Wildfires in Hawaiʻi used to be extremely rare as the only sources of ignition were eruptions and dry lightning strikes. Therefore, our native ecosystems are especially vulnerable to fire disturbance. Unfortunately, modern land use change has resulted in the extensive spread of fire-prone grasses and shrubs, which continue to perpetuate the grass-fire cycle in our islands. Additionally, modern amenities like electricity, vehicles, and cigarettes, have resulted in more than 1,000 ignitions and over 20,000 acres burned each year in Hawaiʻi.
Key Terms (Click to expand)
- Fuel: Any live or dead plant materials that provide energy to the fire, such as grasses and leaf litter. Fuel is the only component of the fire behavior triangle that property owners can influence.
- Fuels management: Any method of altering vegetation to reduce hazardous wildfire conditions.
- Fire-prone plant: Often flammable plants that can ignite easily and burn intensely. Some examples include: fountain grass, koa haole, and eucalyptus.
- Fire-resistant plant: Plants that do not readily ignite nor provide significant fuel and lessens fire intensity. Fire resistance is influenced by a plant’s leaf moisture content, presence of dead material, and the chemical content of the sap.
- Green firebreak: A strip of fire-resistant vegetation planted strategically to slow or stop the spread of wildfires, especially near structures.
Fuels management is focused on reducing the following:
- Ignition potential: The probability that vegetation will combust and carry fire.
- Rate of spread: The speed at which fire moves through fuels over the landscape.
- Fire intensity: The energy released by the fire, commonly measured as fire temperature or flame length.
Importance of Fuels Management
The devastating 2023 Lahaina wildfire burned over 2,000 acres, killed 101 people, destroyed over 2,000 homes & businesses, and resulted in an economic loss in the billions. All of which made this recent fire the worst natural disaster in Hawaiʻi history and the deadliest U.S. wildfire in over a century. This tragic event has since ignited local interest in transforming hazardous vegetation.
To begin this effort, the Pacific Fire Exchange (PFX) sought to provide information on fire-resistant plant species to replace fire-prone species on the landscape. This is because fuels management is critical to minimize hazardous wildfire conditions within tropical grasslands and savannas, where people tend to live. Fire-resistant plants within green firebreaks can disrupt fire-prone grasses, lower fire intensity, and slow the rate of wildfire spread. To learn more about green firebreaks, check out this PFX Quick Reference Guide and Tips for Firewise Landscaping.
So, PFX evaluated 30 native and non-native plants based on (1) whether the species was commercially available or easily propagated and (2) minimal maintenance and care. This is to ensure higher rates of plant survival as we don’t want green firebreaks to become a fire hazard themselves. The following list spotlights 10 pono plants to use in your green firebreak, but you can view all of the other evaluated plants here.
DISCLAIMER (Click to expand)
The following list has no particular order, but serves to highlight a variety of assessed plants. Read more about these plants on plantpono.org to determine if your property is right for a certain plant. It is important to note that the use of green firebreaks does not prevent the spread and containment of all wildfires but rather creates safer conditions with the help of emergency response. In prolonged drought, low humidity, and high winds, any vegetation can burn. For more information on how to make your home more wildfire-resistant, check out this awesome article featuring Nani Barretto of the Hawaiʻi Wildfire Management Organization.
1. Kou (Cordia subcordata)
Kou trees are relatively small and make an excellent shade tree. These easy-to-grow, hardy trees have bright orange flowers and non-invasive roots. The showy flowers of the kou are perfect for stringing into a beautiful lei. This tree is drought, wind, and salt tolerant, making it a great option for drier and coastal areas. The floating seeds of kou could’ve easily traveled on the waves to Hawaiian shores as well as onboard waʻa (canoes) as kou wood was prized for containers. Kou wood was actually preferred over koa in old Hawaiʻi because it could be easily carved with non-metal tools. If you cannot find this plant at the nursery, you can collect the white fruits and propagate from seed or transplant a volunteer seedling from under your favorite kou tree.
2. ʻŪlei (Osteomeles anthyllidifolia)
ʻŪlei is a native sprawling shrub within the rose family. Delicate white flowers stand out among the dark green foliage. The dense growth of ʻūlei shades out the weeds well. The globe-shaped fruit is off-white and encapsulates 3-4 wedge-shaped seeds. ʻŪlei grows well in a wide range of conditions, and it’s drought tolerant once established. However, this is a slow-growing species that requires regular watering to establish. Traditionally, the woody stems of ʻūlei were transformed into handles for scoop nets, spears, and musical instruments. Propagation is by seeds or vegetatively by cuttings. Few pests will attack this plant, making it a good low-maintenance plant to grow in your green firebreak.
3. Pōhinahina (Vitex rotundifolia)
A sea of silver contrasted with clusters of bell-shaped purple flowers. In full bloom or not, pōhinahina is a striking indigenous sprawling shrub. A tried and true native plant, pōhinahina is one of the hardiest native plants, especially in hot and dry areas. Heavy traffic, pollution, wind, sand, and salt don’t bother this plant. Pōhinahina is a prolific groundcover making it great for erosion and weed control. Their fragrant silvery foliage continues to be used in lei, wreaths, and other floral arrangements. Pōhinahina has shown to be largely unaffected by fire despite being close (within 10 feet) to flames, making this plant a great candidate for companion planting within green firebreaks.
4. ʻĀweoweo (Chenopodium oahuense)
ʻĀweoweo is a hardy endemic shrub that grows from the ocean to high elevations, usually on the leeward sides. Mature plants range from 3 to over 10 feet! As a goosefoot family member, the leaves are three-lobed. Velvety hair gives them a silvery appearance, blue-green in color. Like the ʻāweoweo fish, the red-streaked stems add a subtle flash of color, and the leaves are weakly scented with a fishy odor when crushed. Once established, ʻāweoweo is maintenance-free! These plants grow quickly, seed plentifully, and germinate readily on its own. Out-planted individuals need to be watered to become established. Sow many if propagating by seed.
5. Noni (Morinda citrifolia)
Noni is a relatively small evergreen tree and a supreme canoe plant. This tree is well-known across Pacific Island societies as a significant source of traditional medicine. The glossy green leaves of the noni are striking in any landscape. However, be careful where you plant this tree, as the ripe white fruit can make for a foul-smelling litter. Mature trees can tolerate drought, shade, fire, waterlogging, salt spray, and high winds. Therefore, noni is a great choice for fire-risk areas, especially as they can regenerate after fire by sprouting new foliage through roots or stems. This rapid ability to regenerate after severe pruning or damage makes this low-maintenance tree perfect for any green fire break.
6. Kamani (Calophyllum inophyllum)
Kamani is a coastal shade tree that hosts beautiful clusters of sweet-smelling white flowers and thick paddle-shaped leaves. Kamani thrives in the hot sun and can become a prolific seed producer once mature. The large amounts of litter and sometimes intrusive roots can make this tree a little hazardous where people walk, but it would be perfect in a low-maintenance green firebreak away from the property. This canoe plant is prized for its versatility. Flowers were used to scent kapa, wood for food vessels, nuts for whistles and lei, and oils for medicine and waterproofing. This tree quickly grows from seed or volunteer seedlings. If you live below 1600 ft. elevation, then this tree is perfect for your property.
7. Kukui (Aleurites moluccana)
Kukui is our state tree and is well known for its silvery-green foliage. Leaves are shaped like pig heads, and white flowers appear in terminal clusters. The green fruits mature brown and contain 1-2 seeds with hard rough shells. Traditionally, Hawaiians utilized the wood, nut shells, seeds, bark, and even sap! This tree is fast-growing, loves disturbed soils, and tolerates a wide variety of environmental conditions. However, watch out for invasive Queensland Longhorn Beetles, which are known to attack and kill mature kukui trees. Kukui can be easily propagated from its plentiful seeds and volunteer seedlings. Although the nuts are flammable and were used to make bright torches, kukui trees still provide protection from fire as they store lots of water in their trunks and provide thick shade to the leaf litter, keeping it moist and cool.
8. Mango (Mangifera indica)
Mango trees are beloved non-native trees from southern Asia. These trees grow up to 30 meters tall with a long taproot up to 8 meters deep. This long-lived tree has fruits enjoyed by nearly everyone, but be sure to pay attention to the rainfall range of your specific mango variety. Additionally, keep an eye out for common diseases like anthracnose and powdery mildew. Mango trees are robust in full sun and tolerant to drought for up to 8 months, which makes them excellent for green firebreaks. Once mature, these trees can regenerate after fire. Therefore, adding mango to your firebreaks provides excellent shade to limit grassland fuels, while producing a sweet summer treat!
9. Monkeypod (Samanea saman)
Monkeypod is a wonderful shade tree with an umbrella-shaped canopy and showy pink-tipped flowers with many stamens. Its compound leaflets with diamond-shaped leaves fold up on rainy days and at night. Monkeypod is known for its sticky brown seed pods, which are said to taste like licorice. This non-native tree was introduced to Hawaiʻi in 1847 from Mexico. The wood is used in woodworking and the seeds are good fodder for hooved animals. Today, monkeypods are used extensively in lowland streets, parks, and pastures. In dry areas of Fiji, monkeypods are usually the last line of defense against fires in a sea of fire-prone grasses and reeds. Therefore, this species is a proven suggestion for any firebreak.
10. Shower tree (Cassia species)
There are several introduced pono species of shower trees present in Hawaiʻi, including Cassia bakeriana, Cassia fistula, Cassia javanica, Cassia grandis, and Cassia roxburghii. All shower trees are in the Fabaceae family, which means they are nitrogen-fixers, host compound leaves alongside pea-shaped flowers, and form legume fruits. These large, shady trees are commonly used in parks and as street trees. Shower trees do well in dry, hot climates with well-draining soils and can continue to produce profuse flowers in yellow, pink, and red. They remain low maintenance and tolerate wind, pests, and weeds. Shower trees are usually completely or partially deciduous, which makes them fire-resistant. Deciduous trees tend to have higher moisture content in the leaves, thicker bark, and lack of flammable oils.
