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Treeferns — remnants of a lost world

February 16, 2014 - 12:05am

Tree ferns were around when dinosaurs roamed the planet. Now remnants of these remarkable plants are primarily found in cloud forests and rain forests that are quickly disappearing. In Hawaii, the endemic tree ferns, commonly called hapuu, are losing the battle to climate change and human activity. A common mistake made in Hawaii is to attempt to grow plant materials where they are not well adapted. This is complicated with weather changes occurring not only with melting glaciers in the Arctic or typhoons in the Philippines but with extensive drought conditions here at home. Statewide, we are getting progressively drier conditions with occasional wet spells, but tree ferns like a consistent supply of moisture. Last year, East Hawaii rivers all but dried to a trickle and in West Hawaii, some areas of drought tolerant kiawe, ohia and haole koa were stressed and dying. In the cloud forests of Kaloko Mauka, and other areas, our hapuu tree ferns — some more than 100 years old — were withering and dying. This year some well-timed rains are helping, but with global warming, extreme droughts separated by stronger storms are expected to become more common.

For many years, it has been common practice to go to the island’s rain forests and cut down hapuu for instant landscaping, or chip it for orchid media. These slow-growing ferns are threatened since they grow only 2 to 3 inches of trunk per year. When removed from the forest, weeds often take over the area. In Kaloko Mauka, 20 years ago, tree ferns covered most of the roadside from the highway to the top of Kaloko Drive. Today, invading grasses are encroaching where people have cut, bulldozed or allowed grazing animals access to the hapuu stands.

The Hawaiian tree fern, hapuu, or Cibotium glaucum, is one of more than 800 species of tree ferns found worldwide. It is native to most high or mountainous islands in Hawaii and found in semi-wet to wet forests from sea level to 5,000 feet elevation.

Hapuu was very common in the wetter areas of all the major islands, but exploitation and drier conditions caused by climate change have reduced the stands drastically. Pulu was used in ancient times for dressing wounds and embalming. Pulu has been used for stuffing pillows and mattresses. Until recently, large numbers were cut for orchid media and landscape use. Trunks cut and planted in less than ideal locations live for a while, then gradually decline and die, thus requiring frequent replacement.

All tree ferns are considered threatened since most species are found in the rapidly diminishing rain forests and cloud forests of the world. It is illegal to ship tree ferns or tree fern products internationally. This does not protect tree ferns within a country from destruction.

The last remaining large stands of hapuu are found primarily on Hawaii Island, however these are being rapidly reduced by clearing and development except in protected areas such as Hawaii Volcanoes National Park.

The leaves of hapuu ii, another less common native endemic Hawaiian tree fern, sport a thick growth of stiff, blackish hair on the petiole. This native tree fern is also slightly taller and has stiffer fronds. Otherwise, the two species of hapuu are similar in appearance. Hapuu ii seldom survives transplanting and is rarely used in the landscape. Unfortunately, some big nursery outlets are selling hapuu and hapuu ii. Most do not survive long after planting in places where they do not get sufficient moisture. Where adapted, tree ferns are excellent as small trees. They are especially pleasing as a specimen to create a tropical effect in the landscape or garden.

The Hawaiian tree fern is becoming scarce and should only be planted where conditions are ideal — wet areas with well-distributed rainfall. Do not remove hapuu from the forest without proper authority. It would be better to landscape with more drought resistant trees and shrubs. Many species of tree fern are relatively easy to grow and reasonably tolerant of a variety of conditions. However, few are presently available in the nursery trade. The common Australian tree fern, Cyathea cooperi, was at one time readily available but is now on the list of invasive species. At least 14 other Australian and New Zealand species are possible substitutes. C. brentwoodi, Puerto Rican tree fern, Costa Rican, New Zealand and Fiji tree ferns are found in some botanical gardens but are not usually propagated. If you are fortunate enough to get one of these species, give it a try in your garden. They prefer well-drained soil in partial shade, but will tolerate full sun in cloudy, mauka areas or in well-watered landscapes. Tree ferns will need protection from the sun and drying winds in hot, sunny lowlands. They prefer slightly acid soil. Tree ferns benefit from a steady supply of water with good drainage. Fertilize occasionally with light applications of a complete fertilizer containing slow-release nitrogen. Avoid quick release chemical fertilizers since they may actually burn the fern. Prune out old and injured fronds, as necessary.

Insects and diseases are few. If you are interested in propagation, the side shoots can be removed to produce new plants. Tree ferns may also be started by spores, but this takes patience and time. Hopefully, some folks in the nursery and landscape business will begin to carry some of these rare beauties. If you are interested in a source of spores with which to experiment, contact me at 325-6440.

This information is supplied by the University of Hawaii College of Tropical Agriculture and Human Resources. For more information on fern culture contact the office near you.