Hawaiian tropical moist forests

• Category: Forest Biomes.
• Geographic Location: Pacific Ocean.
• Summary: Hawaiian tropical moist forests are known for their volcanic soils, biodiversity, rich vegetation, and large numbers of endemic species.

Hawaii's tropical moist forests are found within the state of Hawaii in the North Pacific Ocean, or Oceania zone, covering close to 3,000 square miles (7,770 square kilometers) of the Hawaiian archipelago. They are within the ecoregion type of tropical and subtropical moist broadleaf forests. The relatively fertile volcanic soil and abundant rainfall together support biodiverse tropical moist forests featuring large numbers of endemic species (those found nowhere else on the planet).

Hawaii contains a variety of forest types at all elevations, with forest cover representing approximately 1.7 million acres (687,966 hectares), or 41 percent of the state's land. Tropical moist forests are located on the windward or northeastern sides of the islands, where abundant rainfall occurs as the trade winds cross the mountains. Trade winds also serve as a moderating influence on the region's warm temperatures. Although these forests have escaped the more extensive deforestation found at lower elevations within the Hawaiian Islands, conservationists consider this forest ecosystem to be endangered.

Hawaii is comprised of 137 islands of volcanic origin. The main Hawaiian Islands include Kauai, Oahu, Molokai, Lanai, Maui, and Hawaii. The state contains numerous climate zones; it is one of the very few U.S. states with a climate suitable for supporting rainforests. The climate zones here support numerous habitats that are renowned for their biodiversity. Hawaii tropical moist forests are among the three major habitat areas comprising the islands, as designated by the World Wildlife Fund, alongside Hawaii tropical dry forests and Hawaii tropical grasslands, savannas, and shrublands. Most of the tropical moist forests are located in the upper elevations within the mountains. Tropical moist forests are further divided into five ecological components: Lowland Wet, Lowland Mesic, Montane Wet, Montane Mesic, and Wet Cliffs.

Upland tropical moist forests are vital components of the state's watersheds, helping provide freshwater to the islands by absorbing moisture and feeding into underground and groundwater sources. The forests also help keep the water clean and are an important defense against soil erosion. Containment of development to lower levels and overall watershed protection has resulted in greater maintenance of biodiversity and native species at higher elevations. Protected areas within the ecosystem include the Alakai Swamp on the island of Kauai and the 'Ola'a Rainforest within Hawaii Volcanoes National Park and Akaka Falls State Park, both on the main island of Hawaii. The ecosystem also houses what is generally regarded as the wettest place on Earth: Mount Waialeale on the island of Kauai.

Biodiversity

Hawaii's isolated existence within the vast Pacific Ocean throughout many centuries has resulted in the development of diverse tropical habitats with a variety of endemic flora and fauna. While exotic, or invasive, species have come to dominate the lower elevations, higher-elevation tropical moist forests still feature more than 90 percent unique endemic species. There is also biodiversity among the individual Hawaiian islands, with each island housing unique species. Common trees include o'hia (Metrosideros polymorpha) and koa (Acacia koa). Plants include tropical fruits and vegetables, shrubs, fungi, mosses, vines, orchids, and ferns. Trees and vines dominate the forest canopy, while the forest floor consists of a spongy layer of decaying ferns, mosses, and other organic matter. The tropical moist forests also contain bogs featuring sedges, grasses, ferns, shrubs, and small trees.

Animals include a variety of snail, invertebrate, bird, and insect species, including more than one-third of the world's known species of fruit flies. Known species unique to the islands include Hawaiian land snails, Hawaiian lobelias, Eupithecia moths, and Hawaiian honeycreepers, the latter of which are among its unique native bird species. The ecosystem is also home to one of Hawaii's native mammals: the Hawaiian hoary bat or 'ope'ape'a (Lasiurus cinereus semotus). Exotic animal species present in the forests include the destructive feral pig. Many of Hawaii's endangered native species of flora and fauna live within tropical moist forest areas such as the Alakai Swamp.

Human Settlement

Polynesians were among the first humans to settle Hawaii, arriving on the islands more than 1,500 years ago. The indigenous Hawaiian culture that developed placed strong emphasis on living in harmony with the natural world. Captain James Cook was among the first Europeans to arrive when he landed in 1778, beginning a period of heavy immigration to the islands and the concomitant introduction of non-native flora and fauna.

Exotic animal species introduced into the islands have included pigs, dogs, cattle, sheep, goats, cats, rats, mongoose, and a variety of birds and plants. In the twentieth and twenty-first centuries, population growth, widespread development, and military training activities in the lowlands have resulted in deforestation and accelerated loss of native habitats and species. Other modern concerns include the state's reliance on the tourism industry and its environmental effects.

Environmental Threats

Significant threats to Hawaii's forests have included widespread deforestation at lower elevations; land development for residential, agricultural, and military uses; habitat loss; disease; the introduction of invasive nonnative species such as feral pigs; and tourism and recreational activities. Approximately two-thirds of the original forest cover has been lost. Much of the highland tropical moist forests remain, while many of the lowland and foothill moist forests have been lost to deforestation.

Some of the lowland forests regenerated, but these new forests are largely populated with nonnative species. Hawaii is home to the highest number of endangered species of any U.S. state, containing about 40 percent of the world's threatened population. Extinct or endangered species include land snails, native forest birds, and the hoary bat, as well as almost 400 varieties of plants.

The potential impacts of climate change are still being studied. Carbon storage in the soil and vegetation remains in delicate balance, and it is likely that rising carbon dioxide levels in the atmosphere will have some type of impact, but effects on the Hawaiian Tropical Moist Forests biome are not well understood.

Climate change has altered how moist forests are, so drier conditions coupled with strong winds pose environmental threats to the island chain. In 2023, the island of Maui suffered from a massive wildfire, known as the Lahaina fire, caused by broken power lines that sparked a fire in dry vegetation. Furthermore, strong winds from Hurricane Dora, which was hundreds of miles south of Maui, pushed the fires toward the coastline extremely quickly. Around 3,200 acres (1,294 hectares) were burned. Ramifications of such an event include the demolition of thousands of plants, trees, animals, and insects along with the potential spread of invasive species and the potential for harmful dusts to remain for months to follow.

Conservation Efforts

Protection and restoration efforts within Hawaii's tropical moist forests have included the removal of exotic species such as feral pigs, and land-use zoning. State efforts include the creation of watershed partnerships, an agreement between state, federal, and private landowners to manage forest resources in a sustainable manner designed to protect the vital forest watershed. Watershed protection has been a key avenue of forest preservation in the highland tropical moist forests. The state Forest Stewardship Program is among several measures designed to encourage responsible forest management. Organizations and agencies involved in conservation and restoration efforts include the World Wildlife Fund, various US federal government agencies, and the Hawaii Department of Land and Natural Resources.

Many of Hawaii's highlands are zoned for conservation; some feature national parks and other protected wilderness areas. Protected areas within Hawaii's tropical moist forests include Hawaii Volcanoes National Park, the Hawaiian Islands Biosphere Reserve, the Kalaupapa National Historic Site, Kaloko–Honokohau National Historical Park, and Pu'uohonua O Honaunau National Historical Park. The state's Natural Area Reserves System includes tropical moist forest areas. A conservation district encompasses many of the remaining natural areas dominated by native species, but others are left unprotected.

Bibliography

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Cheng, Martha. “Hawai'i's Endangered and Threatened Species.” HONOLULU Magazine, 1 May 2024, www.honolulumagazine.com/hawaii-endangered-threatened-species/. Accessed 23 Oct. 2024.

Culliney, John L. Islands in a Far Sea: The Fate of Nature in Hawaii. University of Hawaii Press, 2006.

Department of Natural Resources and Environmental Management. “Impact of Rising Temperature on Terrestrial Carbon Flux, Partitioning, and Storage in Tropical Wet Forests.” College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. 2012. . Accessed 23 Oct. 2024.

“Division of Forestry and Wildlife: Native Ecosystems Protection & Management - Rare Plant Program.” Department of Land and Natural Resources, dlnr.hawaii.gov/ecosystems/rare-plants/. Accessed 23 Oct. 2024.

“Preliminary After-Action Report: 2023 Maui Wildfire.” U.S. Fire Administration, 8 Feb. 2024, www.usfa.fema.gov/blog/preliminary-after-action-report-2023-maui-wildfire/. Accessed 23 Oct. 2024.

Ricketts, T. H., E. Dinerstein, D. M. Olson, C. J. Loucks, et al. Terrestrial Ecoregions of North America: A Conservation Assessment. Island Press, 1999.

Ziegler, Alan C. Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press, 2002.