's goal is to provide a scientifically sound basis for the reconstruction and functioning of damaged ecosystems that are self-supporting and, at least to some degree, resilient to subsequent change. Research in Hawai'i, the Federated States of Micronesia and Costa Rica is providing information on how different species interact with each other and their environment during ecosystem development, as well as on specific requirements of tree species being used in restoration efforts. The impacts of past land rehabilitation actions on subsequent recovery of biological diversity and restoration of ecosystem processes are being examined in Hawai'i plantations that are dominated by native or introduced species. Problems specific to re-establishment of Metrosideros-Acacia forests on rangelands for endangered species habitat are being studied at high elevation sites in Hawai'i. The HUERTOS project in Costa Rica focuses on processes and mechanisms that influence soil fertility and sustainability, using fast growing model communities whose species composition and rotation frequency are investigator-controlled. Changes in structure and functioning of primary, secondary, and human-made forest of the Pacific islands are also being considered.
Organization for Tropical Studies, La Selva Biological Station (Costa Rica), HUERTOS
Native forest ecosystem restoration
The 33,000-acre Hakalau Forest National wildlife Refuge, located on the windward slopes of Mauna Kea, island of Hawai'i, was established in 1985 to protect five endangered forest birds and 29 rare or endangered plants. While most of the refuge contains some of the finest remaining montane rainforest in Hawai'i, about 5,000 acres was converted to non-native grassland over the last 150 years. Restoring native forest to these sites is an essential step for recovering and protecting threatened and endangered species.
Research is focused on (1) identifying factors limiting natural and artificial regeneration of native species in grasslands and (2) developing techniques for alleviating those constraints. Acacia koa trees establish naturally and after planting, but other native species establish slowly or not at all. The factors most likely influencing establishment are competition by alien grasses, low availability of nitrogen and phosphorus, sub-zero temperatures, high UV radiation, lack of effective mycorrhizae, low seed input, and lack of suitable seedbeds. All factors are potentially affected by establishment of N-fixing A. koa trees. Studies of these factors involve partners from the University of Hawaii, Oregon State University, and Stanford University.
Role of plantations in restoration of ecosystem processes
Restoration of severely degraded landscapes can be accomplished by the establishment of alien trees, which are often more tolerant of harsh site conditions than are native species. Tree plantations can facilitate re-establishment of native plant species through effects on soil fertility and water relations, forest floor structure, and understory microclimate.
In Hawai'i, plantations of non-native tree species have been established for watershed protection since the 1920s. Some plantations have diversified and contain a rich array of native species, while others have resisted invasion and remain monospecific stands. Although these plantations were not originally established to recreate all the attributes of the original ecosystems, they present a unique restoration laboratory in which to study the effects of the plantation tree species on (1) native plant richness and biodiversity and (2) various aspects of ecosystem functioning. Such research is under way in The Nature Conservancy's Honouliuli Preserve. This forested Preserve on the windward slopes of the Wai'anae mountains forms a major part of the watershed above a region targeted for the highest population growth on the island of O'ahu. Cooperators from the University of Hawaii are working with us to determine species' effects on the hydrologic cycle and regulation of water use in the plantations.
Research conducted by: