Sunday | April 30, 2017
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Tropical Gardening: What comes next after rapid ohia death?

Rapid ohia death appears to be a relatively new fungus disease in Hawaii and is killing trees by the thousands.

The question is, what will our forests look like in 30 years or more with the vacuum created?

If we look back at the time the first humans arrived almost 2,000 years ago, our forests were very different. Vast Pritchardia palm forests covered the highlands and the lowlands. No one knows how many species were present. Today 24 species remain and they are rare in the wild because of rats and pigs eating most seed produced.

The old palms died with few young ones to replace them. When it comes to ohia, we have had big dieouts in the past, but none so potentially devastating as ROD.

What will replace our beloved trees?

As important as our forests are, will we even have forests?

The answer is most likely yes, but they probably will be pioneer species from other parts of the world.

For example, lets look at what Australia and Hawaii have in common.

Australia is thought to be part of the great continent known as Gondwanaland and has some of the most ancient species of plants and animals known today. Many ancestors of these species survived the great extinctions that occurred millions of years ago. Surprisingly, even though Hawaii is about the youngest real estate around, the ancient species thus far introduced prove to be very hardy.

Many are found to be extremely tolerant of our climate zones. Along with native Hawaiian plants and Polynesian introductions, they can help us cut our landscape water bill in the arid parts of the island and also be used to reforest where ohia have died.

Remember, native or non-native, trees fulfill the role of producing oxygen, reducing carbon dioxide by sequestering carbon and helping reduce pollution and soil erosion.

If we are to continue to have forests and viable Hawaiian landscapes we will need to recognize they will be very different than in the past. Nature will replace ohia with other pioneer species with or without human intervention.

It seems that all life has cycles. Ideas, attitudes and philosophies have cycles as well. We shift from conservative to liberal and back. Clothing styles cycle. Even landscape design and plant popularity has cycles.

Often, these swings of the pendulum hit an extreme before a movement back in the other direction. In plant use, we are swinging toward using local, native plants, and a few landscape designers are using only native plants. This is exciting since native plants have been ignored for a long time.

It is important to protect and use our native plants in the landscape and at the same time be on the lookout for rare, beautiful and possibly endangered plants such as those from Australia to enhance our islands’ environment. Some of these can grow where little else will.

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Hawaii is well-known for its varied and unusual plant life. Many plants were introduced from the West Indies, South America and Africa. But few plants adapted themselves as well as those from tropical and subtropical Australia.

Australia is a vast and ancient continent. In some respects, it is the closest to the fabled “lost continent,” where the ancestors of the dinosaur era still roam.

It is a fact that this isolated land mass still contains some life forms that became extinct on other continents eons ago.

And it is not surprising that many plants from Australia adapt well to the Hawaiian Islands. With every climactic zone imaginable in Australia, plus an extremely long period of evolution, there are hundreds of species we can grow here. Less than 1 percent has been introduced.

Take for example the genus Melaleuca. Like the eucalyptus, paperbark, bottlebrushes, allspice, Mountain Apple and guava, it is closely related to our native ohia. Our endemic honeycreepers actually feed on the nectar of these trees like they do the ohia.

Paperbark, or Melaleuca leucadendron, is not recommended to plant because of its tendency to naturalize in marshy area. However, there are scores of other Melaleuca species, some with lavender, pink, yellow or red flowers. They vary from bushes to tall trees. One favorite has the form of a weeping willow.

The colorful bottlebrushes also include Callistemons. Dozens of species are available in Australian nurseries, varying from small evergreen shrubs to large trees. Their flowers consist of clusters of stems that look like the common kitchen bottle cleaner. Flowers vary from white and yellow to pink and red. They are followed by woody seed capsules that look like beads pressed into the bark of the stem.

Advantages of the bottlebrushes are their insect and disease resistance, their tolerance of drought and wet conditions and their overall attractive appearance. Some species such as the weeping bottlebrush, or Callistemon viminalis, bloom most of the year and also are a source of nectar for our native honeycreepers.

Another Australian tree we take for granted in our Hawaiian landscape is the Casuarina, or Australian pine. Named after the Cassowary bird, this primitive tree is not a pine at all.

Our most common species, Casuarina equisitifolia, is extremely salt tolerant and grows along our beaches. One of its main advantages is that it protects other more tender plants from the strong salt-laden winds.

Again, there are many interesting species.

A favorite actually comes from the adjacent island of New Guinea. It is Casuarina papuana, with a broad weeping habit. In the garden, it usually grows to about 20 feet. It can only be propagated by vegetative cuttings here, since it does not form fertile seed.

In Hawaiian gardens, you will find such common Australians as the Queensland umbrella tree, or Brassaia actinophylla; macadamia nut tree; silky oak; Banksia; Acacia; Australian fire wheel, or Stenocarupus; and Australian flame tree, or Brachychiton.

The palm so common to the windward sides of our islands is the Alexandra palm, or Archontophoenix alexanda, and also is from the land of OZ. Many Australian Livistona palm species and cycads also have been introduced.

One thought to be extinct but rediscovered is the foxtail palm, or Wodyetia bifurcate. Since its introduction to Hawaii, it has become one of the most popular in modern landscapes.

Although we have a number of Australian immigrants in our gardens, we’ve barely scratched the surface when it comes to the potential. There are more than 500 species of eucalyptus, 200 species of Grevillea, 100 species of bottlebrushes (Callistemon and Melaleuca) and 500 species of Acacia. There also are 57 species of palms.

Many of these unusual and interesting plants might find homes in Hawaii, especially as we begin to landscape in areas such as South Kohala, Ka‘u, West Molokai, Lanai and even Kahoolawe, where original vegetation was destroyed and conditions are hostile.

Of course, like all new introductions, we need to be careful they do not become a problem. Those such as the Queensland umbrella tree and Australian pine have naturalized in some areas because they are too happy here. Cycads and most palms do not naturalize readily.

The Alexandra palm is certainly one exception, but it got established in areas where native forests were cleared or damaged.

Whatever the future might bring to Hawaiian forests and gardens, we can be assured it will be very different than what we see today. The important thing is that Hawaii remains clean, green and beautiful.

 

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