By JC Watson and Frankie Koethe with Dale Moana Gilmartin
Concerned about flooding in Mānoa and other nearby streams? Look no further than invasive trees causing massive debris pile-ups leading to streams overflowing their banks, destroying property, and endangering lives. A prime culprit in these floods is the dreaded Albizia (Falcataria moluccana).
Native to Papua New Guinea, Indonesia and the Solomon Islands, Albizia is a tropical tree introduced to Hawaiʻi in 1917 by Joseph Rock for ornamental and reforestation purposes. Roughly 140,000 Albizia were planted in forestry areas throughout the state during what are now considered misguided efforts in forestry planting during the early 20th century.
Albizia truly is one of the fastest growing trees on Earth. Growing up to 15 feet per year and easily reaching heights of over 100 feet, these trees produce a massive number of structurally brittle trunks and limbs. Live branches can suddenly plummet to the ground with no sign of physical weakness or apparent cause. A mature Albizia is a dangerous, brittle, breakage-prone structure posing a serious threat to watersheds, roads, structures, power lines, and human health.
The Hawaiʻi-Pacific Weed Risk Assessment scores Albizia as highly invasive. Albizia can thrive in a variety of soil conditions and can become established in intact native ecosystems. The tree’s massive quantities of seeds are encased in light, papery pods and are easily dispersed by the wind.
Fortunately, with early action, Albizia can be controlled. Chemical and non-chemical control methods, including hand-pulling, ring-barking and incision point application with low-doses of herbicide, are used to control both seedlings and mature trees.
The fastest and easiest way to combat Albizia infestation is to control the seedlings, but time is of the essence! There is a mere one-year window when seedlings can be manually pulled up and removed. After that, trees will need to be cut down or treated in place. Any Albizia tree over 15 feet tall must be assessed to see if it poses a hazard to infrastructure or property. Trees posing a hazard to structures, roads and streams should never be treated and left standing. It is strongly recommended that a certified arborist be consulted regarding removal of large Albizia trees.
Large-scale infestations across the state may indicate that control of the Albizia population is near-impossible, but a dedicated group of organizations and individuals have not shied away from taking on the fastest growing tree in the world. In 2018, the Hawaiʻi Invasive Species Council developed a strategic plan to address Albizia infestations statewide with a holistic plan to combat this notorious invasive species across the state.
On Oʻahu and Hawaiʻi Island, programs have been created by the Koʻolau Mountains Watershed Partnership (KMWP) and Big Island Invasive Species Committee (BIISC) to combat Albizia across the landscape by working hand-in-hand within communities.
Through education and empowerment initiatives, KMWP and BIISC are spreading the word to interested neighborhoods and stakeholders. Aptly named community control teams, such as the Rapid Albizia Death Hui (RAD) on Oʻahu and Albizia Assassins on Hawaiʻi Island, coordinate and train volunteers to identify, treat, and track removal efforts to reduce Albizia populations.
For more information on Albizia control, visit the Koʻolau Mountains Watershed Partnership web page at: http://koolauwatershed.org/albizia.
Portions of this article were previously published in Hawaiʻi Landscape magazine.