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Hawaii tropical dry forests

Tropical dry forests of Hawaii typically occurred on the leeward side of the main islands and once covered the summit regions of the smaller islands. Most native lowland forests of Hawaii are either seasonal or sclerophyllous to some degree (Sohmer and Gon 1996), and more mesic transition forests occur where conditions are favorable. These transition forests include mixed mesic forests that often contain patches and elements of dry forest communities.

  • Scientific Code
    (OC0202)
  • Ecoregion Category
    Oceania
  • Size
    2,500 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Biological Distinctiveness
Dry forests vary from closed to open canopied forests, can exceed 20 m in height in montane habitats, and are dominated by the tree genera Acacia, Chamaesyce, Metrosideros, Sapindus, Sophora, Pritchardia, Pandanus, Diospyros, Nestegis, Erythrina, and Santalum. (Sohmer and Gon 1996). Dry forests harbor a number of specialist species including native hibiscus trees of the genus Hibiscadelphus, Kokia cookei, Caesalpinia kauaiense, and Santalum paniculatum, and several rare endemics such as Gouania, now represented by only a few individuals (Sohmer and Gustafson 1987, Cuddihy and Stone 1990). Around 22 percent of native Hawaiian plant species occur within this ecoregion, with lower habitat type endemism than tropical moist forests (Sohmer and Gustafson 1987). The palila (Psittirostra bailleui), an endangered finchlike bird, specializes on mamane trees that occur in dry forest habitats (Noss and Peters 1996). Several shrubland, grassland, and herbaceous formations occur within this ecoregion (Sohmer and Gon 1996). Lower Hawaiian dry forest was habitat for several forest birds, such as honeycreepers, fly catchers, flightless rails, other flightless birds (now extinct), and the Hawaiian owl (Asio flammeus sandwicensis).

Conservation Status

Habitat Loss
Tropical dry forests are globally threatened, and Hawaiian dry forests have been reduced by 90 percent (Noss and Peters 1996). Clearing and burning of lowland dry forests began with arrival of Polynesians and the last remnants are being destroyed today through development, expansion of agriculture and pasture, and burning. Most larger fragments of relatively intact dry forests are in montane areas.

Remaining Blocks of Habitat
A few relictual areas survive such as Pu’u Wa’awa’a on Hawai’i, Pu’u o Kali on Maui, Auwahi on Maui, Kanepu’u on Lana’i, and small stands (a few thousand square meters) in the Wai'anae mountains of O'ahu that is currently surrounded by burned slopes or alien-dominated vegetation. Several other important dry forest conservation sites identified by Sohmer and Gon (1996) include the Na Pali Coast of Kaua'i, East Moloka'i Mountains, West Maui Mountains, Leeward East Maui, Lana'ihale-Kanepu'u of Lana'i, and the Kona Subregion of Hawai'i.

Degree of Fragmentation
What little habitat that remains is highly fragmented.

Degree of Protection
Remaining transition forests and dry forests are poorly represented in the existing protected areas system. Strong protection and active management of the remaining remnants of Hawaiian dry forests are needed. Research on effective restoration methods is needed.

Types and Severity of Threats
Introduced plant species are widespread and dense growth and competition for resources prevents the establishment of native plant seedlings. The African fountain grass (Pennisetum setaceum), the shrub Lantana camara, and molasses grass (Melinis minutiflora) are among the major problem species. Introduced rats, plants, and seed-boring insects, grazing by domestic livestock and introduced deer, goats, and pigs, as well as recurring fires inhibit almost any regeneration of native species in most altered habitats.

Suite of Priority Activities to Enhance Biodiversity Conservation

Conservation Partners

•The Nature Conservancy
•The Nature Conservancy of Hawaii
•Hawaii Natural Heritage Program
Relationship to other classification schemes
The Hawaiin dry forest corresponds to Küchler’s (1985) units 1 (Sclerophyllous forest, shrubland, grassland), 5 (Koa forest), and 6 (Koa-mamani parkland). Omernik (1995) did not classify Hawaii, and Bailey (1994) clumped all of Hawaii into one unit.

Prepared by: S. Gon and D. Olson

 

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