page_title: Kohala (mountain)
section_title: Ecology
hierarchical_section_title: Kohala (mountain) / Ecology
caption_attribution_description: English: The native wet forests of Kohala Mountain are multi-layered, diverse ecosystems
context_page_description: Kohala is the oldest of five volcanoes that make up the island of Hawaii. Kohala is an estimated one million years old—so old that it experienced, and recorded, the reversal of earth's magnetic field 780,000 years ago. It is believed to have breached sea level more than 500,000 years ago and to have last erupted 120,000 years ago. Kohala is 606 km² in area and 14,000 km³ in volume, and thus constitutes just under 6% of the island of Hawaii.
  Kohala is a shield volcano cut by multiple deep gorges, which are the product of thousands of years of erosion. Unlike the typical symmetry of other Hawaiian volcanoes, Kohala is shaped like a foot. Toward the end of its shield-building stage 250,000 to 300,000 years ago, a landslide destroyed the northeast flank of the volcano, reducing its height by over 1,000 m and traveling 130 km across the sea floor. This huge landslide may be partially responsible for the volcano's foot-like shape. Marine fossils have been found on the flank of the volcano, far too high to have been deposited by standard ocean waves. Analysis indicated that the fossils had been deposited by a massive tsunami approximately 120,000 years ago.
context_section_description: The natural habitats in the Kohala district range across a wide rainfall gradient in a very short distance—from less than 5 in (130 mm) a year on the coast near Kawaihae, to more than 150 in (3,800 mm) a year near the summit of Kohala Mountain, a distance of just 11 mi (18 km). At the coast are remnants of dry forests, and near the summit lies a cloud forest, a type of rainforest that obtains much of its moisture from "cloud drip" in addition to precipitation. These large cloud forests dominate its slopes. This biome is rare, and contains a disproportionate percentage of the world's rare and endemic species. The soil at Kohala is nitrogen-rich, facilitating root growth.
  The forest lies perpendicular to the prevailing trade winds, a characteristic that leads to frequent cloud formation and abundant rainfall. Thus the rain forests carpeting Kohala are vital to the supply of groundwater on the island. The role of Kohala's ecosystem in supporting water flow has long been recognized. As early as 1902, US Forester E. M. Griffith wrote "Forest protection means not only increasing the rainfall, but more important still, conserving the water supply. The future welfare and agricultural prosperity of the Hawaiian Islands depends upon the preservation of the forest."
  Before humans arrived, the wildlife population at Kohala and on the rest of the island was isolated from other species, as it was separated from the nearest major landmass by over 2,000 mi (3,200 km) of open water. The early colonizers of Kohala came by wind, storm or floating on the ocean. Successful colonizations occur on the magnitude of once every 35,000 years. The 2,000 successful ancestors that arrived at Kohala evolved into about 8,500 to 12,500 unique species, resulting in a very high ratio of the species present being found nowhere else on Earth. Only about 2.5% of the world's rainforest is cloud rainforest, making it a unique habitat as well.
  The mountain supports approximately 155 native species of vertebrates, crustaceans, mollusks, and plants. A diverse complexion of fungi, liverwort, and mosses further add to the variety. In fact, up to a quarter of the plants in the forest are mosses and ferns. These work to capture the water from clouds, in turn providing microhabitats for invertebrates and amphibians, and their predators. Estimates on the water capacity of the forest range from 320 to 1,600 US gal/acre (3,000 to 15,000 L/ha).
  The mountain is also home to several bogs, which exist as breaks in the cloud forests. It is believed that bogs form in low-lying areas where clay in the soil prevents proper water drainage, resulting in an accumulation of water that impedes the root systems of woody plants. Kohala's bogs are characterized by sedges, mosses of the genus Sphagnum, and oha wai, native members of the bellflower family. Other habitats include rain forest and mesophytic (wet) forests.
  The same isolation that produced Kohala's unique ecosystem also makes it very vulnerable to invasive species. Alien plants and feral animals are among the greatest threats to the local ecology. Plants like the kahili ginger (Hedychium gardnerianum) and the strawberry guava (Psidium cattleinum) displace native species. Prior to human settlement, many major organisms such as conifers and rodents never made it onto the island, so the ecosystem never developed defenses against them, leaving Hawaii vulnerable to damage by hoofed animals, rodents, and predation.
  Kohala's native Hawaiian rain forest has a thick layer of ferns and mosses carpeting the floor, which act as sponges, absorbing water from rain and passing much of it through to the groundwater in aquifers below; when feral animals like pigs trample the covering, the forest loses its ability to hold in water effectively, and instead of recharging the aquifer, it results in a severe loss of topsoil, much of which ends up being dumped by streams into the ocean.
caption: The multi-storied canopy of a native wet forest on Kohala Mountain.
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