Wai‘anae Ecological Characterization

Forests and Streams

The Wai‘anae Mountains are older and taller than the mountains of the neighboring Ko‘olau range, and the plants and animals that initially resided there had an evolutionary head start of about 1.5 million years. The formation of the Ko‘olau Mountains dramatically affected the climate and microenvironments of the Wai‘anae Mountains by casting them in a rain shadow. Because the prevailing wind conditions (the trade winds) cause clouds to rise and drop their precipitation on the Ko‘olau Mountains before reaching the Wai‘anae Mountains, the Wai‘anae Mountains receive much less rainfall. The median annual rainfall for the Wai‘anae Mountains varies from 20 to 75 inches, with only the small summit area of Mount Ka‘ala, which is above the rain shadow, receiving the highest amount (for more information, see the Ke a‘o Ulu: Prevailing Conditions section). Relative to the Ko‘olau Mountains, the Wai‘anae Mountains have a greater range of elevations, moisture regimes, and habitat types. As a result, they make up the most biologically diverse region on the island of O‘ahu (USEPA 1996).

Human habitation changed much of the low-lying coastal areas with the introduction of farming and plants like sweet potato, taro, and ti. The sandalwood trade and sugar plantations that came about after Western contact further changed the environment by reducing the forest cover and altering water resources. While much of the lowland and coastal region has been changed by development, the areas most valuable to many remaining native plants and animals are places that are not easily accessible to humans: places like Palikea and Pu‘u Hapapa in the back of Lualualei, Mount Ka‘ala and Kamaile‘unu in Wai‘anae, and Kahanahāiki and ‘Ōhikilolo near Mākua (Makua Implementation Team and others 2003). The Wai‘anae range supports some of the last dry cliff habitat in the islands. It is estimated that native dry land vegetation only remains in about 25 percent of its original range, with a portion of this in the Wai‘anae Mountains (Hawaii Conservation Alliance 2003).

The Wai‘anae Mountains contain over 85 species of sensitive plants, with new populations found every year (Makua Implementation Team and others 2003). They also provide critical habitat for plants and animals like the endangered O‘ahu ‘elepaio (Chasiempis sandwichensis ibidis). Over 16,990 acres are designated as ‘elepaio critical habitat on federal, state, county, and private lands in the Wai‘anae Mountains.

Ka‘ena Point Natural Area Reserve at the northern end of the Wai‘anae Mountains supports endangered plants like ‘akoko (Chamaesyce spp.) and ‘ōhai (Sesbania tomentosa) and recovering populations of birds that are protected by the Migratory Bird Treaty Act, such as the Laysan albatross (Phoebastria immutabilis) and wedge-tailed shearwaters (Puffinus pacificus chlororhynchus). The lack of development and infrastructure in this part of O‘ahu allows the natural beauty of the dry coastal region to remain relatively undisturbed when compared with the developed coastlines to the southeast.

Freshwater streams in Hawai‘i are the link between the coast and the mountains and are a highly valued resource. Preserving healthy streams is critical to protecting native species. Though the majority of streams in the Wai‘anae moku are not perennial at the coast, native species in the upper elevation of the streams rely on marine or estuarine environments for a portion of their life cycle. All of the native fish and crustaceans of Hawai‘i's freshwater systems are amphidromous, meaning they must travel from salt water to fresh water to complete their growth. Alterations to the lower portions of the streams, such as paving drainage canals or routing agricultural runoff into streambeds, can have a devastating effect on the stream water quality and the survival of those native species.

Mount Ka‘ala is the site of a unique montane bog habitat in the moku. The summit is often shrouded in clouds and receives an average of 60 to 80 inches of rain annually. The ground is soft and covered with lapalapa, ‘ōhi‘a, ferns, and mosses. Kaneamimi, Kukaki, Niolopua and Kānewai streams flow from Mount Ka‘ala to Honua Stream in the Wai‘anae Valley (Leeward TLCF Summer Institute 1998b). These streams were once used by the Hawaiians as part of their agricultural terracing system, the ‘auwai, which maximized the precious water resources in the moku.

In 2000, the Hawai‘i Biological Survey and Bishop Museum conducted initial surveys of Wai‘anae moku coastal streams, estuaries, and wetlands. These important areas provide nursery habitat for native fish and insects, listed in the following table.

Native Stream Organisms

Type	Common Name	Species name
Fish	‘o‘opu h‘iukole or ‘o‘opu ‘alamo‘o	Lentipes concolor
Fish	‘o‘opu nōpili	Sicyopterus stimpsoni
Fish	‘o‘opu nākea	Awaeous guamensis
Fish	‘o‘opu naniha	Stenogobius hawaiiensis
Fish	‘o‘opu ‘akupa or ‘o‘opu ‘ōkuhe	Eleotris sandwicensis
Crustacean	‘ōpae kalaole or ‘ōpae kuahiwi	Atyoida bisculata
Crustacean	‘ōpae o‘eha‘a	Macrobrachium grandimanus
Snail	Hīhīwai	Neritina granosa
Snail	Hapawai	Neritina vespertina
Snail	Pīpīwai	Theodoxus cariosus

Source: State of Hawaii DLNR 2004.

References Cited

Hawaii Conservation Alliance. 2003. Conservation of Biological Resources in Hawaii: Baseline and Status Summary for 2003. http://www2.hawaii.edu/scb/docs/library/lib_consReport2003fixed.htm

Leeward Technology Literacy Challenge Fund (TLCF) Summer Institute. 1998b. Kaala Watershed Study Homepage. http://www.k12.hi.us/~waianaeh/TLCF/water/Splash/splash.html

Makua Implementation Team, Will Chee Planning Inc., and Hawaii Natural Heritage Program. 2003. Final Implementation Plan: Makua Military Reservation, Island of Oahu. Prepared for U. S. Army Garrison, Hawaii, Directorate of Public Works, under Contract No. DACA83-96-D-0007.

State of Hawaii Department of Land and Natural Resources (DLNR). 2004. Hawaii's Native Stream Animals. Division of Aquatic Resources. http://www.hawaii.gov/dlnr/dar/streams/stream_natives.htm

U.S. Environmental Protection Agency (USEPA). 1996. "Endangered and threatened wildlife and plants; Determination of endangered status for twenty-five plant species from the Island of Oahu, Hawaii." 61(198). http://www.epa.gov/docs/fedrgstr/EPA-SPECIES/1996/October/Day-10/pr-10264.html

Related References

Englund, R.A., K. Arakaki, D.J. Preston, S.L. Coles, and L.G. Eldredge. 2000. Nonindigenous Freshwater and Estuarine Species Introductions and their Potential to Affect Sport Fishing in the Lower Stream and Estuarine Regions of the South and West Shores of Oahu, Hawaii. Bishop Museum Technical Report No. 17. Prepared for the Hawaii Department of Land and Natural Resources, Division of Aquatic Resources by the Hawaii Biological Survey, Bishop Museum. http://hbs.bishopmuseum.org/pdf/tr-17.pdf

McGrath, E.J., K.M. Brewer, and B. Krauss. 1973. Historic Waianae, A Place of Kings. Island Heritage Limited. Norfolk Island, Australia. http://www.aloha.com/~hoa-aina/history.html

State of Hawaii Department of Land and Natural Resources (DLNR). 2003. Wao Akua: Sacred Source of Life. Division of Forestry & Wildlife. Honolulu, HI.

U.S. Environmental Protection Agency. Undated. Watershed Assessment Tracking & Environmental Results System: Water Quality Inventory for Watershed Oahu. http://oaspub.epa.gov/pls/tmdl/w305b_report.huc?p_huc=20060000&p_state=HI

Wagner, W.L., D.R. Herbst, and S.H. Sohmer. 1999. Manual of the Flowering Plants of Hawaii Revised Edition. University of Hawaii Press and Bishop Museum Press. Honolulu, HI.

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