Family: Rosaceae

Rubus ulmifolius (Himalayan blackberry) is a robust, thorny shrub native to Europe that forms dense, impenetrable thickets capable of outcompeting native and agricultural plants. Its arching, prickly canes can grow several meters long, rooting where they touch the ground and creating extensive, tangled mats. This species is naturalized on Oʻahu and Maui and is potentially naturalizing on Hawaiʻi Island. Like other invasive blackberries, it thrives in disturbed sites, pastures, and along forest edges where it can quickly dominate the understory and prevent regeneration of native vegetation.

Himalayan blackberry spreads vigorously by seed, birds, and vegetative means, making it extremely difficult to control once established. Its dense growth alters habitat structure, limits access for wildlife and people, and increases fuel loads that contribute to wildfire risk. While the plant produces edible fruit, the ecological and management costs far outweigh any benefit. Land managers and residents are encouraged to avoid planting or spreading this species.

High Risk Traits:

• Broad climate suitability
  
• Naturalized beyond its native range (e.g., Hawaii, western US, Australia)
  
• Agricultural and environmental weed (forms impenetrable thickets)
  
• Weedy congenerics (other invasive Rubus species exist)
  
• Armed with prickles
  
• Creates a fire hazard due to dense litter
  
• Tolerates a wide range of soil conditions
  
• Forms dense, monospecific thickets
  
• Multiple reproductive strategies (viable seeds, self-compatibility, vegetative fragmentation)
  
• High seed dispersal (by water, birds, and humans; survives gut passage)
  
• Prolific seed production (7,000-13,000 seeds/m²)
  
• Forms a persistent seed bank
  
• Tolerates and resprouts after fire or mutilation

Low Risk Traits:

• Not allelopathic or parasitic
  
• Palatable to livestock (e.g., goats, sheep)
  
• Not toxic to humans or animals
  
• Not shade tolerant
  
• Can be controlled with herbicides