Rapid ohia death appears to be a relatively new fungus disease in Hawaii and is killing trees all over the Islands. But with heavy rains and unusually warm weather in West Hawaii, we are seeing a new disease attacking our ohia. This fungus attacks the leaves and causes premature leaf drop. It is similar to the disease that killed most Rose Apple trees in East Hawaii. This is a close relative of the ohia and guava. If the weather continues to warm, it is likely we will see more diseases in the normally cool areas of the islands. For example in Kaloko Mauka, we are seeing fungus diseases attacking palms like the Howea forsteriana that did quite well until the recent warming trend.
The question is what will our forests look like in thirty 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 alike. No one knows how many species were present. Today 24 species remain and they are rare in the wild due to 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 die outs 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 will probably 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 Gondwana land and holds 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 Australian species thus far introduced prove to be very hardy. Many are found to be extremely tolerant of our wet to dry conditions. Along with Hawaiian native plants and Polynesian introductions, they can help us cut our landscape water bill in the arid parts of the island. They can also be utilized 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 to 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 may 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 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 utilize 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 little else will.
Hawaii is well known for its varied and unusual plant life both native and nonnative. 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. 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. 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 one 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 due to 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 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. Advantages of the bottlebrushes are their insect and disease resistance, their tolerance of drought and wet conditions, and their overall attractive appearance. Some species like the weeping bottlebrush or Callistemon viminalis, bloom most of the year, and are also a source of nectar for our native honeycreepers.
In Hawaiian gardens, you will find such common Australians as the Queensland umbrella tree, Brassaia actinophylla, macadamia nut tree, silky oak, banksias, acacias, 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 is also from the land of Oz. Many Australian Livistona palm species and cycads have been introduced as well. 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 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 (Callistemon and Melaleuca), and 500 species of acacia. There are also 57 species of palms.
Many of these unusual and interesting plants may 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 here! Cycads and most palms do not naturalize readily. The Alexandra palm is certainly one exception, but these got established in areas where native forests were cleared or damaged.
Whatever the future may bring to Hawaiian forests and gardens, we can be assured that it will be very different than what we see today. The important thing is that Hawaii remains “Clean, Green and Beautiful.” This great motto is memorialized by the Outdoor Circle that continues to play an important role in keeping Hawaii from becoming the concrete and asphalt blight which plagues so many urbanized parts of the mainland.