Hawaii is home to many tropical trees, some native and others introduced. Introduced trees hold an important place in Hawaii’s history and mythology, and continue to be economically and culturally important. Native trees are vital members of Hawaii’s ecosystems and continue to support a web of other native species.
The coconut palm (Cocos nucifera), a familiar sight on most of Hawaii’s beaches, is a relative newcomer, brought by early Polynesians for wood, thatch and, to a lesser extent, food. Because of their remoteness, the Hawaiian Islands are one of the only tropical places on earth where coconuts did not reach without human aid. Coconuts have naturalized in Hawaii and spread slowly in low lying coastal areas. Small, naturally occurring, groves of these palms often indicate the presence of underground fresh water springs. Coconut palms require well-drained soil and full sun. They will tolerate wind, salt and drought but grow best when watered regularly.
Milo (Thespesia populnea) is a small tree that grows up to 30 feet high with heart-shaped leaves. Its blossoms, which resemble partially-closed hibiscus flowers, are yellow when they open in the morning but turn deep orange-red to purple by evening. Milo is thought to have been introduced by early Polynesians, who used it for wood, medicine and perhaps religious purposes. Today the tree is widely used in the landscape for shade and windbreaks and is highly valued by woodworkers for its beautiful, dark brown wood. Milo thrives in sunny, coastal locations with well-drained soil, and does best when given moderate amounts of water.
Wet Forest Trees
The native koa tree (Acacia koa) was once widespread in windward forests throughout the islands and is one of Hawaii’s largest native trees. These large hardwoods were used by ancient Hawaiians to make deep-hulled voyaging canoes. Mature koas have yellow, ball shaped flowers and gray-green, sickle-shaped leaves called phyllodes that appear after the true leaves drop. Their roots develop nodules that harbor nitrogen-fixing bacteria to supply added nutrients in Hawaii’s poor volcanic soils. Koas need deep, rich soil, full to partial sun and ample water.
Hawaii’s native mountain sandalwood (Santalum freycinetianum) was harvested almost to extinction during the reign of Kamehameha the Great in the 1800’s, when the common people of Hawaii were forced to harvest these trees for export to China. There are several species of sandalwood native to Hawaii, all valued for their fragrant heart wood. All of these species are believed to be root parasites, which grow in association with other specific host plants. The sandalwood attaches thin roots directly to the roots of their hosts to take up water and nutrients. These trees must be planted near suitable host plants, which include a'ali'i (Dodonea viscosa), koa (Acacia koa) and ohi'a lehua (Metrosideros polymorpha). Mountain sandalwood requires the rich, moist soil and partial shade typical of high elevation, windward locations.
Dry Forest Trees
The wiliwili tree (Erythrina sandwicensis) is endemic to Hawaii and found only in dry forests. These large, deciduous trees with gnarled trunks produce clusters of beautiful flowers colored red, yellow, white or even green. Much of the endangered wiliwilis’ habitat has been altered by grazing and development. Wiliwilis grow well in dry, sunny lowlands with well-drained soils and infrequent irrigation.
The mamane (Sophora chrysophylla) is a shrubby native tree found in dry to mesic forests to sub alpine elevations. Mamane produces pendant clusters of golden yellow pea-like flowers that mature into hard, dry seed pods. Their seeds are the primary food of the endangered native bird called the palilla. Mamane habitat has been severely reduced by grazing and impacts from feral sheep and goats. Fortunately, programs are under way to protect the last mamane habitats. Mamane trees must have full sun and well-drained soil. They thrive in chilly, drier leeward locations above 1,500 feet, but can be grown almost down to sea level with minimal irrigation.