Family: Dicksoniaceae

Soft tree fern is an invasive plant that’s native to Australia and Tasmania. While it thrives in a broad range of climates, the higher elevation wet forests of the Hawaiian Islands are most at risk. The shade tolerance and long-distance spore dispersal are a dangerous combination for the native forests. 

In the 19th century, Soft tree fern was planted in a botanical garden in Sri Lanka. Today, it has formed dense thickets and has spread to an area of over 48 km2 – a substantial invasion. 

It is slow-growing and takes many years to reach reproductive maturity. However, when it does make fertile spores, it does so in massive quantities. A single frond produces as many as 750 million viable airborne spores! Its ability to spread via wind is astronomical – 500 to 800 km is the potential range. It spreads rapidly when fertile fronds are produced. There are few barriers to the dispersal of this species.

Description and Dispersal:

• Dicksonia antarctica is the largest species in the genus
  
• Grows up to 15m tall
  
• Small round sori
  
• Large dark green roughly textured fronds
  
• The stout trunk is densely covered in matted, brown aerial roots

High Risk Traits:

• Thrives in temperate & sub-tropical cool climates
  
• Grows in a variety of habitats, & elevation range exceeds 1000 m, demonstrating some environmental versatility
  
• Naturalized in Britain, & the Azores
  
• Environmental weed
  
• Other Dicksonia species have become invasive
  
• Potentially allelopathic
  
• Young fronds may contain toxins
  
• Shade tolerant
  
• Grows on many soil types (provided adequate moisture)
  
• Forms extensive stands in native range
  
• Capable of inter-gametophytic selfing
  
• Produces 1000s of wind-dispersed spores
  
• Can reproduce vegetatively
  
• Tolerates & will resprout after cutting or fires

Low Risk Traits:

• Would probably only threaten higher elevation ecosystems in tropical islands
  
• Unarmed (no spines, thorns or burrs)
  
• Palatable to ungulates and other browsing animals
  
• Ornamental
  
• Slow growth rate and reaches maturity after 20+ years