Family: Myrtaceae

Origin, Description & Uses
Eucalyptus paniculata, commonly known as grey ironbark, is a tall, long-lived tree native to eastern Australia. It is recognized for its deeply furrowed, dark grey to black “ironbark” bark and dense, durable wood. This species can reach impressive heights and produces clusters of white flowers that attract pollinators. Grey ironbark has been widely planted in tropical and subtropical regions, including Hawaiʻi, for forestry, windbreaks, erosion control, and ornamental purposes. Its exceptionally hard, termite-resistant timber is highly valued for construction, fencing, and heavy-duty applications.

Risks & Threats
In the Hawaiian Islands, grey ironbark is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Maui, and Hawaiʻi. This species possesses traits that are cause for concern, including the ability to spread beyond cultivation, tolerate a range of environmental conditions, and potentially outcompete native vegetation. Its dense canopy and leaf litter can alter soil conditions and reduce light availability, limiting the growth of understory plants. Additionally, like many eucalyptus species, it may contribute to increased fire risk due to its flammable oils and shedding bark. Because it is already established and capable of spreading, Eucalyptus paniculata could detrimentally impact tropical island ecosystems. It is recommended to avoid planting this species and instead choose a low-risk or native alternative better suited to Hawaiʻi’s unique environments.

High Risk Traits:

• Naturalized in Hawaiʻi: Present on Kauaʻi, Oʻahu, Molokaʻi, Maui, and Hawaiʻi.
  
• Invasive elsewhere: Category 2 invader in South Africa.
  
• Broad climate suitability: Tolerates wide range of climates, altitudes, and soils.
  
• Widespread introductions: Planted across multiple continents for forestry and timber.
  
• Congeneric weeds: Other Eucalyptus species are serious weeds.
  
• Unpalatable: Chemical properties deter grazing animals.
  
• Host for pests/pathogens: Supports generalist fungi and insects.
  
• Fire hazard: Accumulates heavy litter layer, increasing fuel load.
  
• Produces viable seed: Reproduces readily by seed.
  
• Hybridizes: Known to hybridize with other Eucalyptus species.
  
• Wind-dispersed: Small, light seeds dispersed by wind.
  
• Prolific seed production: Produces abundant seed.
  
• Coppices vigorously: Resprouts after cutting or damage.

Low Risk Traits:

• No spines or thorns.
  
• Not toxic to animals or humans.
  
• Not shade tolerant: Requires full sun.
  
• No vegetative reproduction.
  
• No persistent seed bank: Seeds lack long-term dormancy.
  
• Not dispersed by water, birds, or as a contaminant.