Containment species: BIISC is only working to manage this plant in specific areas
European holly (Ilex aquifolium) is symbolic and lucky in its native range – the right plant in the right place. Here in Hawaii, holly is bad luck for the native forest – the wrong plant in the wrong place.
In 1985, the Hakalau Forest National Wildlife Refuge was established as a critical habitat to preserve 27 endangered bird and plant species. Before the establishment of the refuge, the forest was grazed by cattle and used for logging. Pigs and cattle caused considerable damage to the native understory, paving the way for invasive species to colonize the area and replace the diverse array of endemic Hawaiian plants.
At some point during the ranching period, someone planted holly outside their home, and then it started to spread into the forest. Like the remnants of ranching that still litter the refuge, Holly is a foul testament to how humans play a part in altering landscapes.
In 2010, Hakalau managers identified it as “the highest priority target invasive plant species.” With help from the Big Island Invasive Species Committee, the refuge is actively working to eradicate this plant.
- Produces copious amounts of seeds, up to 120,000 in one year
- Seeds remain viable yet dormant in the soil for at least five years
- Grows in deep shade or open pasture
- Makes dense stands that outcompete native species
- Reproduces vegetatively and by bird-dispersed seeds
- 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
BIISC staff controlling Holly in a native-dominated forest.
What we do at BIISC
BIISC along with Hakalau Forest National Wildlife Refuge staff clear holly from the native forest.
Controlling European holly
For big trees, access to the trunk is difficult. The lower branches form a curtain of prickly foliage, firmly rooted in the ground and attached to the main stem. First, the lower limbs are cut, and to prevent new growth, they are uprooted manually. Next, forest technicians kneel on the thick carpet of sharp leaves and fell the tree with a machete or a handsaw. The stump is then treated with a small application of herbicide to prevent coppicing. BIISC technicians uproot small trees whenever possible, and all vegetation is hung off the ground or straddled between other trees to prevent vegetative regrowth.