Albizia in Hawai‛i

Falcataria moluccana was introduced to Hawai‛i from the Moluccan Islands in Indonesia over 100 years ago. Territorial foresters at that time were concerned about slopes that were eroding due to land uses like cattle ranching and logging, and they wanted to plant very fast-growing trees. When the sugar cane industry collapsed, albizia invaded abandoned cane fields and spread even further throughout the islands.

Albizia may be the fastest-growing tree in the world – but only in Hawai’i. Without the co-evolved pests that slow down its growth in its native range, Falcataria moluccana displays astonishing growth rates. Like other members of the family Fabaceae, albizia has the ability to fix nitrogen from the air which enables its rapid growth. A young albizia tree can grow as much as 20′ in its first year – a rate of more than a foot every two weeks! Trees continue to grow 10′ per year to over 200 feet tall.

Trees mature and are able to produce seeds by 4 years of age. The seeds are wind-dispersed, allowing them to spread quickly over large areas. For instance, in the Rainbow Falls area of Hilo, the albizia population grew from 10 acres to 35 acres in 15 years – a 253% increase.

Albizia has long been identified as a serious threat to native forests. The large, broad canopy of albizia shades out the understory, a death sentence for our native trees like ‛ōhia or ‛āma‛u. The nitrogen added by albizia makes the soil more welcome to aggressive invasive understory weeds that are shade-tolerant and can survive in the albizia understory. These invaders take up all remaining resources, preventing keiki plants of many native species from developing.

Albizia is estimated to have invaded over 5000 acres in the Puna district alone, and small but spreading populations can be seen all over the island, including Kohala and Kā‛ū. Currently, albizia can commonly be found below 3000′ elevation in areas with moderate to heavy rainfall: areas that feed our freshwater system. On islands like O‛ahu and Kaua‛i, albizia can be found right at the summit of steep mountain watersheds, the source of those islands’ fresh water.

Because the trees grow so fast, the wood that develops is brittle and weak. Albizia is prone to sudden limb drop where limbs will break off and fall with no apparent disturbance. The wood is also prone to rot and insect infestation, so there may be hidden weaknesses. Very large branches have been recorded breaking and falling in heavy rain or with wind gusts.

Albizia is a life-threatening tree. In 2009 and again in 2014, motorists in Puna narrowly escaped being crushed when falling albizia limbs fell on their cars. During Tropical Storm Iselle in 2014, dozens of people were trapped for hours, and many homes were severely damaged by toppled albizia. In 2016 a worker was killed in Kauai by a falling albizia branch.

Albizia also poses a huge economic cost for residents of Hawaii. In addition to the cost of removing trees that are direct threats, Hawaiian Electric, HDOT, and County DPW routinely deal with the impacts of trees falling from private property onto roads and power lines. Tropical Storm Iselle left 30,000 people without power, some for weeks, due to downed power lines and poles. Three smaller storms in the months following Iselle caused power outages for 5,000 or more customers for up to 4 days each.

By 2017, the Hawai‛i Island branch of the state DOT estimated that 90% of all calls about fallen trees were for albizia. HDOT reported that a single day of response to a small storm event in early 2015 cost over $12,000 in overtime, equipment, and materials. In addition to causing budget overruns and staff shortages in the short term, frequent overtime charges have a long-term effect on state budgets. These costs directly impact consumers and taxpayers.

In agricultural settings, using wood chips from untreated albizia has the potential to bring some desired N into the soil. However, this is not guaranteed across all crops. Research from UH Hilo, supported by BIISC, showed some crops benefitting from albizia input at a rate equal to that of commercial fertilizer. It is recommended that farmers test albizia mulch against other fertilizers on each potential crop to ensure desired results are attained.

In natural settings, N from the prolific amounts of leaf litter and dropped branches of albizia are harmful to native ecosystems. The relatively young volcanic soils of Hawai‛i are known to be nitrogen-poor, and the native plants of Hawai‛i are specially adapted to grow in such soils – one of the few advantages they have over introduced plant species. When albizia is present, the added nitrogen improves conditions for species like Koster’s curse, strawberry guava, and other invaders that can use that free fertilizer to displace native plants.

At first, yes, but over time the tree’s rapid growth will slow, and the carbon balance becomes static. Keep in mind that as albizia spreads, it will shade out and prevent the growth and regeneration of most other plants growing under its canopy, losing the potential for carbon captured through that flora. Many other native and non-invasive trees can be used to capture carbon without the threat to human health and our native ecosystems.

Carbon in existing trees is not lost through control. When a large tree is cut, chipped, and returned to the soil, the carbon remains captured and improves soil for farmers and gardeners. New useful plants can grow, and begin capturing carbon, instead. Similarly, if the tree is treated in place with a small dose of herbicide, the carbon–and the herbicide–remain locked up in the wood. The tree slowly falls apart, returning the carbon to the soil. The herbicide degrades during this time period into harmless carbohydrates.

First, never bulldoze a lot until just before you are ready to use it. Open, disturbed spaces are prime real estate for albizia and other invasives to move in.

If you are not looking to bulldoze right away, are clearing by hand, or only have small pockets of trees to address, start by determining whether any of the trees are hazardous. A hazard tree is not necessarily defined by size, but by the potential impact of falling limbs or a toppling trunk. The determining factor in deciding how an individual tree should be dispatched lies in its proximity to structures that could pose a threat. Eventually, the branches of dead trees will fall, so you need to be sure that the tree you are treating does not pose a threat to structures, roads, or power lines.

For non-hazardous trees, BIISC recommends using very small amounts of Milestone herbicide applied to small cuts into the vascular tissue of the tree. Known as the incision point method or hack-and-squirt approach, this method cause trees to lose their leaves over the course of a couple of weeks, and is an easy and inexpensive way to treat young albizia. This method may be used on very large trees, but keep in mind that the area will not be safe until the heavy limbs have completely fallen from the tree. This can take 3-5 years. (BIISC offers hands-on training in albizia control – follow us on Facebook or Instagram for notifications of these opportunities!)

Large or hazard trees that pose a potential threat to structures should be risk-assessed and removed by a certified arborist. A list of arborists who remove albizia can be found here. Any stumps should be treated with herbicide, as albizia will readily regrow from a cut stump and form an even more difficult multi-stump mess.

A qualified arborist must be certified for the required work, carry a class C27b contractor’s license (for work over $1,000), and carry insurance. There are separate certifications for tree care workers (under the supervision of a certified arborist), arborists, risk assessors, and working near power lines. An arborist is not required to be bonded, but if your tree threatens significant property or public access areas, you may want to explore this higher level of financial backing. Keep in mind that albizia does not behave like other trees, and you should not have your cousin from the mainland come in to help. Your arborist should have experience felling albizia in Hawai‛i and be able to provide local references.

A list of arborists who remove albizia can be found here.

Property owners with hazard trees face significant costs in tree removal, but the potential cost of damage to your neighbor’s property is likely to be much, much steeper. In HPP, one resident repeatedly requested the removal of a hazardous albizia on a neighboring property. The arborist estimate of $6,000 was far less than the $250,000 damage claim that resulted when the tree blew over during Tropical Storm Iselle and crushed the neighbor’s house.

There may be some assistance available in obtaining funding for the removal of hazard trees. The USDA Rural Development section offers low-cost loans and grants for property owners that in limited circumstances may be used to pay for the removal of hazard albizia trees. Please contact the USDA Rural Development office in Hilo for more information on requirements for eligibility.

Hazardous albizia is often not directly caused by the current homeowner, but a legacy left by land mismanagement over decades. Reach out to your local and state representatives to let them know that you support legislation to provide relief for homeowners who need financial support to hire arborists to remove hazardous albizia.

First, you should contact a certified arborist to do a hazard assessment to ensure that none of the trees pose imminent danger. (If any trees are assessed as a hazard, follow the directions in the section below about hazardous albizia on neighboring properties).

If the trees are assessed as non-hazardous, the next step is to alert the property owner of the developing threat (we have provided a sample letter template you can use). Make copies of all documents, send the letter by certified mail, and save the return receipt proving that the notice was sent and received by your neighbor.

HI Rev Stat § 708-804 (2020) protects residents from a trespass charge if they enter a neighboring property for the purpose of controlling albizia (either through treating w/ herbicide or hiring an arborist to fell the tree). This statute requires two notifications to the property owner, so be sure to follow the requirements carefully!

The first step is to contact the owners and let them know of their albizia problem, especially if the trees pose a potential threat to structures on neighboring properties. Include photos of the tree and structure(s) it threatens. The best approach is to make copies of all documents, send the letter by certified mail, and save the return receipt proving that the notice was sent and received by your neighbor.

You can find step-by-step support on contacting property owners and preparing documentation to file complaints here.

Once you have contacted the property owner with information about the specific trees and hazard of concern, and have provided them with the relevant state and county laws related to hazard trees, you should wait 30 days for a response. After that, you can take your complaint to the Hawai‛i County hazard mitigation program.

Hawaii County:
Chapter 14 (Sec 14-150, ordinance 20-86) of the Hawai‛i County Code addresses trees within the front 100 feet of the property facing a county road, or that pose an imminent danger to a neighboring property. Mention in your complaint the precise location of the property and tree (the county map link is a big help), the letter you sent your neighbor, the certified mail receipt, and a brief description of the hazardous situation (take photos and keep them handy). Keep all these materials together. When using this form to report hazardous albizia trees, select the option Unsafe flora posing imminent danger. Complaints can be submitted to the Hawai‛i County Department of Public Works here.

No, these laws do not absolve homeowners of the responsibility to maintain their own property. If you believe a situation exists on your property that could become a hazard to others, contact a reputable arborist to assess the situation for you, and review your insurance coverage. If the state or county acts to mitigate the hazard on a property, the law allows the agency to bill the property owner for the cost of mitigation and a lien may be placed against the property. Most homeowners find that it is cheaper to deal directly with contractors rather than reimbursing government agencies after the fact.

As a project of the University of Hawai‛i, we pursue grants to support albizia mitigation for Hawaii County while lobbying for additional legislative solutions. BIISC has worked with multiple agencies and subdivisions to control albizia in high-priority areas using a combination of chemical treatment and arborist removal. The lower portion of the Puainako Extension and Maku’u Drive from Railroad to the highway are some examples of critical corridors identified in the albizia mitigation plan that have been controlled through collaborative efforts led by BIISC. You can learn more about BIISC’s work on albizia by watching our recorded webinar.

Additionally, BIISC supports individuals and communities directly with education and training as part of our Albizia Assassins program. Contact us for more information.

It is important that you let your County, State, and Federal elected know that albizia is a key area of concern for you. BIISC provides updates and notifications for providing testimony on pending legislation regarding albizia on our Facebook page. Like us to receive information about upcoming legislative hearings for albizia and other invasive species issues.