Kia‘i Moku: Used in reforestation, albizia now poses threat


Near Kualapuu, Molokai, there are Makahiki and hula grounds. Last year, 850 fast-growing invasive trees covered the platforms, where ancient Hawaiians played games as part of the Makahiki festival, the annual celebration marked by several months of peace, thanksgiving and feasting.

These trees originated from the jungles of the Molucca Islands, 5,000 miles away in Indonesia. The islands are part of the Wallaceae “hot spot,” an area of Indonesia with some of the world’s highest levels of biodiversity, including more than 10,000 plant species and 650 different bird species.

Albizia, or Falcataria moluccana, has at least one trait that gives it an advantage over Hawaii’s native plants. Albizia is a nitrogen-fixing tree; bacteria in albizia roots convert nitrogen from the atmosphere into a form available for the tree. These fertilizer factories built into the roots give albizia an extra boost; albizia can reach 30 feet tall in just two years.

In Hawaii, many soils are nitrogen poor, particularly on new lava flows. Alibizia can establish on these nutrient-poor soils, altering the soil function and structure, and then pave the way for other invasive plants, such as strawberry guava, to invade these areas.

Albizia first were introduced to Hawaii in 1917 for reforestation and as an ornamental. By 1960, about 138,000 trees statewide had been planted, most on Kauai. In Maui County, four were planted on Molokai, and 14 on Maui. These practices were all part of early attempts at watershed protection.

Hawaii foresters and agriculturalists realized the fragility of the watersheds. Native plants were being grazed heavily and roots trampled by cattle. Erosion was increasingly widespread in low-elevation forests.

Fencing to protect areas from cattle was one part of the solution, but foresters felt more needed to be done. In 1851, German botanist William Hillebrand noted the loss of Hawaiian forests and called for action, saying, “Large tracts now lying (in) waste may be speedily covered with forests.”

At the turn of the century, the first territorial governor, Sanford B. Dole, encouraged reforestation efforts as a conservation measure. He felt that some forests would recover with the exclusion of cattle. But for other forests “denuded of trees for a considerable time (and) covered with a heavy growth of grass, artificial assistance is essential to reforesting.” Trees from throughout the world were introduced to preserve forest cover and to prepare for a potential timber industry.

Unfortunately, many of the characteristics that foresters sought in trees to prevent erosion now are recognized as characteristics that make a plant invasive. Hawaii’s native trees are much smaller and slower growing than albizia.

For example, ohia, the predominant native tree of lowland forests where albizia can live, is much slower growing. On areas of Hawaii island, researchers have noticed that when albizia invades an area, 100 percent of the ohia die. The structure and function of forest soils is altered by albizia and a once-diverse native forest is transformed into an alien-dominated ecosystem.

On Molokai, the Molokai/Maui Invasive Species Committee is working to eradicate this invasive tree. All 850 trees were controlled by a small army of field crews from The Nature Conservancy, U.S. Fish and Wildlife Service, state Department of Land and Natural Resources, and the Maui Invasive Species Committee.

In keeping with the site’s cultural significance, cultural advisers performed a blessing in the area, called for support from the site’s ancestors and thanked the trees for the shade and oxygen they had provided, but asked them to go.

The project was both safe and successful. One year later only four trees required another treatment.

Unlike Molokai, albizia on Maui is too widespread to eradicate with current resources. Albizia is an abundant seeder and plants naturally become established in abandoned lands and forests.

You can help prevent its spread and protect native areas by not planting any new trees in your area.

* Lissa Fox is public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University.

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