Mycelium Connections - Biodiversity for a Livable Climate

What tree has adapted to grow directly in lava rock and is a keystone species of the Hawaiian watershed?

‘Ōhi’a Lehua (Metrosideros polymorpha)!

Image Credit: Kevin Faccenda via iNaturalist

The first time I saw the vibrant blossoms of the ‘ōhi’a lehua tree, I was walking on a dirt path in Kauai’s Waimea Canyon State Park, gaping down at the most colorful red and green gorges I had ever seen. Needing a breather from the steep visual plunge, I looked up from the canyon and noticed bright red flowers on the side of the path. As I got closer and could see the plant more clearly, the first thought that popped into my head was how similar the flowers looked to those fiber optic light toys I had played with as a kid. (If you don’t know what fiber optic light toys look like, look them up. You’ll see exactly what I mean.)

After my trip to Waimea Canyon, I saw ‘ōhi’a lehua everywhere. When I drove along the coast between the beach and the sloping mountains, when I hiked the volcanic craters of Haleakala, and when I visited parks and gardens across the islands that protect native plants and animals. ‘Ōhi’a lehua is the most common native tree in Hawaii, so seeing its fiery red, orange, or yellow blossoms every day felt so very ordinary. But ‘ōhi’a lehua is far from ordinary.

Image Credit: Ed Sharron via iNaturalist

Let Me Introduce You to My New Friend, ‘Ōhia Lehua

Endemic to the six largest islands of Hawaii, ‘ōhi’a lehua is the dominant tree species in native forests, present in approximately 80% of the total area of these ecosystems and covering close to one million acres of land across the state. Depending on where exactly it grows, its size can vary widely, from a small shrub to a large tree. Found only in the Hawaiian archipelago, ‘ōhi’a lehua grows at elevations from sea level to higher than 9000 feet, and in a variety of habitats like shrublands, mesic forests (forests that receive a moderate amount of moisture throughout the year), and more wet, or hydric, forests.

You can easily identify the ‘ōhi’a lehua blossoms by their mass of stamens – the part of the flower that produces pollen – which are slender stalks with pollen-bearing anthers on the end. It’s what made me think the ‘ōhi’a lehua looked exactly like those fiber optic light toys. These powder puff-like flowers are most often brilliant shades of red and orange, but yellow, pink, and sometimes even white ones can be found.

‘Ōhi’a lehua grows slowly, reaching up to 20-25 meters (66-82 feet) in certain conditions.

With a little help from the wind, the seeds of ‘ōhi’a lehua travel from the tree and settle in cracks in the ground of young lava rock. It is, in every sense, a true pioneer plant. As one of the earliest plants to colonize and grow in fresh lava fields, ‘ōhi’a lehua stabilizes the soil and makes it more habitable for other species.

Even though ‘ōhi’a lehua can blanket Hawaii’s native forests, this flowering tree also grows alone, as you can see in the photograph below. Plants like ‘ōhi’a lehua fill me with happiness because they are able to grow in the most harsh, barren, and disrupted places, and they make it possible for other species to do the same. Plants like ‘ōhi’a lehua fill me with surety that even though sometimes poorly treated, the natural world will continue to be strong. Plants like ‘ōhi’a lehua make me believe in the resilience of nature.

Arid, rocky, Mediterranean coast. (Via Pexels)

How ‘Ōhi’a Lehua Cares for the Hawaiian People

Biodiversity forms the web of life we depend on for so many things – food, water, medicine, a stable climate, and more. But this connection between human beings and natural life is not always clear, understood, or appreciated. But there is a concept in Hawaiian culture called aloha ‘āina, or love of the land, which teaches that if you take care of the land, it will take care of you. The ‘ōhi’a lehua in particular takes care of the Hawaiian people in a pretty special way.

One of the most important characteristics of this flowering evergreen tree is that it’s a keystone species, protecting the Hawaiian watershed and conserving a great amount of water. The way I see it, ‘Ōhi’a lehua is an essential glue that holds Hawaii’s native ecosystems together. The leaves of ‘ōhi’a lehua are excellent at catching fog, mist, and rain, replenishing the islands’ aquifers and providing drinking and irrigation water for Hawaiian communities. ‘Ōhi’a lehua’s ability to retain water, particularly after storms, not only makes that water accessible for other plants, but it helps mitigate erosion and flooding. The tree provides food and shelter for native insects, rare native tree snails (kāhuli), and native and endangered birds like the Hawaiian honeycreepers (‘i’iwi, ‘apapane, and ‘ākepa). ‘Ōhi’a lehua trunks protect native seedlings and act as nurse logs, providing new plants with nutrients and a growing environment.

‘I’iwi, the Scarlet Hawaiian Honeycreeper, perched on an ‘ohi’a tree (Image Credit: Nick Volpe)

The Myth of ‘Ōhi’a Lehua

‘Ōhi’a lehua may have a disproportionately large effect on Hawaii’s ecosystems as a keystone species, but its presence as a meaningful part of Hawaiian culture could be even larger. There are many versions of mo’olelo (story) about the origin of the ‘ōhi’a lehua tree, but the most common one is about young lovers named Ōhi’a and Lehua. Pele, the goddess of the volcano, changed herself into a human woman and tried to entice ‘Ōhi’a. When he denied her, Pele became enraged and transformed ‘Ōhi’a into a tree. When Lehua found out, she was so heartbroken that she prayed to the gods to somehow help her reunite with him. Answering her prayers, the gods transformed Lehua into a flower and placed her on the ‘ōhi’a tree’s limbs. To this day, it’s believed that whenever a lehua flower is picked, the skies will open up and rain will fall, because the lovers have been separated.

‘Ōhi’a Lehua as a Cultural Symbol

In Hawaiian culture, the ‘ōhi’a lehua is a symbol of love, resilience, and ecological harmony. The transformation of Ohia and Lehua into tree and flower represents the inseparable bond between two people who love each other, and between the tree and its flowers. The term pua lehua, or lehua flowers, is often used to describe people who express the same grace, strength, and resilience of the ‘ōhi’a lehua. Pilina, a Hawaiian word that means “connection” or “relationship,” is an important value in Hawaiian culture because it is a critical way for people to connect with and understand the world around them. The ‘ōhi’a lehua tree is a symbol of pilina, and embodies this relationship between the Hawaiian landscape and its people.

Hula dancers performing at the Merrie Monarch Festival
Thomas Tunsch (**CC BY-SA** )

The ‘ōhi’a lehua is also incredibly important to hula. Hula is the narrative dance of the Hawaiian Islands, and it is an embodiment of one’s surroundings. Dancers use fluid and graceful movements to manifest what they see around them and tell stories about the plants, animals, elements, and stars. ‘Ōhi’a lehua trees and forests are considered sacred to both Pele, the goddess of the volcano as you may recall, and Laka, goddess of hula. To enhance their storytelling and evoke the gods, dancers traditionally wear lehua blossoms or buds in lei, headbands, and around their wrists and ankles.

The Dependability of ‘Ōhi’a Lehua

‘Ōhi’a lehua has long been a part of daily life. Historically, the hardwood of the tree was used for kapa (cloth) beaters, papa ku’i ‘ai (poi pounding boards), dancing sticks and ki’i (statues), weapons, canoes, and in the construction of houses and temples. Today, the tree’s wood is used for flooring, furniture, fencing, decoration, carving, and firewood. ‘Ōhi’a lehua blossoms decorate altars for cultural ceremonies and practices. Flowers, buds, seeds, and leaves form the base of medicinal teas that can stimulate appetite and treat childbirth pain.

Threats to ‘Ōhi’a Lehua

As a native tree, ‘ōhi’a lehua competes with invasive species for moisture, nutrients, light, and space. Plants like the strawberry guava plant (Psidium cattleyanum) grow in dense thickets and block the growth of ‘ōhi’a seedlings. The invasive fountain grass (Pennisetum setaceum) can dominate barren lava flows, making it difficult for ‘ōhi’a to compete. ‘Ōhi’a lehua is also threatened by non-native animals. Hooved animals like pigs, cattle, goats, and deer disturb the soil, eat sensitive native plants, and trample the roots of ‘ōhi’a lehua trees.

The most dangerous threat to ‘ōhi’a lehua is a virulent fungus called Ceratocystis fimbriate, which attacks the tree’s sapwood, preventing it from uptaking water and nutrients, and killing the tree within weeks. It’s been given the name Rapid Ohia Death (ROD) because of how quickly it suffocates the tree, turning the leaves yellow and brown and the sapwood black with fungus. Infections spread through a wound in the bark, which can be caused by animals trampling roots, lawn mowing, or even pruning, and can be present in the tree for up to a year before showing symptoms. ROD is spread by an invasive species of wood boring Ambrosia beetle that infests the tree and feeds off the fungus. When colonizing trees, the beetle produces a sawdust-like substance made of excrement and wood particles called frass, which can contain living fungal spores that get carried in wind currents and spread by sticking to animals and human clothes, tools, and vehicles.

Since its discovery in 2014, ROD has killed more than one million ‘ōhi’a lehua trees across 270,000 acres of land, making it a significant threat to biodiversity and cultural heritage. The International Union for Conservation of Nature (IUCN) classifies ‘ōhi’a lehua’s conservation status as vulnerable, and has recorded a decline in mature trees since 2020. Because ROD can spread long distances, it has the potential to wipe out ‘ōhi’a lehua across the entire state. If ‘ōhi’a lehua disappears, it will lead to a collapse of the Hawaiian watershed and radically change the ecosystem.

How the Hawaiian People Care for ‘Ōhi’a Lehua

Scientists, researchers, and native Hawaiians are working together to ensure the long-term health and resilience of ‘ōhi’a and Hawaii’s native forests by mitigating the spread of Rapid Ohia Death. Hawaii’s Forest Service monitors the land to track the spread of ROD and mortality of trees, has developed sanitation and wound-sealing treatments, and collaborates with hunters and game managers to reduce disease transmission. Scientists rigorously test ‘ōhi’a trees to understand the disease cycle, find out how it can be broken, and to identify trees resistant to the infection that could be used in potential reforestation efforts.

To prevent the spread, Hawaii has announced quarantine restrictions, travel alerts, and sanitation rules. If you are shipping vehicles between islands, you should clean the entire understory with strong soap to remove all mud and dirt from the tires and wheel wells. People who go into ‘ōhi’a forests are advised to avoid breaking branches or moving wood around, to clean their shoes and clothes, and to decontaminate any tools used with alcohol or bleach to kill the fungus. Even hula practitioners are forgoing the use of ‘ōhi’a lehua.

Orange ‘ōhi’a lehua blossom (Image Credit: Joan Wasser via National Park Service)

Mālama the ‘āina

Mālama the ‘āina is a phrase that means to care for and honor the land. ‘Ōhi’a lehua is a wonderful representation of the interconnection between people and nature and I hope learning about this beautiful tree has encouraged you to appreciate the relationship we have with the Earth and what the natural world does for us.

Remember, if you take care of the land, it will take care of you.

Abigail

Abigail Gipson is an environmental advocate with a bachelor’s degree in humanitarian studies from Fordham University. Working to protect the natural world and its inhabitants, Abigail is specifically interested in environmental protection, ecosystem-based adaptation, and the intersection of climate change with human rights and animal welfare. She loves autumn, reading, and gardening.

Sources and Further Reading:

What Mediterranean tree is uniquely equipped to withstand wildfires with armor-like bark and high, out of reach, branches?

The stone pine!

The stone pine in Casa de Campo, Madrid. (image by author)

In his 1913-1927 novel, In Search of Lost Time, French writer Marcel Proust described the power of a soft, buttery madeleine cookie dipped in tea to transport the story’s narrator back to his childhood, unlocking a flood of vivid memories, emotions, and senses. Since then, the term “Proustian memory” has come to describe the sights, smells, sounds, or tastes that bring us back to a particular place in time, one that reminds each of us that we are home.

This is how my partner talks about the stone pine (Pinus pinea) in Spain. Raised in Madrid, she moved to the U.S. when she was twenty-three. For the next decade she’d go long stretches without returning home (blame grad school, work, a global pandemic, and high airfare).

But on those occasions where she was able to return home for a visit, before that first sip of cafe con leche, it was the stone pines flickering past the taxi cab window that brought her back to the youth she’d spent running beneath them, and told her soul that she was home.

There are few markers more reliable than the stone pine to remind you that you are in the Mediterranean. Its branchless trunk rises 25-30 meters from the dry ground. Deep grooves run up the thick, rugged bark in shades of rust and ash-gray. It is bare all the way up to a rounded crown that seems to hover above the landscape. Branches bearing clusters of slender needles splay out horizontally and cast large soft shadows on the ground, giving the tree its nickname, the parasol (umbrella) pine. Its high canopy offers nesting sites and vantage points for many birds of the Med, like Eurasian Jays and Red Kites.

The stone pine’s unique silhouette foreshadows its individuality among its relatives in the genus Pinus.

stone pine bark detail. (Photo by dmcd25)(CC-BY-NC via iNaturalist)

The Parasol Pine

It is a resilient tree with few natural predators. High branches keep its cones away from most ground-dwelling herbivores, and that hardy bark helps shield against both prying insects and wildfire, perhaps its most common threat in the Mediterranean. The clustering of branches high above the brush also helps it withstand fire events more successfully than other species in the area. That said—it’s important to understand that pests (like the pine tortoise scale) and runaway fires do remain serious threats, even if the stone pine is better prepared to meet them.

The tree also stands apart from other species of pine in its lack of hybridization—that is, its failure to crossbreed with other pine species, despite existing in close proximity. It does not demonstrate a tendency to interbreed with its neighbors like Pinus halepensis (Aleppo pine) or Pinus pinaster (maritime pine), and that is unusual among pines. It’s really just out here doing its own thing.

This pattern of genetic isolation is a product of circumstances. The stone pine’s pollination window doesn’t often line up with other species and, even when they do, the tree’s genetic makeup has remained distinct enough (while others have hybridized) that fertilization is increasingly improbable.

And unlike other pine species, stone pine seeds are not effectively dispersed by the wind, perhaps contributing to this isolation. Instead, they rely on the few animals that can reach them, particularly birds, to shake them free and drop them elsewhere.

Digging Deeper

I hope we’ve established that the stone pine is one tough, rugged cookie, designed from the root up to thrive in a variety of ecosystems around the Mediterranean. But what’s going on below the surface?

To really understand any tree, you’ve got to look down. When we talk about “siliceous” soils, we’re talking about soils that are made up mostly of silica—essentially a mineral of silicon and oxygen that comes from rocks like quartz and sandstone. These soils are characteristically sandy and drain water quickly, but offer fewer nutrients—making them less fertile and more inhospitable for many trees. They also tend to be more acidic.

On the other half of the pH scale (which measures the acidity of acids on one end, and alkalinity of bases on the other) are what are known as “calcareous” soils—that is, soils rich in calcium carbonate from sources like limestone or chalk, but light on most other important nutrients.

Understanding pH and soil. *Ann McCauley* et al. 2017, Montana State University

Both of these types of soil are found along the rocky Mediterranean. And while its preference is for the former, more siliceous soils, the stone pine does well in both. In fact, it’s this ability to thrive in these rocky soils that earned the tree its name, the stone pine. Of course, the tree’s deep roots alone are not always enough to survive in these nutrient-deficient soils. Like other pines around the world, Pinus pinea benefits from ectomycorrhizas, the symbiotic relationship between the tree and fungi in the ground that help facilitate nutrient exchange in soils where they are harder to come by. It’s a fascinating relationship that certainly deserves its own essay, but it is important to understand the critical role Ectomycorrhizal fungi (EMF) play in maintaining thriving forest ecosystems. They form mutually beneficial relationships with trees, where the fungi exchange those coveted soil nutrients for carbon compounds produced by the trees during photosynthesis. This natural partnership supports nutrient cycling and enhances tree health and growth, allowing pines just like the stone to survive under more challenging soil conditions.

Explore visualizations of how Ectomycorrhizal fungi support forest growth.

In the course of human events

We know quite a bit more about where the stone pine is, rather than where it’s from. Pinpointing its native range has proven difficult because the tree has been harvested, traded, and replanted by human since prehistory—first for their edible pine nut seeds, then by later civilizations like the Romans for their ornamental status. Even today, it is common throughout the region to find a street or garden lined with the distinctive tree.

Today, pine nuts from the stone pine remain big business, and their cultivation has been seen as an alternative crop in regions where the arid soil would make other agricultural endeavors too difficult.

Pine nuts served on a dish of roasted peppers. Via Pexels.

I’ve realized there is more to learn about the stone pine than I could ever hope to fit on a page. In my naivety or ignorance, I did not expect that. Its deceptively simple silhouette belies a complex story of resilience, symbiosis, and ancient history and, for at least one Spaniard, a reminder that she’s home.

Brendan began his career teaching conservation education programs at the Columbus Zoo and Aquarium. He is interested in how the intersection of informal education, mass communications and marketing can be retooled to drive relatable, accessible climate action. While he loves all ecosystems equally, he is admittedly partial to those in the alpine.

Sources and Further Reading:

Creature: Mycelium Connections

Featured Creature: ‘Ōhi’a Lehua