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 isthe primary goal.

Threats

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

o        Ungulates – lacking any large native herbivorousmammals, the Hawaiian flora is not adapted to ungulate brows­ing or trampling.Feral pigs, goats, sheep, deer, and cattle were responsible for de­struc­tionof lowland ecosystems, and continue to degrade re­main­ing native ecological systems.

o        Invasive weeds – through a his­tory ofincreasing introduction of alien plants, there are now more species of nat­u­ral­izedalien 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 wholesalevegetation modifiers via selective seed pre­da­tion. Predatory invertebratessuch as ants and other social hymenoptera have greatly disrupted in­ver­te­brate communities at allelevations, par­tic­ularly in the lowlands.

For these reasons, conservationin Hawai‘i de­pends more than anything on keep­ing re­maining, rela­tivelyuninvaded native areas intact, stem­ming the es­tab­lish­ment of new in­va­sivespecies, and devising practical strategies to limit the impact ofwidely-established species.

 Wildfirein Hawai'i is invariably followed by invasion by fire-adapted aliengrasses and shrubs, creating a cycle of destruction for native speciesand ecosystems. 

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

Goats and sheep are a prevailing threat to drier native areasin 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 inHawai‘i, where ground-strike lightning is rare and wet plant communities coverlarge areas.  Fire-adapted aliens(especially grasses and short-lived shrubs) are established inlower, leeward slopes and some subalpine areas. Normally ignited by people, these weeds fuel major wildfires that cancarry into native forests. Native forests are destroyed and replaced with fire-adaptedweeds 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, andthe ecological effects of either herbivorous, omnivorous, or predatorysmall mammals is to reduce populations of native species, sometimes toextinction. Rodents are implicated in damage to lowland forests viaseed predation, as well as on both ground-nesting seabirds and forestbirds. Feral cats and dogs impose similar impacts. Rodents seemparticularly damaging in the Wai'anae conservation area of O‘ahu,where they affect endangered tree snails, rare native plants, and anendangered forest bird, the ‘elepaio (Chasiempis  sandwichensis gayi).

Military training activities:  Live-fire training, large-scale troopmovements, and heavy equipment operation are serious threats to native speciesat U.S. Army training facilities in the O‘ahu and Hawai‘i conservation areas.  Training operations have resulted in clearingof native vegetation, increased wildfire, and the introduction and spread ofunwanted alien species.  The Army hasinstituted an ecosystem management program to mitigate these impacts, and isnow 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 inthe 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:  Nativestream communities are highly dependent on continuous stream flows to the seato support the diadromous life cycles of their dominant aquatic animals.  Most of the state’s streams are alreadypartially or fully altered (channelized, diverted, or de-watered viagroundwater pumping), and those that remain are vulnerable as the demand forfresh water outstrips the current yield of harvesting. The new Hawai‘i State Water Code providesmechanisms for protecting stream flow, but these mechanisms await their firsttest cases.

Overharvesting: Most minor forest and stream “commodities”(plant materials for lei making, flower arrangements, and herbal use; streamfishes and invertebrates for food) can be harvested for home and cultural use on asustainable basis.  These activities arenot sustainable at a large, commercial scale in most situations, and arealready restricted by permit systems.

Logging:  Although logging andother high-intensity harvesting is no longer widespread in Hawai‘i (mostloggable areas were cleared in the last century), these and other clearingpractices are important concerns in some conservation areas on Hawai‘i Island. Commercial logging of native koa (Acaciakoa), ‘ōhi‘a (Metrosideros spp.),sandalwood (Santalum spp.), and hāpu‘utree ferns (Cibotium spp.) areapproaching the limits of available resources, and the forest products industrysupports planting programs to restore former forest lands. 

Grazing: Clearing of forest for production of cattle has a 200 yearhistory in Hawai‘i. Cattle, being large ungulates, have the samedamaging effects on native vegetation as other ungulates,and the devastating effects of cattle in Hawai'i have been welldocumented. Today, there remain large private ranches, several ofwhich occur within native ecological systems. Ranching-relatedloss of native ecosystems is active in the Kona conservation area inparticular.