Family: Salicaceae

Origin, Description & Uses
Salix nigra (black willow, swamp willow) is a deciduous tree native to eastern Canada through the United States and into Mexico. It typically grows in lowland wetlands such as riverbanks, floodplains, and swampy areas, where it can form dense stands. Black willow is known for its long, narrow leaves, rough bark, and fast growth in wet soils. It has been used historically for a variety of purposes, including erosion control along waterways, restoration of riparian habitats, and as a source of flexible wood for basketry and light construction. It also plays an important ecological role in its native range by stabilizing stream banks and providing habitat for wildlife.

Risks & Threats
Although Salix nigra is not known to be naturalized in Hawaiʻi, it possesses traits that are cause for concern. Its strong ability to spread in wet environments, rapid growth, and capacity to reproduce readily from seeds and broken stem fragments could allow it to establish in suitable riparian habitats if introduced. In Hawaiʻi’s sensitive watershed ecosystems, a species like black willow could potentially alter stream flow, compete with native vegetation, and change habitat structure along waterways. Ongoing evaluation is needed to determine its potential impact under local conditions, and caution is recommended to ensure it does not negatively affect Hawaiʻi’s native ecosystems.

High Risk Traits:

• Broad climate suitability
  
• Naturalized in Australia
  
• Regarded as an environmental weed of riparian environments in Australia
  
• Other Salix species have become invasive in Australia
  
• Tolerates many soil types (as long as moisture content is high)
  
• Able to form pure stands
  
• Produces viable seeds
  
• Able to hybridize with other Salix species
  
• Able to sucker and spread by vegetative fragments
  
• Seeds dispersed by wind and water, and intentionally by people
  
• Prolific seed production in native range
  
• Able to coppice and resprout after cutting or fires

Low Risk Traits:

• A temperate species that may only pose a threat to higher elevations of tropical islands
  
• Unarmed (no spines, thorns or burrs)
  
• Palatable to a variety of browsing animals
  
• Non-toxic to animals and people (although pollen may be an allergen)
  
• Ornamental
  
• Shade-intolerant
  
• Dioecious (and therefore self-incompatible)
  
• Reaches maturity in 10+ years
  
• Seeds lose viability quickly
  
• Herbicides provide effective control