Family: Fabaceae

Acacia crassicarpa is a fast-growing tree native to southern New Guinea, northern Queensland, and the Torres Strait islands. It is valued in forestry for its wood and ability to improve soil fertility through nitrogen fixation. This species grows best in warm, humid lowland climates, often colonizing poor or degraded soils after disturbance. It is light-demanding and thrives in open areas, making it successful as a pioneer tree in its native range.

Outside its native habitat, A. crassicarpa has shown signs of invasiveness. It has naturalized and spread in disturbed areas of the Cook Islands and is considered a disturbance weed. Its hard-coated seeds form a persistent seed bank, and dispersal may occur through animals and water. The tree can also tolerate fire and quickly recolonize after disturbance. While it is not known to form dense thickets or invade intact forests, its ability to spread in open sites and alter soil conditions makes it a species to watch closely.

High Risk Traits:

• Naturalized and spreading on disturbed sites in the Cook Islands
  
• Disturbance weed (thrives in open and degraded areas)
  
• Unpalatable to livestock (but not poisonous)
  
• Nitrogen-fixing tree that can alter soil chemistry
  
• Seeds have a hard coat and form a persistent seed bank (dormancy)
  
• Seeds likely dispersed by animals (gut passage survival) and possibly by water
  
• Capable of natural hybridization with related Acacia species
  
• Can tolerate fire and colonize post-fire or post-disturbance environments
  
• Allelopathic effects observed in laboratory studies (inhibits growth of other plants)
  
• Produces viable seed and begins reproducing relatively early (4–5 years)
  
• Known to host plant pests and pathogens (though not major ones)

Low Risk Traits:

• Limited climate range (lowland tropics, coastal and humid areas)
  
• Does not form dense thickets
  
• Not shade tolerant (requires open, sunny areas)
  
• No evidence of spread by vegetative means (relies on seed)
  
• Seeds are relatively large and not adapted for wind or external animal dispersal
  
• Not a recognized agricultural or forestry weed
  
• No evidence of toxicity to animals or humans
  
• Effective natural enemies may occur locally (e.g., specialist rust fungi)