Silk oak (Grevillea robusta) is a large invasive tree. The common name is confusing; it is not in the oak family. Native to Australia, it was imported to Hawaii in 1851. Over a fifty-year period, 2.1 million silk oak trees were planted for forestry. Because it has broad climate adaptability, it has naturalized wherever it was planted. Today it is one of hawaiis most invasive horticultural plants.
Leaves and seeds drop in mass, creating a thick layer of debris. Strong roots lift and damage sidewalks, streets, and foundations. Brittle limbs are a hazard.
Description and Dispersal:
- A large tree, reaching a height of 75 feet or more
- Canopy has a pyramidal shape and a 25 for spread.
- Horizontal limbs and a thick trunk.
- Fern-like green leaves are divided into many lobes.
- Produces large clusters of brilliant yellow flowers.
- Black, leathery seed capsules follow the flowers.
High Risk Traits:
- Elevation range exceeds 1000 m, demonstrating environmental versatility
- Grows in tropical climates
- Naturalized in the Hawaiian Islands and several other locations worldwide
- Potential pasture weed
- Environmental weed
- Grevillea banksii also invasive
- Allergenic sawdust and pollen
- Tolerates many soil types
- Capable of forming dense stands
- Reproduces by seed
- Seeds dispersed by wind, water and intentionally by people
- Prolific seed production (densities unknown)
- Able to coppice and resprout after cutting
Low Risk Traits:
- Unarmed (no spines, thorns, or burrs)
- Palatable to goats and used as a livestock fodder
- Light-demanding (Shade-intolerant)
- Not reported to spread vegetatively
- Reaches maturity in 6+ years
- Herbicides may provide effective control