Tree ferns suffer from continued drought


By NORMAN BEZONA

University of Hawaii at Manoa College of Tropical Agriculture and Human Resources

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.

Last year was a dry year and this year has been even worse. Statewide, it is one of the driest years in over a century of keeping records. In East Hawaii, rivers have all but dried to a trickle and in West Hawaii, the drought tolerant kiawe and haole koa appear all but dead. In the cloud forests of upper Kona like Kaloko Mauka, our hapu‘u tree ferns are withering and dying. Some are well over one hundred years old.

Speaking of tree ferns, this is an example of plants often used in the wrong place. For many years, it has been common practice to go to the rainforests of our islands and cut down hapu’u for instant landscaping, or chipped for orchid media.

Today, these beautiful ferns are threatened because they are very slow growing, and in most areas, grow only 2 to 3 inches of trunk per year. When removed from the forest, weeds often take over the area exposed. An example is in Kaloko Mauka, Kona where the tree ferns 20 years ago covered most of the roadsides from the Belt Highway to the top of Kaloko Drive. Today, invading weeds are encroaching where people have illegally cut down the hapu’u, bulldozed or allowed grazing animals access to the hapu’u stands.

The scientific name of our common tree fern is Cibotium glaucum. The common name is hapu‘u or Hawaiian tree fern. This is one of more than 800 species of tree ferns found worldwide.

They are native to most high or mountainous islands in Hawaii. These descendants of an ancient type of vegetation are found in semi-wet to wet forests from sea level to 5,000 feet in elevation.

Hapu‘u was very common in the wetter areas of all the major islands, but over exploitation and drying conditions due to climate change have reduced the stands drastically. Pulu was used in ancient times for dressing wounds and for 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.

Presently all tree ferns are considered threatened since most species are found in the rapidly diminishing rainforests 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 hapu‘u are found primarily on the Island of Hawaii, however these are being rapidly reduced by clearing and development except in protected areas such as the Hawaii Volcanoes National Park.

The leaves of hapu‘u i‘i, another less-common native 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 hapu‘u are similar in appearance. Hapu‘u i‘i seldom survives transplanting and is rarely used in the landscape.

Tree ferns are excellent as small trees. They are especially pleasing as a specimen to create a tropical effect in the landscape or garden.

Unfortunately, the Hawaiian tree fern is becoming scarce, so should only be planted where garden conditions are ideal, such as wetter areas with well distributed rainfall. Do not remove hapu‘u from the forest without proper authority. Because our islands seem to be getting dryer, it would be better to landscape with more drought resistant trees and shrubs.

There are many species of tree fern that are relatively easy to grow and reasonably tolerant of a variety of conditions.

However, none are presently available in the nursery trade. The Australian Treefern, Cyathea cooperi was at one time readily available but is now on the list of invasive species since it is one of the few that tend to naturalize in some situations.

Others like the Puerto Rican tree fern, Costa Rican 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. Organic sources are preferred. 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. Art Smith of Puna has had success in spore-growing a variety of tree ferns.

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

 

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