Habitat-modifying weeds such as the alien melastome Miconia calvescens represent a major threat to native biodiversity.

Bringing active threat abatement management to priority conservation areas is the primary goal.

Threats

Over human history in the islands, several major groups of alien species have emerged as the most damaging to native ecosystems and species:

o        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 ecological systems.

o        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 Hawai‘i than there are native species. Perhaps 200 of these are ex­treme­ly aggressive, habitat-modifying weeds.

o        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, conservation in Hawai‘i de­pends more than anything on keep­ing re­maining, rela­tively uninvaded native areas intact, stem­ming the es­tab­lish­ment of new in­va­sive species, and devising practical strategies to limit the impact of widely-established species.

 Wildfire in Hawai'i is invariably followed by invasion by fire-adapted alien grasses and shrubs, creating a cycle of destruction for native species and ecosystems. 

Mosquitos carry diseases such as avian malaria; deadly to endangered forest birds.

Goats and sheep are a prevailing threat to drier native areas in Hawai‘i.


Development remains a threat on O'ahu, where 80% of the state's population resides.

Threat Summary (continued from above)

Fire:  Wildfire is an uncommon natural occurrence in Hawai‘i, where ground-strike lightning is rare and wet plant communities cover large areas.  Fire-adapted aliens (especially grasses and short-lived shrubs) are established in lower, leeward slopes and some subalpine areas.  Normally ignited by people, these weeds fuel major wildfires that can carry into native forests. Native forests are destroyed and replaced with fire-adapted weeds in a trend that increases the range and intensity of these fires. 

Rodents are important egg predators in forest bird concentration areas.

Small Mammals: There are no native small mammals (e.g., rodents, cats, dogs, rabbits, mongooses) in Hawai‘i, and the ecological effects of either herbivorous, omnivorous, or predatory small mammals is to reduce populations of native species, sometimes to extinction. Rodents are implicated in damage to 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 Wai'anae conservation area of O‘ahu, where they affect endangered tree snails, rare native plants, and an endangered forest bird, the ‘elepaio (Chasiempis  sandwichensis gayi).

Military training activities:  Live-fire training, large-scale troop movements, and heavy equipment operation are serious threats to native species at U.S. Army training facilities in the O‘ahu and Hawai‘i conservation areas.  Training operations have resulted in clearing of native vegetation, increased wildfire, and the introduction and spread of unwanted alien species.  The 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.

Recreational use: Typical recreational uses of native ecosystems include hiking, camping, 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.

Stream diversion:  Native stream communities are highly dependent on continuous stream flows to the sea to 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 Hawai‘i State Water Code provides mechanisms for protecting stream flow, but these mechanisms await their first test cases.

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 a large, commercial scale in most situations, and are already restricted by permit systems.

Logging:  Although logging and other high-intensity harvesting is no longer widespread in Hawai‘i (most loggable areas were cleared in the last century), these and other clearing practices are important concerns in some conservation areas on Hawai‘i Island. Commercial logging of native koa (Acacia koa), ‘ōhi‘a (Metrosideros spp.), sandalwood (Santalum spp.), and hāpu‘u tree ferns (Cibotium spp.) are approaching the limits of available resources, and the forest products industry supports planting programs to restore former forest lands. 

Grazing:  Clearing of forest for production of cattle has a 200 year history in Hawai‘i. Cattle, being large ungulates, have the same damaging effects on native vegetation as other ungulates, and the devastating effects of cattle in Hawai'i have been well documented. Today, there remain 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.