Family: Oleaceae

Origin, Description & Uses:
Tropical ash (Fraxinus uhdei) is a fast-growing tree native to Mexico and Central America. It is widely planted in tropical and subtropical regions as a shade tree, windbreak, and ornamental due to its tall stature, smooth gray bark, and compound leaves with multiple leaflets. The tree produces clusters of small flowers followed by winged seeds that are easily dispersed by wind. In Hawaiʻi, it has been used in landscaping and reforestation efforts because of its rapid growth and ability to establish in a variety of soil types.

Risks & Threats:
Tropical ash is naturalized on Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Maui, and Hawaiʻi Island, and possesses several traits that are cause for concern. It produces abundant wind-dispersed seeds, grows quickly, and can establish dense stands that outcompete native vegetation. These characteristics allow it to spread into disturbed areas as well as more intact ecosystems, where it may alter forest structure and reduce biodiversity. Because of its aggressive growth and ability to dominate landscapes, Fraxinus uhdei could detrimentally impact tropical island ecosystems if not properly managed.

High Risk Traits:

• Naturalized: Kauai, Oahu, Molokai, Lanai, Maui, Hawai`i
  
• Environmental weed: Disruptive to native ecosystems in Hawai`i; alters forest structure, light penetration, decomposition, and nutrient cycling
  
• Congeneric weeds: Other Fraxinus species are invasive elsewhere
  
• Shade tolerant: Can regenerate in understory
  
• Forms dense thickets: Creates nearly monotypic stands that exclude native species
  
• Produces viable seed: Readily reseeds
  
• Wind-dispersed seeds: Samaras facilitate long-distance dispersal
  
• Water-dispersed propagules: Spreads along watercourses
  
• Persistent seed bank: Seeds may remain viable for up to eight years
  
• Tolerates mutilation: Coppices and regenerates rapidly after cutting
  
• Intentionally introduced: Widely planted as an ornamental and forestry tree
  
• Host for pests: Susceptible to ash whitefly (Siphoninus phillyreae)
  
• Broad climate suitability: Tolerates a wide range of altitudes, temperatures, and rainfall regimes

Low Risk Traits:

• Not toxic to animals or humans
  
• No fire hazard: No evidence of increasing fire risk
  
• Not a climbing or smothering growth habit: A free-standing tree
  
• Dioecious: Requires both male and female plants for seed production
  
• No vegetative fragmentation: Regenerates primarily by seed
  
• Not bird-dispersed
  
• Controlled by herbicides: Effective management with cut-stump and ring-notching methods