Categorized | Featured, Sci-Tech, Volcano

Volcano Watch: Lava-loving ‘ōhi‘a lehua is a pioneer plant in peril

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

A young ‘ōhi‘a tree with its red lehua blossoms grows near a steam vent on the solidified crust of the 1959 Kīlauea Iki lava lake in Hawai‘i Volcanoes National Park. ‘Ōhi‘a trees thrive on volcanic landscapes ranging from sea level to 2440 m (8,000 ft) elevation and are among the first plants to grow on new lava flows. Photo courtesy of Nate Yuen (hawaiianforest.com).

A young ‘ōhi‘a tree with its red lehua blossoms grows near a steam vent on the solidified crust of the 1959 Kīlauea Iki lava lake in Hawai‘i Volcanoes National Park. ‘Ōhi‘a trees thrive on volcanic landscapes ranging from sea level to 2440 m (8,000 ft) elevation and are among the first plants to grow on new lava flows. Photo courtesy of Nate Yuen (hawaiianforest.com).

One of the wondrous things about visiting a young lava flow on the Island of Hawai‘i is encountering the tenacious plant life that emerges from a barren and rough volcanic environment. Volcanophile hikers know that taking a tumble on the sharp, glassy lava surface can leave a lasting impression. Yet, within a few years, a recent lava flow can host a community of plants that includes ‘ōhi‘a lehua (Metrosideros polymorpha)—one of the most common trees in Hawaii and the first native tree to colonize young lava.

From its humble beginnings on a barren flow, ‘ōhi‘a lehua, or ‘ōhi‘a, becomes the dominant tree of the Hawaiian rain forest. This keystone species, which holds the entire forest ecosystem together, evolved in complete isolation, and occurs nowhere else in the world. The tree’s original relatives are likely from New Zealand, with the wind-borne seeds making their way to Hawaii by way of the Marquesas Islands.

The ‘ōhi‘a tree is adapted to colonize lava flows in an unpredictable volcanic environment. Mature ‘ōhi‘a forests always have some flowering trees, so the tiny, light-weight seeds are available year round to be dispersed to recent flows. The tree has a superior capacity for extending its roots vertically and can grow efficiently in cracks and fissures, taking advantage of residual moisture after rainfall. ‘Ōhi‘a also have the capability to close their stomata, or breathing pores, so the trees can “hold their breath” when toxic volcanic gases are blown their way.

‘Ōhi‘a is a tree with immense cultural significance, symbolizing strength, beauty, and sanctity. It is considered the physical manifestation of Kū, one of the four principal Hawaiian deities. The wood was used in sacred structures for heiau (temples) and for weapons and tools. The red, orange, and yellow lehua blossoms are a symbol of Pele, the goddess of fire and volcanoes. The ‘ōhi‘a is entwined with the art of hula, with its flowers and foliage frequently adorning the dancers and presented as offerings by traditional halau (hula schools).

‘Ōhi‘a Lehua blossoms at Kilauea Caldera with Halemaumau Overlook Vent in the distance. Photography by Baron Sekiya | Hawaii 24/7

‘Ōhi‘a Lehua blossoms at Kilauea Caldera with Halemaumau Overlook Vent in the distance. Hawaii 24/7 File Photo

Unfortunately, there is a new menace threatening this important tree: a fungus, Ceratocystis fimbriata, that is causing a lethal disease in ‘ōhi‘a. Known as ‘ōhi‘a wilt, or Rapid ‘Ōhi‘a Death (ROD), a diseased tree exhibits rapid browning of the leaves on a single limb and/or in the entire tree crown and typically dies within a matter of weeks. Researchers report that nearly all of the trees in an affected stand will succumb to the disease within two to three years. This has the potential to change the evolution of the volcanic landscape and forest ecosystems in Hawaii, putting our unique Hawaiian birds, invertebrates, plant communities, and, potentially, entire watersheds at risk.

Currently the disease is confined to the Island of Hawai‘i. However, it is spreading from the island’s lower Puna and Hilo Districts (East Hawai‘i), where it was originally identified, to West Hawai‘i and Volcano, and has the potential to kill ‘ōhi‘a trees statewide.

Since there is no treatment or cure for the disease at this time, the main tactic for managing ROD is to prevent the disease from spreading. In August, the Hawaii Board of Agriculture imposed a quarantine on the intrastate movement of ‘ōhi‘a wood and plant parts without a special permit (hdoa.hawaii.gov/blog/main/ohia…). When visiting or working in Hawai‘i Island forests, you should treat shoes, gear, tools, vehicles and clothing with a fresh 10 percent bleach solution, or greater than 70 percent rubbing alcohol, before moving to another forested area (www2.ctahr.hawaii.edu/forestry…). Most importantly, ‘ōhi‘a wood, vegetation, or soil, should not be moved from its original location.

This winter and holiday season is different than previous ones because of ROD. Residents who use wood to heat their homes should consider that buying ‘ōhi‘a fire wood may spread ROD to trees in their areas. This year, wreath-making workshops include topics on preventing the spread of ROD, and wreath and lei makers are being encouraged to explore foliage alternatives to ‘ōhi‘a.

Next time you pass by an ‘ōhi‘a, take a moment to appreciate the pioneer tree that shapes the volcanic landscape in Hawaii. More information and details on preventing the spread of Rapid ‘Ōhi‘a Death is available on the College of Tropical Agriculture and Human Resources website (www.rapidohiadeath.org) and on Facebook (www.facebook.com/RapidOhiaDeat…)

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