Partnerships in Hawai’i Making Progress Against an Invasive, Dangerous Beauty

Albizia Tree rises above the forest in this aerial photograph.

Courtesy photo by Big Island Invasive Species Committee (BIISC)

To the untrained eye, the albizia framing Hawaiian highways and horizons are an attractive sight. Although they have appealing aesthetics – tiny leaflets, pink pom-pom flowers, and umbrella-shaped crowns – these trees are an invasive, dangerous beauty on these Islands.

Alibiza (Falcataria moluccana) are abundant in Hawai’i, but they are not native. After botanist Joseph Rock brought albizia to the Islands as ornamentation and for reforestation, the species spread easily to new areas due to its plentiful production of wind-borne seeds and ability to thrive in nutrient-poor soils. In the absence of the natural predators found in its native range – Indonesia, Papua New Guinea, and the Solomon Islands – albizia has proliferated in Hawai’i.

We might be tempted to see this as a cause for celebration. Don’t we want more trees? As the story of albizia in Hawai’i illustrates, trees are good things only if they are the right species in the right place, especially where native ecosystems are threatened.

Danger to Forest Health

Once established, this aesthetic assailant moves in quickly in disturbed areas, such as hurricane blowdown, and outcompetes native vegetation. This is especially concerning for Hawai’i’s many native plants – including the iconic ohi’a – that are found nowhere else in the world. Albizia increase nitrogen levels in soil, which negatively impacts native plants that evolved in Hawaiian volcanic, naturally nutrient deficient, soils, while allowing other invasive plants to bloom. With decreased availability of native plants, native wildlife is deprived of the food and habitat they need for survival.

Albizia Tree rises above the forest in this aerial photograph.

Courtesy photo by J.B. Friday

Threat to Public Safety

In addition to catalyzing a chain of harmful effects on forest health, the shallow roots and breakable structure of albizia are public safety hazards. As members of the legume family, albizia can be thought of as giant woody beans. They grow fast and tall, adding 15 feet per year and reaching upwards of 100 feet tall at maturity. This rapid growth rate is why these trees have weak and brittle wood and are prone to “sudden large branch breakage,” which endangers homes, infrastructure, and human life.

“Although we had been supporting efforts to address the albizia problem for years, Tropical Storm Iselle put a spotlight on the urgency of the issue in 2014,” said Jodi Chew, Pacific Island Liaison, Pacific Southwest Region. “During the storm and its aftermath, albizia became public enemy number one in Hawai’i.”

The destruction caused by albizia was staggering. Broken branches and downed trees blocked roads and damaged power lines, leaving hundreds of Hawaiian residents stranded without power for days. Fallen albizia and associated debris also clog, destabilize, and divert waterways, which increase the risk of flooding.

“Hazard trees are a big problem for us and there are more albizia on the Islands than we can deal with alone,” said Rob Hauff, Protection Forester with the Hawai’i Department of Land and Natural Resources, Division of Forestry and Wildlife (DOFAW). “That is why community-based initiatives and working with partners is so important.”

Partnerships to the Rescue

In Hawai’i, restoring and protecting forest health is all about partnerships. Although this can be seen throughout the continental United States, the U.S. Forest Service (USFS) is deeply integrated with partners on the Islands, celebrating the fact that it is more rewarding to work together. Collaborations between the USFS and partners like DOFAW have grown through cultivating a strength of trust and regularly exchanging perspectives on the world. As the success stories surrounding albizia demonstrate, partners coming together in shared stewardship are blazing pathways to restore and sustain forest health.

Research

For over 15 years, USFS researchers have worked with research partners to understand the best methods of beating back albizia. For example, collaborative studies have confirmed that Incision Point Application (IPA) is an efficient, inexpensive control method for trees growing at a safe distance (100 meters) from infrastructure. Through this method, a small, lethal dose of herbicide is injected directly into the vascular system of albizia, keeping the surrounding environment unimpacted by the herbicide’s effects. In stark contrast to the hazardous, sudden breaks of untreated trees during a wind event, IPA causes albizia to deteriorate gradually: leaves drop after a few weeks, fine branches fall within a few months, and the trunk decomposes after a few years. Through this highly effective treatment, full sunlight reaches the understory, accelerating a resurgence of native plants.

An Albizia tree is in the process of being removed by a forester wearing a hard hat

Courtesy photo by Big Island Invasive Species Committee (BIISC)

“Through years of ongoing, collaborative research, we have been able to recommend IPA and a post-treatment protocol to empower community partners to combat this invasive in their neighborhoods,” said Flint Hughes, USFS Research Ecologist at the Institute for Pacific Island Forestry.

Community Engagement

There are a variety of community-driven efforts that are helping to control the spread of this damaging intruder, many of which are applying research findings on the ground. For example, the USFS has funded and supported the Big Island Invasive Species Council’s “Albizia Assassin” Program, which provides community events and trainings to help local residents learn how to uproot seedlings and apply IPA on smaller trees. Additionally, the Koolau Watershed Partnership – a recipient of a USFS Forest Health Grant – has created multi-media resources to help residents become aware of the hazards, learn how to identify albizia, and understand the best methods of removal.

Wood Innovation

The USFS is also a partner of the Albizia Project, which is developing innovative uses for this invasive tree and supporting native ecosystem restoration. Although albizia do not naturally have ideal structural wood, this project developed an engineered wood system of glue-laminated panels that improves its strength and stability. The demonstration structure built with laminated albizia wood could become a prototype for prefabricated Accessory Dwelling Units (ADUs) – small, independent residential units. If the state’s building code is changed to permit laminated albizia wood, these ADUs could accomplish a few things at once: help to remove an invasive species, stimulate the local industry, create jobs, and assist with a housing crisis.

“Prevention, removal where needed and possible, and community engagement are paramount, but wood product innovation is a way of making the best of a bad thing,” said Larry Swan, Wood & Biomass Utilization Program Leader, Pacific Southwest Region. “We are committed to doing everything we can to limit the spread of albizia, while also collaborating with partners to use to the wood where we are able.”

An Albizia tree is in the process of being removed by a forester wearing a hard hat

Forest Service Photo by Larry Swan

Much like wildfire, invasive species like albizia do not recognize jurisdictional boundaries. Applying a multi-pronged approach through partnerships across all lands is transforming the challenges of this dangerous beauty into an anthology of restoration success stories.

To learn more about albizia, please visit:

Hawaii Invasive Species Council 

Koolau Watershed

Big Island Invasive Species Committee

Albizia Project