Tropical Dry Forests of Hawaii

By Fausto Rendon

and

Zachary Samuels

The state of Hawaii is composed of 132 islands and several reefs. These islands and reefs are located in the Pacific Ocean; just below the Tropic of Cancer. There are 8 main islands on the south side of the chain in which the island of Hawaii is the last. The youngest and largest island, Hawaii, has altitudes up to 4,000 m. The island is comprised of five volcanoes two of which are highly active.

Kanaio Natural Area Reserve is located on East Maui with native dry forest patches occurring on rocky lava substrate.  Although diverse in tree species, this site is more open in canopy cover than other sites.

The formation of the Hawaiian islands began with volcanic eruptions millions of years ago. The younger islands are only several hundred thousand years old. Though initially a volcanic rock, eventually, through erosion and the formation of mud from a mixture of dust and ash was able to support plant life. These simple plants forms include: moss, lichen and ferns.Hawaii’s fragile isolate ecosystem has allowed endemic species of both plants and animals to evolve; including fungi,mosses, snails, birds, and other wildlife. 

The Hawaiian Islands form an archipelago that is the largest in the world, with a length of 2,000 miles, and the oldest.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 (type of vegetation that has hard leaves and short internodes) to some degree. Dry forests vary from closed to open canopied forests, they can exceed 20 m in height in montane habitats. They also harbor a number of specialist species including native hibiscus trees. Furthermore, the lower Hawaiian dry forests were habitat for several forest birds, such as honeycreepers, fly catchers, flightless rails, other flightless birds (now extinct), and the Hawaiian owl. The native dry-land forests were a great source of diverse plant materials used in vessels, implements, food gathering, fishing, shelter, medicines and rituals.

The first inhabitants of the Hawaiian islands were wandering Polynesians that arrived in the islands throughout 2000-800 yrs. BP. By the early 1800's Mariners found their way to the islands and whaling ships were anchored in Hawaiian ports as the islands were now the starting point for the Pacific Ocean whaling industry. Hundreds of ships and thousands of crew brought new money, but they also brought lax social values and disease. First settlers to Hawaii introduced pigs and chickens of Asian ancestry. They also brought sugar cane,coconut, banana, and sweet potato among other plants. The first cattle, originating from California, were introduced by Capt. George Vancouver on his second trip in 1793.After the initial importation, King Kamehameha I placed a taboo on the slaughter of cattle, so that by 1830 when it was removed, cattle were very numerous.

Unfortunately, 90 percent of Hawaii's native dry land forests has been lost due to human activities such as land clearing, wildfires, and the introduction of alien species that have had disruptive and harmful effects.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. Browsing animals and alien grasses have caused significant damage. The introduced grasses are fire-adapted and have increased the incidence of wildfire in the Hawaiian Tropical Dry Forest (which itself is not adapted to fire). Also, the introduced plant species are widespread and dense growth and competition for resources prevents the establishment of native plant seedlings. In addition the non-native feral mammalian herbivores are detrimental to the forests because the native plants are not adapted to them.

The  future of this delicate ecosystem is not set in stone, however it is clear that without any aid the tropical dry forests of Hawaii will succumb to the destructive foreign elements brought  by humans.This includes, agriculture, urban development, ranching and the introduction on invasive species. At this point it is obvious that the inhabited parts of the Hawaiian islands by humans will not be restored; nonetheless, there are pockets of reserves spread though-out the islands that might stand a chance of being preserved in the long run. The preservation of the native Hawaiian dry forests depends on people. First of all Forest Reserves help keep people from further development of the land and therefore help preserve the dry forests. In addition, volunteer groups collect seeds, grow plants and then replant them out in the forest to help promote the growth of native plant species who are now competing with the invasive foreign plants. Some examples of the ways people are helping restore Hawaii’s dry forests  are the Hawai‘i Forest Industry Association and the Hawai’i Forest Institute. The Tropical Dry Forests of Hawaii can never be restored the original prosperity but with the help of people, they can be preserved for future generations.

Replanting of all species on the Federally threatened species (45% of dry forest species) is overseen by federal and state agencies and it is illegal for the general public to outplant these species due to the concern that cultivated varieties will breed with outplanted species and possibly compromise the genetic integrity of species.  However, it is possible to outplant non-threatened species over large areas. . Efforts to conserve dry-land forests in Hawaii are focused mostly on the exclusion of ungulates (through the use of fences) and the removal of invasive plant species. Although important, these activities are not sufficient to reestablish self-sustaining native forests.The goal is to restore natural forest processes which include seed dispersal, seed germination and seeding regeneration.. Volunteer and part-time laborers work to eliminate the invasive grass and other invasive species using both herbicides and hand-pulling. Native tree, shrub, vine and grass species that were elements of the original forest community are outplanted during monthly volunteer trips. By replanting and monitoring the  success rates of replanting, a conclusion of the possible increase the extent of dry forest regions in Hawaii can be drawn..  Furthermore, there is debate concerning the impact of non-native species on native dry forest.  Non-natives are a threat to remaining fragments of dry forest, however, the complete or rapid removal of non-natives plants may have a negative impact on natives species by changing forest structure, microclimate, and disturbance involved with non-native plant removal.  Thus, small scale and large scale experimental plots that remove some or all on the non-native species may provide insight on how to best manage and extend the extent of dry forests.

Works Cited

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