Family: Myrtaceae

Origin, Description & Uses
Eucalyptus microcorys, commonly known as Australian tallowwood, is native to eastern Australia, where it grows in coastal and subcoastal forests. It is a tall, long-lived tree that can reach over 100 feet in height, with a dense canopy of glossy green leaves and rough, fibrous bark on the trunk. Tallowwood is highly valued for its durable, termite-resistant timber, which has been widely used for flooring, decking, construction, and heavy outdoor applications. It is also planted as a shade and windbreak tree in tropical and subtropical regions, including parts of Hawaiʻi, where it has become naturalized on Kauaʻi, Maui, and Hawaiʻi Island, and is potentially naturalizing on Oʻahu and Molokaʻi.

Risks & Threats
Although Eucalyptus microcorys is considered low risk overall, its ability to naturalize in multiple Hawaiian Islands indicates some capacity for spread. Like other eucalyptus species, it produces abundant seeds and can establish in suitable disturbed habitats. However, it does not appear to aggressively invade native ecosystems or form dense monocultures that significantly displace native vegetation. Potential concerns include localized competition with native plants, increased fire risk due to the accumulation of leaf litter and oils, and changes to soil moisture dynamics. At this time, these impacts are considered limited, but continued monitoring is recommended, particularly in areas where the species is expanding beyond planted landscapes.

High Risk Traits:

• Naturalized on Kaua'i, Hawai'i and Maui
  
• Potentially Naturalizing on Molokai and O'ahu
  
• Widely introduced: Planted across multiple continents (Asia, Africa, Europe, Americas, Oceania).
  
• Congeneric weeds: Closely related Eucalyptus species are known weeds.
  
• Pest host: Host for Strepsicrates macropetana (Eucalyptus leafroller), a significant pest in plantations.
  
• Soil tolerance: Thrives in a wide variety of soils, including poor sands.
  
• Wind dispersal: Small, light seeds dispersed efficiently by wind.
  
• Prolific seed production: Produces 100,000–400,000 seeds per kilogram.
  
• Resilience: Tolerates mutilation (coppicing) and fire; growth unaffected by burning.

Low Risk Traits:

• Not a weed: No record of being a garden, agricultural, or environmental weed.
  
• No defenses: Lacks spines, thorns, or burrs.
  
• Non-toxic: No evidence of toxicity to humans or animals.
  
• No persistent seed bank: Seeds germinate quickly and do not remain viable in soil for over a year.
  
• No vegetative spread: Does not reproduce by vegetative fragmentation.