Tropical Gardening: Hawaii forests and gardens radically altered by diseases, insects and man

The COVID-19 pandemic has clearly made us aware of how our individual lives and even society can be altered in a very short time by disease.

Our forests and landscapes can change rapidly as well. A very warm, wet period or dry one can drastically alter the species makeup of a forest. For example, our ohia forests are suffering not only from rapid ohia death, but also from other diseases.

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Warming weather created ideal conditions for myrtle rust (Austropuccinia psidii) to cause defoliation, dieback and even death of ohia and many other related species in the myrtle family. Most rose apple trees died out during the past decade because of this disease. About 150 species are susceptible, including Mountain Apple, guava, eucalyptus, callistemon, melaleuca and rhododendron.

What happens as these species die? Other species fill the void thus altering forests and even our gardens. Hawaii gardens represent the continuing influence of many diverse cultures creating new experiences.

Destruction, rebirth and evolution continue to happen. We must learn to adapt to change and at the same time keep as many of the good qualities of the past where we can. This remains true as we face the challenges of climate change, population increase causing land use issues and protecting our unique natural resources and culture.

We have a wide variety of plants, native and introduced. By keeping the lush vegetation an integral part of our communities, we actually do our part to fight pollution, global warming and make life more enjoyable.

One of the easiest ways to decrease the carbon dioxide levels in the atmosphere is to plant trees. Among the best are natives such as loulu palms, ohia, hala, wiliwili, hoawa, alahe‘e and a‘ali‘i. Other plants such as the beach and mountain naupaka are attractive to many birds and also make good ornamentals for a garden. Flowers of the ohia, koa, hau, milo and mamane might even attract some native nectar-feeding birds like iiwi, amakihi, apapane and elepaio.

The hala tree is another tree of interest and beauty. It can be grown from sea level to at least 3,000 feet elevation. Lauhala, or leaf of the Pandanus, has probably been used for thousands of years. Not only are the leaves used for walls, floor mats and thatched roofs, today artists weave purses, shopping bags and hats. Even the parts of the fruit were eaten during periods of food shortage. Today, island campers will use the fibrous segments as a toothbrush.

The Pandanus family, closely related to palms, is found throughout the old world tropics. There are hundreds of species, from miniature shrubs to large trees. Most Pandans can be distinguished by their aerial roots. These roots give them the common name of “walking trees.”

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In Hawaii, we have two common native species. The puhala, Pandanus odoratissimus, is found naturally growing along many coastal areas. The mountain ‘ie‘ie, Freycinetia Arnotti, is found climbing vine-like up ohia trees in mauka forests, sometimes 80 feet or more.

Another group of plants to consider are those the Polynesians brought with them such as coconut, kukui, Mountain Apple, banana, sugarcane, bamboo and breadfruit. These include hundreds of varieties and are referred to as canoe plants.

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