Family: Fagaceae

Origin, Description & Uses
Quercus ilex (holm oak, evergreen oak, holly oak) is a long-lived evergreen tree native to southern and central Europe and the Mediterranean region. It is a dense, slow-growing oak that can develop into a large shade tree with a broad, rounded crown. The leathery, dark green leaves are somewhat holly-like in appearance, giving the species one of its common names. Holm oak is widely planted in landscaping and urban environments for its durability, drought tolerance, and ability to provide deep shade. It has also been used historically for timber, fuelwood, and for its acorns, which can serve as wildlife forage.

Risks & Threats
Although Quercus ilex is not known to be naturalized in the Hawaiian Islands, it does possess traits that are cause for concern. It is highly adaptable to dry conditions, produces abundant seeds (acorns) that can be spread by animals, and is capable of forming dense stands that suppress understory vegetation and reduce biodiversity. These characteristics can increase its potential to establish and spread in suitable habitats, particularly in dry to mesic environments. Because of these traits, ongoing evaluation is needed to determine whether it could negatively impact Hawaii’s ecosystems, and caution is recommended to help ensure it does not become invasive in the state.

High Risk Traits:

• Elevation range exceeds 1000 m, demonstrating environmental versatility
  
• Naturalized in British Isles, escaped in New Zealand
  
• Possible negative environmental impacts in Britain
  
• Other Quercus species have become invasive
  
• Self-allelopathic (may affect other plants)
  
• Spinose leaves
  
• Alternative host of Phytophthora ramorum, pathogen causing sudden oak death
  
• Flammable. May increase fire risk
  
• Shade-tolerant
  
• Tolerates many soil types
  
• Forms dense stands in native range
  
• Reproduces by seeds and root suckers
  
• Hybridizes with other Quercus species
  
• Seeds dispersed by seed hoarding birds, rodents and intentionally by people
  
• Potential for prolific seed production (mast seeder), but densities unspecified
  
• Able to coppice

Low Risk Traits:

• Palatable to browsing animals
  
• Non-toxic
  
• Ornamental
  
• Self-incompatible
  
• Reaches maturity in 8+ years
  
• Recalcitrant seeds unlikely to form persistent seed bank