Welcome to Earth Week on Nightingale, the journal of the Data Visualization Society. In honor of Earth Day on April 22, we are publishing earth-related data-visualization content all week. Data viz can enhance our appreciation of the planet, illuminate our relationship to it, and call us to action to preserve it. After all, we only have one and it means the world to us. You can keep up with all of our Earth Week articles here.
The Mighty Seed
The seed of the most important tree in Hawai‘i’s native forests is no bigger than an eyelash and yet manages to wedge itself in the cracks of freshly hardened lava rock, take root, grow 100 feet tall, and live for upwards of 1,000 years. An estimated 350 million ‘ōhi‘a (five different species, primarily Metrosideros polymorpha) grow across more than 800,000 acres in Hawai‘i, critical to the archipelago’s complex web of endangered flora and fauna.
As the most prevalent tree in the forest, ‘ōhi‘a embedded itself into Hawai‘i’s culture, both practically and spiritually, in traditional as well as modern times. Its wood is used for carving statuary and building structures, and its flowers and leaves woven into lei. ‘Ōhi‘a is celebrated in chants, song, and dance. What’s more, ‘ōhi‘a’s physiology — from its pubescent “hairy” leaves to spiky stamen — captures rainwater and protects watersheds to provide water for drinking and for all life. For the people of Hawai‘i, ‘ōhi‘a is revered and celebrated. In fact, tomorrow, Saturday, April 25, is the annual ‘Ōhi‘a Lehua Day, which has quickly pivoted to a, mostly, online celebration.
Unfortunately, about 10 years ago, ‘ōhi‘a seemed to start dying overnight, as the ovate-shaped leaves on the trees’ entire crowns dried up and turned reddish-brown, alarming cultural practitioners and scientists alike. In 2014, the killing culprit was identified as a previously unknown microscopic fungus. Eventually, two different species of fungi were named, with the more aggressive of the two called Ceratocystis lukuohia. Or “destroyer of ‘ōhi‘a.”
The fungus grows in a layer of wood beneath the bark, clogging the flow of water, causing it to die. For a tree that can live hundreds of years, dying in a few weeks is pretty rapid; hence, the disease name, Rapid ‘Ōhi‘a Death. Early on, it was thought that burrowing beetles played a role in the spread of the disease, and subsequent science has proved that. As beetles burrow into the wood where the fungus colonizes, frass, a sawdust-like substance, excreted by beetles, can contain live fungal spores. This material easily blows in the wind and moves around the island in mud by humans and animals. For another tree to be infected, it must have a fresh wound — say, a broken branch during windy weather, braised bark by feral animals, or pruning by humans.
On Hawai‘i Island, where the fungi were first detected, over one million ‘ōhi‘a have died. More recently, the disease was confirmed in more than 100 trees across Kaua‘i, in a scattering on O‘ahu, and one tree on Maui.
A Monumental Effort
As the news of Rapid ‘Ōhi‘a Death emerged, scientists got busy. One group started testing to determine whether one species or one variety of ‘ōhi‘a were, possibly, more resistant to the fungi. Another group, the Hawai‘i Seed Bank Partnership, quickly ignited a statewide effort to collect and bank seeds from the many different seed zones across the archipelago. A seed zone is a geographic area within which plant materials can be transferred with little risk of being poorly adapted to their new location. That way, if need be, reforestation efforts could include ‘ōhi‘a best adapted for the specific environment.
Hawai‘i is known for its variety of microclimates, from arid to very wet. Over millennia, ‘ōhi‘a seeds blew to all parts of the islands, adapting and often hybridizing to result in the five different species and 11 different varieties found today that are all endemic to Hawai‘i. That is, found in Hawai‘i and nowhere else in the world. But not all species and varieties are located on every island. Some are island endemics. Others are ecosystem specific like one variety of Metrosideros polymorpha known as pumila, that only grows in bogs.
The goal of collecting seeds from 500 to 1,000 trees of each species and variety was established. That translates to hundreds of millions of seeds.
Sounds daunting but the unexpected boost to this effort is coming from the people of Hawai‘i, who have embraced the spirit of Earth Day in their everyday lives. Viewing ‘ōhi‘a as a respected elder, they are lacing up their boots and joining botanists to collect ‘ōhi‘a seeds. The response of both the community and scientists is telling. Hawai‘i is home to numerous rare and endangered species. ‘Ōhi‘a isn’t one — yet. In fact, ‘ōhi‘a is the most common tree in Hawai‘i’s native forest, and that’s the reason its loss would be devastating. Here, people know ‘ōhi‘a is more than just another tree. It’s the tree of life.
Special thanks to Kim Steutermann Rogers who contributed writing and research to this project, and to my husband, Vincent Wang, who helped me untangle the complex data.