Carol Kwan was just a little nervous when Hurricane Iselle was barrelling toward the islands last month.
The reason: The near-$1 million project she was working on to remove a dozen large albizia trees from Manoa’s Lyon Arboretum was scheduled for the following month, and she knew the massive trees were vulnerable in high wind and rain, putting at risk the scores of rare, endangered and irreplaceable species planted below them.
"I was saying quite a few prayers," said Kwan, a certified arborist and consultant to the project.
As it turns out, Hawaii island took the biggest hit from the Aug. 8 storm, with hundreds of albizia trees having been walloped by tropical storm-force winds in Puna.
Oahu escaped the worst of it, which means the long-awaited tree removal project at the University of Hawaii arboretum will be able to commence in the next few days.
The plan is to remove 12 of the largest albizia trees in the state, a stand situated just mauka of the Great Lawn. University officials want to remove the threat to some of the arboretum’s rarest plants, which are planted under the towering albizias.
The rare and endangered plants include a wide range of palm tree species from islands across the Pacific and at least one from Borneo found nowhere else in the United States. Another vulnerable specimen is the striking flame tree of Trinidad, with its brilliant, torchlike red blooms.
Planted in the arboretum 85 years ago or more, the full-grown albizia trees range in height from 130 feet to 205 feet. The largest has a trunk nearly 11 feet around, officials said.
The albizia, or Falcataria moluccana, is native to the lowlands in the Molucca Islands of Indonesia and was introduced to Hawaii in 1917 by Joseph Rock in an effort by early foresters to save Hawaii’s watersheds. Over the next several decades, thousands of albizia seedlings and seeds were planted throughout the islands, especially on Kauai, Oahu and Hawaii island, and the species has proliferated across the state.
As it turns out, the tree was bad news for the native forest. Because they are nitrogen-fixers and drop prolific leaf litter, they alter the soil chemistry, allowing other weeds to invade and take over native habitats.
Described as the fastest-growing tree in the world, the albizia has a recorded growth rate of up to 15 feet per year. The trees can develop an immense canopy of more than 150 feet in width.
They have weak wood, making them prone to breakage. And the trees have large branches that are exceptionally long, with high weight on the ends. While branch failure is especially common during high wind, these trees are also susceptible to "sudden limb drop" in which branches will drop without warning for no apparent reason, Kwan said.
"They can cause a lot of damage," said Carl Evensen, the arboretum’s interim director.
Pearl City-based Imua Landscaping Co. will perform the tree removal work at a cost of $980,000. Much of the high cost is due to the fact that the removal must occur with minimal damage below, officials explained. The company will use large cranes and special equipment, and the work is considered especially dangerous.
The albizia trees are scheduled to be removed two per month between now and February. Once they are removed, the arboretum will grow new plants that will be screened for their weed risk to avoid invasive species like the albizia, officials said.
Other albizia trees within the arboretum have been identified for future removal once funding becomes available, they said.
Evensen said the trees will be chipped and mulched on-site, and the logs will be disposed at the arboretum to recycle nutrients and minimize traffic and inconvenience to Manoa residents. Keeping the disposal on-site will save several hundred thousand dollars in hauling costs, he said.
More than 5,000 different tropical and subtropical plants can be found at the 193.5-acre arboretum situated at the top of Manoa Valley. The arboretum will remain open during the project, but access to tree removal zones will be restricted for safety reasons, officials said.
