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Many Australian natives prove drought resistant

July 20, 2014 - 12:05am

What do Australia, New Caledonia and Hawaii have in common? Australia and New Caledonia are thought to be part of the great continent known as Gondwanaland and hold some of the most ancient species of plants and animals known today. 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 drought tolerant.

Waterwise gardening starts with planting drought tolerant plants. Many Australian native plants fit this bill. Along with Hawaiian native plants, they can help us cut our water bill.

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 as well. 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 local environment. Some of these can grow where nothing else will.

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

Australia is a vast and ancient continent. This isolated land mass still contains some lifeforms that became extinct on other continents eons ago. 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 paperbark tree. It has long been used here in windbreaks. It, like the eucalyptus, is closely related to our native ohia. Our native honey creepers actually feed on the necter of these trees like they do the ohia. I don’t usually recommend the paperbark because it is so common and the flower smell is reminiscent of cooking mashed potatoes. However, there are scores of other species, some with lavender, pink, yellow or red flowers. They vary from bushes to tall trees. My favorite has the form of a weeping willow.

In some tropical countries, paperbark is planted for reforestation purposes since it has some commercial use. The common paperback is well behaved in Hawaii, but in the Florida Everglades, it has done too well because of the draining of that region. This creates an ecological vacuum that the paperbark trees found ideal. Now, instead of sawgrass, some areas are forested with paperback.

The colorful bottlebrushes also include Callistemons. Dozens of species are available in Australian nurseries varying from small evergreen shrubs to large trees. Their flowers are made up 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, which look like beads pressed into the bark of the stem.

Advantages of the bottlebrushes are their insect and disease resistance, tolerance of drought and wet conditions and overall attractive appearance. Some species like the weeping bottlebrush, Callistemon viminalis, bloom most of the year, and are also 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 all along our beaches. One of its main advantages is that it protects other more tender plants from strong salt-laden winds. Again, there are many interesting species. My favorite comes from 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, Brassaia actinophylla, macadamia nut tree, silk oak, banksias, acacias, Australian fire wheel, Stenocarupus, and Australian flame tree, Brachychiton. Many Australian Livistona palm species and cycads have been introduced as well.

Although we have a number of Australian immigrants in our gardens, we have 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 and 500 species of acacia. There are also 57 species of palms.

Many of these unusual and interesting plants should find homes in Hawaii especially as we begin to landscape in areas like South Kohala, Ka‘u, West Molokai, Lanai and even Kahoolawe where original vegetation has been destroyed and conditions are hostile. Of course, like all new introductions we need to be careful that they will not become a problem. Ones like the Queensland umbrella tree and Australian pine have become naturalized in some areas because they are too happy. Cycads and most palms do not naturalize readily. The Alexandra palm is certainly one exception, but these were established in areas where native forests were cleared or damaged.

Even though New Caledonia was once connected to Australia, it must have been many millions of years ago, because plant life there is very different. So little is known about plant species there that palm people are exploring for species not yet found in Hawaii. One that has been introduced and shows great promise is the Chambeyronia from New Caledonia. It is beginning to show up in our gardens with bright red leaves.

This information is supplied by the University of Hawaii College of Tropical Agriculture and Human Resources.

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