The Hawaiian Islands are the most isolated archipelago in the world, situated in the middle of the Pacific Ocean more than 3,200 kilometers (2,000 miles) from the nearest continent. Due to its extreme isolation and climactic conditions, Hawaii is characterized by high levels of endemism in both its native animals and plants, with over 10,000 species found nowhere else on earth. Although thousands of Hawaiian species have yet to be described, the estimated number of native species is thought to include more than 14,000 terrestrial, 100 freshwater, and 6,500 marine taxa. For more than 70 million years, the evolution of new species vastly exceeded losses to extinction. Yet after the arrival of humans to the islands, about 700 years ago, numerous extinctions have occurred and many more species are threatened. These losses include more than half of the endemic birds, including flightless ducks, rails, and ibis, hundreds of plant species, and possibly thousands of lesser known taxa such as terrestrial insects and spiders that were lost before they were ever described.
Because of this extreme isolation, relatively few species have colonized the archipelago and only a subset of these successfully establish populations over the islands’ 70 million year history. Those that did, however, found a diversity of habitat types because of elevation and climate gradients. Extremely limited or no gene flow from their distant, original populations, facilitated the rapid adaptation of colonists to their novel environments. For many such colonists, unique adaptations occurred simultaneously among populations that were isolated from one another on an island and between islands. Hawaii provides a text-book example of adaptive radiation, the process by which many new species evolved from a single common ancestor in a relatively short time span.
Although comprising less than 0.2 percent of the land area of the United States, the Hawaiian Islands hold more than 30 percent of the nation’s federally listed species, including 317 taxa of plants and animals listed by the U.S. Fish and Wildlife Service (USFWS) as endangered or threatened, 12 taxa proposed as endangered and 105 taxa as candidates for listing. Unique and varied habitats are also found across the islands. As a result, Hawaii presents both an opportunity and a challenge for conservation.
In 2005, Congress required all states to develop a Comprehensive Wildlife Conservation Strategy (CWCS).i The CWCS’s are to be updated every five years. In Hawaii, this provides the opportunity for resource managers to develop and modify a comprehensive planning process to help manage all of Hawaii’s unique native wildlife. The CWCS recognizes the importance of protecting all native terrestrial animals, all endemic aquatic wildlife, other aquatic species threatened with decline, and a broad range of native flora. On the ecological level, the CWCS takes a habitat management approach, adopting a landscape view that takes into account the complex inter-relationships between species and their habitats and the need for change and adaptability. This plan builds on and synthesizes information gathered from existing conservation partnerships and cooperative efforts. Additionally, it highlights partnerships and their efforts in Hawaii with a goal to Map 6.1 Major vegetation types for the Island of Hawaii before the arrival of humans and at present time. Map by Page Else, Hawaii Conservation Alliance.
enhance and expand existing and to create new partnerships, ultimately increasing support for implementing Hawaii’s wildlife strategy.
The DLNR coordinated the development of Hawaii’s CWCS, with joint cooperation by the Division of Forestry and Wildlife (DOFAW) and the Division of Aquatic Resources (DAR), the divisions primarily charged with protecting the State’s terrestrial and aquatic resources. The foundation for this assessment of Hawaii’s Biodiversity was derived from the CWCS with up-to-date data on Hawaii’s habitats and species contributed collaboratively by DOFAW staff, The Nature Conservancy and other Hawaii biodiversity and wildlife experts. The assessment provides an overview of the range of species found in Hawaii and offers a number of strategies that could positively impact the conservation of biodiversity in these islands.
Benefits & Services
In present day Hawaii, the link between native Hawaiian culture and native species continues to be practiced in belief systems as well as traditional practices such as gathering of native plants and animals for hula, traditional medicines, food, structural materials, carving, weaving, tool making, jewelry, and ceremonies. For many native Hawaiians, the relationship with the land and native ecosystems is integral to their identity and sense of well-being. The special role and relationship native Hawaiians have with some native species and ecosystems in the islands is perhaps best reflected in their increasing role in natural resource management in places such as the island of Kahoolawe; Limahuli and Lumahai valleys on Kauai; Moomomi, Molokai; and Keauhou, Hawaii where traditional management practices such as kapu (taboo) and ahupuaa (watershed)-scale thinking predominate.
Native biodiversity is not only important to native Hawaiians, but also to many non-Hawaiian residents and to many outside of the islands. Active local lifestyles may include activities such as hiking, backpacking, snorkeling, boating, fishing, and hunting and are enhanced when interacting with native wildlife and ecosystems unique to the Hawaiian islands. Based on a 2004 survey “Wildlife Values in the West”, a large majority of Hawaii’s residents (71.4%) strongly agree that it is important to take steps to prevent the extinction of endangered species.ii Economically, wildlife viewing opportunities have become an important part of the State’s $10 billion a year tourism industry.iii Hawaii’s native wildlife and their habitats also provide essential goods and services to residents such as water quality, soil stabilization, carbon storage, and climate control. A University of Hawaii study of the economic value of these services estimated between $7.4 to $14 billion in the Koolau Mountains on Oahu alone.iv Other examples of ecological services provided by native habitats include coral reefs that protect beaches, homes, and businesses from erosion, storms, and tsunami waves; wetland habitats that filter the water supply, mitigate pollution, and slow storm runoff; and other natural areas that provide social and human health benefits through recreation, beauty and a spiritual connection to nature.
Map 6.2 Major vegetation types for the Maui Nui (Maui, Lanai, Molokai and Kahoolawe ) before the arrival of humans and at present time. Map by Page Else, Hawaii Conservation Alliance.
Forest conservation plays a critical role in maintaining the health of makai (ocean) resources such as coral reef ecosystems and limu (seaweed) beds. Local wisdom passed on by kupuna (elders) cautions that unless we take care of mauka resources, makai resources will suffer.
The Hawaiian Archipelago possesses a wide range of habitats, from wet forests to extremely dry coastal grasslands and subalpine areas. With the arrival of humans and consequent clearing of native habitats for agriculture, the introduction of invasive species and more recently development, many of these habitats have declined. Maps 6.1, 6.2 and 6.3 depict major vegetation types before human arrival and their current extent. For example, an estimated 90 percent of Hawaii’s dryland habitat, 61 percent of the mesic habitat, and 42 percent of wetlands habitats have been lost. Today, native vegetation occurs over less than 40 percent of the islands’ land area. Similarly, much of the habitat for freshwater species has declined, with 58 percent of the perennial streams in the State having been altered in some way.
Map 6.3 Major vegetation types for the Kauai, Niihau and Oahu before the arrival of humans and at present time. Map by Page Else, Hawaii Conservation Alliance.
The distribution of terrestrial habitats in Hawaii is influenced by elevation, climate, and substrate. Using elevation zones and moisture gradients, Hawaii can be classified into nine terrestrial habitat types. These nine habitat types can be further refined based on the dominant plants and structural characteristics of the vegetation. The Manual of the Flowering Plants of Hawaiiv recognizes 33 native forest communities, 36 native shrubland communities, eight native grassland communities, and four native herbland communities. Subterranean systems form a tenth habitat type defined by geology rather than elevation zones and moisture.
Aquatic habitats link together most of Hawaii’s terrestrial habitats. Streams and groundwater flow play an important role in providing water for plants and animals throughout the ecosystem. The flow of water that rains down on the high mountaintops transports nutrients, and organic matter through the various forested and shrubland areas into estuaries and wetlands at low elevations and then finally into the ocean. Many of Hawaii’s native freshwater aquatic animals migrate between the ocean, estuaries, and upper reaches of streams as part of their life cycle.
This interconnected network of streams and the adjacent land areas collectively is referred to as a watershed, similar to the traditional Hawaiian land division ahupuaa. Activities or threats that affect one part of this interconnected system will affect some other part, thus affecting the whole of the system. To effectively protect watersheds, the entire ahupuaa must be maintained or allowed to restore itself. Equally important are marine ecosystems, which are affected by pollution and/or onshore activities. Therefore, effective conservation of terrestrial habitats has direct relevance to the health of marine ecosystems.
Seventy-five percent of plant and animal extinctions documented in the United States have occurred in Hawaii. Today, Hawaii has the highest number of threatened and endangered species in the United States accounting for more than 30 percent of all federally listed taxa. The decline in native species is also mirrored by the loss of native habitat, with less than 40 percent of the land surface covered with native-dominated vegetation today.
The Hawaii CWCSvi selected a large cohort as Species of Greatest Conservation Need including: one terrestrial mammal, 77 birds, over 5,000 known terrestrial invertebrates, over 500 plants, six species of endemic terrestrial algae, 12 freshwater invertebrates, five freshwater fishes, 24 species of endemic freshwater algae, 20 anchialine-pond associated fauna, 26 marine mammals, six marine reptiles, 154 marine fishes, 197 marine invertebrates, and 79 species of endemic marine plants or algae.
The current, most pervasive threats to Hawaiian biodiversity in Hawaii are non-native invasive, habitat-modifying plants, animal and disease. For many endangered species, small populations make recovery difficult. Fire, residential development, and military training are also important at specific locations. Threats include some that are pervasive across all conservation areas in the archipelago and some that are specific to particular places (See Table 6.1 Terrestrial Habitats and Principal Threats to Native Ecosystems).
Table 6.1. Terrestrial Habitats & Principal Threats to Native Ecosystems
Rooting pigs (pigs also spread habitat modifying invasive plants); logging; conversion to pastureland
Conversion to pastureland; invasive grasses; feral goats, sheep & pigs, wildfire, clearing for commercial tree planting
Invasive plants and grazing by feral goats, sheep & mouflon
Establishment & spread of invasive plants, especially kahili ginger & strawberry guava and degradation of the understory by feral pigs
Most converted to agriculture, ranching or logging, remaining threatened by a number of invasive plant species, wildfire, feral ungulates and introduced game animals, particularly goats, pigs and axis deer
Most converted to urban & residential use; degraded by fire, grazing, and invasive grasses, particularly fountain grass, beard grass and natal red top - these grasses constitute a major fire threat
Conversion to residential development, introduced plant species, off road vehicles and arson
Degradation of habitat, habitat loss to development, invasive invertebrates
Invasive alien species: The continuing invasion of alien weeds, predators, herbivores, pathogens, and competitors into native ecosystems is the engine that currently drives the Hawaiian extinction crisis. Since the establishment of forest reserves, during the first three decades of the 20th century, alien invasion —not direct habitat destruction by humans—has been the dominant threat to native species and ecosystems across the Hawaiian Islands.
Hawaii is extraordinarily vulnerable to human-accelerated alien species invasions due to: (1) its geographic isolation as the hub of Pacific travel and trade, and (2) an exceptional range of hospitable habitats for invaders to occupy. The estimated rate for successful, new colonization of the islands by a plant or animal species before human arrival was once every 25,000 - 50,000 years. In contrast, over the past 30 years, newly established species have been recorded in Hawaii at the rate of once every 18 days. The existing complement of established invasive aliens has the capacity to overwhelm most remaining native habitat if left unchecked.
Over human history in the islands, several major groups of alien species have emerged as the most damaging to native ecosystems and species:
Ungulates – Lacking any large native herbivorous mammals, the Hawaiian flora is not adapted to ungulate browsing or trampling. Feral pigs, goats, sheep, deer, and cattle were responsible for destruction of lowland ecosystems, and continue to degrade remaining native ecosystems.
Invasive weeds – Through a history of increasing introduction of alien plants, there are now more species of naturalized alien vascular plants in the wilds of Hawaii than there are native species. An estimated 200 of these are extremely aggressive, habitat-modifying weeds.
Predators – Small mammals such as rats, mongoose, and feral cats prey on native birds. Rats are implicated as wholesale vegetation modifiers via selective seed predation. Predatory invertebrates such as ants and other social Hymenoptera have greatly disrupted invertebrate communities at all elevations, particularly in the lowlands.
For these reasons, successful conservation in Hawaii requires keeping remaining, relatively uninvaded native areas intact, stemming the establishment of new invasive species, restoring degraded areas needed for species-specific conservation goals, and devising practical strategies to limit the impact of widely-established species. Table 6.1 reveals that alien species such as ungulates and weeds are prominent and ubiquitous, with other threats active in specific locations.
Climate Change: Rising sea levels, increased climate variability, and increased flooding threaten native biodiversity through the change in baseline moisture and temperature conditions. Climate change has invariably played a role in the frequency of fires on the leeward sides of many of the Hawaiian Islands, as well as the nearly total loss of the dryland forests.
Development: Widespread conversion and development of the lowlands in Hawaii took place from prehistoric times to present day. Following statehood, the implementation of strong conservation zoning laws has largely limited development of natural areas and forest reserves. However, incremental conversion of lowland native areas continues on the most densely populated island (Oahu), as well as the largest island (Hawaii), particularly in Windward Mauna Loa and Kailua Kona. Development also impacts important agricultural areas that render the human populations more dependent on imports for daily needs.
Grazing: Clearing of forest for production of cattle has a 200 year history in Hawaii. Cattle have the same damaging effects on native vegetation as other ungulates, and the devastating effects of cattle in Hawaii are well documented. Today, there are still a number of very large private ranches, several of which occur within native ecological systems. Ranching-related loss of native ecosystems is active in the Kona conservation area in particular. There is a long history of the state providing extremely low cost leases to ranchers on state lands, which perpetuates grazing impacts on already degraded lands and the loss of more cattle (feral) into forested areas.
Logging: Although logging and other high-intensity harvesting is not practiced widely in Hawaii (most high timber value areas were cleared in the last century), these and other clearing practices are important concerns in some conservation areas on Hawaii Island. Commercial logging of native koa (Acacia koa), ohia (Metrosideros spp.), sandalwood (Santalum spp.), and hapuu tree ferns (Cibotium spp.) are approaching the limits of available resources, and the forest products industry supports planting programs to restore former forest lands. On the Hamakua Coast on Windward Hawaii Island, vast mesic and lowland areas, formerly dominated by sugar cane, have been planted with eucalyptus species and are awaiting a viable logging industry for harvest. This could stimulate the harvest of more adult hardwood stands and strike the need for aggressive replanting and sustainable harvest practices. (See Issue 8: Forest Products and Carbon Sequestration for additional information.)
Military training activities: Live-fire training, large-scale troop movements and heavy equipment operations are serious threats to native species at U.S. Army training facilities in areas of Oahu and Hawaii Island. Training operations have resulted in vegetation clearing, increases in wildfire frequency, and the introduction and spread of unwanted alien species. The U.S. Army has instituted an ecosystem management program to mitigate these impacts, and is now among the state’s most active and well-funded stewards of native systems. The U.S. Army and other military branches in Hawaii also have acquisition buffer programs that have played important roles in acquiring important threatened and endangered species habitat. (Please refer to Appendix C: Forestry Related Assistance Programs for more information).
Overharvesting: Most minor forest and stream “commodities” (plant materials for lei making, flower arrangements, and herbal use; stream fishes and invertebrates for food) can be harvested for home and cultural use on a sustainable basis. These activities are not sustainable at the commercial scale, however, and are restricted by permit systems. Similar issues prevail in the seaweed and fishing industries.
Pathogens (including invertebrate pests): Diseases and pests can play an important role in reduction of viability of native species, and indirectly, the natural communities and ecological systems comprised of these species. Pathogens and pests related to declines in native species include mosquitoes and mosquito-borne diseases (avian malaria and pox), ants (various species), Erythrina Gall Wasp (Quadrastichus erythrinae), Two-Spotted Leafhopper (Sophonia rufofascia), slugs (various species), and Black Twig Borer (Xylosandrus compactus). Often the role of pathogens is tied to other threats. For example, avian diseases affecting native forest bird concentrations are spread by mosquitoes, and spread of mosquitoes into forest bird habitat is tied to wallows of feral pigs that create mosquito breeding sites where none otherwise existed. Proliferation of diseases across taxa can be common in Hawaii due to the fragility and vulnerability of these ecosystems.
Recreational use: Typical recreational uses of native ecosystems include hiking, camping, hunting and off-road vehicle touring. Restrictions on damaging activities in the state conservation district somewhat limits the impacts of recreational use, although indirect effects of recreational activities such as hiking, e.g., spread of invasive weeds, has been documented. Hunting is also a very important sport and source of food for many people in Hawaii. There is much disagreement on how to manage feral ungulates in such a way that they do not devastate native forests, but also continue to maintain a viable hunting capacity.
Small Mammals: There are no native small mammals (e.g., rodents, cats, dogs, rabbits, mongooses) in Hawaii. The long term ecological effects of herbivorous, omnivorous and predatory small mammals has drastically reduced populations of native species, sometimes to extinction. Rodents damage lowland forests via seed predation, as well as on both ground-nesting seabirds and forest birds. Feral cats and dogs impose similar impacts. Rodents seem particularly damaging in the Waianae conservation area of Oahu, where they affect endangered tree snails, rare native plants, and an endangered forest bird, the elepaio (Chasiempis sandwichensis gayi).
Stream diversion: Native stream communities are highly dependent on continuous stream flows to the sea that support the diadromous life cycles of their dominant aquatic animals. Most of the state’s streams are already partially or fully altered (channelized, diverted, or de-watered via groundwater pumping), and those that remain are vulnerable as the demand for fresh water outstrips the current yield of harvesting. The new Hawaii State Water Codevii provides mechanisms for protecting stream flow, but these mechanisms await their first test cases.