Family: Aquifoliaceae

Holly is an invasive tree in Hawaii that is native to Europe, Northern Africa, and Western Asia. Even in its native range, Holly makes dense stands that prevent other species from growing.

Before Hakalau Forest National Wildlife Refuge was established, privately owned ranches managed the land. One hundred fifty years of ranching, logging, and other human disturbances, transformed the area from a diverse native wonderland to grassy fields void of trees. Aggressive invasive species like Holly replaced the array of endemic Hawaiian plants. Today, Holly is the ‘highest priority target invasive plant species’ slated for eradication. With help from the Big Island Invasive Species Committee, the refuge actively works to eradicate this plant. 

Eradication is difficult due to Holly’s reproduction mechanisms. It reproduces vegetatively aggressively. Broken pieces in contact with the ground or leaf litter grow into a separate tree. Horizontal roots sucker far from the parent plant. Cut stumps will coppice. Low hanging branches root into the ground and grow into a new tree. It produces copious amounts of bird-dispersed seeds.

Currently invasive in Washington state, Oregon, California, British Colombia, and upcountry Maui consider Holly to be invasive.

Description and Dispersal:

• Pyramid-like, conical tree reaches 15 to 50 feet tall.
  
• Densely packed branches make up a 15-foot spread.
  
• Thick, bright green, glossy leaves have sharply pointed teeth, pointed alternatively upward and downward, along wavey margins.
  
• Off-white flowers are small and inconspicuous yet sweet-smelling.
  
• Bright red drupes (berry-like fruit) stand out among the green foliage.

High Risk Traits:

• Broad climate suitability
  
• Grows, and able to naturalize in, regions with subtropical climates
  
• Naturalized on Maui and Hawaii islands, and elsewhere
  
• An environmental weed, forming dense stands that outcompete native vegetation
  
• Other species may be weedy
  
• Spinose leaf margins
  
• Berries mildly toxic to animals and people
  
• Shade tolerant
  
• Tolerates many soil types
  
• Forms dense thickets
  
• Reproduces by seeds and vegetatively by suckering
  
• Seeds dispersed by birds, other frugivorous animals, and intentionally by people
  
• Prolific seed production in larger trees
  
• Seeds form a persistent seed bank (up to three years)
  
• Resprouts and coppices after cutting and fires

Low Risk Traits:

• Palatable foliage
  
• Dioecious (and not self-compatible)
  
• Reaches maturity in 5-12 years
  
• Herbicides may provide effective control