Family: Casuarinaceae

Casuarina equisetifolia, commonly known as ironwood or Australian pine, is a fast-growing evergreen tree native to Australia, Southeast Asia, and parts of the western Pacific. Despite its pine-like appearance, it is not a true pine; instead, it has slender, jointed branchlets that resemble needles and tiny, scale-like leaves. Ironwood is highly tolerant of salt spray, wind, drought, and poor soils, making it popular worldwide for coastal windbreaks, shade, erosion control, and as a source of fuelwood and timber. Its ability to thrive in harsh coastal conditions has led to widespread planting in tropical and subtropical regions.

However, ironwood poses significant environmental risks where it has been introduced outside its native range. It spreads easily by wind-dispersed seeds and can form dense stands that crowd out native coastal plants, reducing biodiversity and altering natural ecosystems. Ironwood also changes soil chemistry through nitrogen fixation and produces thick leaf litter that can suppress the growth of other species. Its shallow root system may destabilize shorelines and contribute to beach erosion, threatening native coastal habitats and wildlife. Because of these impacts, ironwood is considered invasive in many areas, including Hawaiʻi, and its planting is discouraged in favor of native or non-invasive alternatives.

High Risk Traits:

• Highly invasive outside its native range, especially in coastal environments
  
• Produces abundant, wind-dispersed seeds that spread easily over long distances
  
• Rapid growth and early maturity, allowing it to outcompete native vegetation
  
• Forms dense monocultures that displace native plants and reduce biodiversity
  
• Allelopathic leaf litter that suppresses germination and growth of other species
  
• Nitrogen-fixing ability, which alters soil chemistry and favors further invasion
  
• High tolerance of salt, wind, drought, and poor soils, enabling spread in harsh coastal conditions
  
• Shallow root systems that can destabilize shorelines and contribute to erosion
  
• Difficult to control once established, with resprouting and seedbank persistence

Low Risk Traits:

• Limited shade tolerance compared to some forest trees
  
• Generally not invasive in its native range (Australia and nearby regions)
  
• Specific habitat preference (open, sunny, coastal or disturbed sites) may limit spread in intact forests
  
• Valued for specific uses (windbreaks, erosion control, timber, fuelwood) when carefully managed in appropriate settings