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Crack willow

Braided River Status

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Crack willow (Salix fragilis) is a deciduous tree that can grow up to 25 m tall. While their branches don’t droop like weeping willows, they break off easily with an audible ‘crack’. The leaves are narrow and lance-shaped, often with bright red swellings on them. They flower around the same time as the leaves re-appear in Spring. The yellow-green flowers are up to 7.5cm long and 1cm across. Not fruit is formed as there are only male plants in New Zealand. The roots form dense mats.

Crack willow

Crack willow

Why is it a problem?

  • Grows rapidly, creating dense thickets
  • Very tolerant of flooding, can grow in a wide range of temperatures, and in semi-shaded areas
  • Quickly replaces native species along waterways and forms vast dense (often pure) stands along channels
  • Stabilises braided river gravels, preventing the natural re-shaping of channels during freshes, changing the entire structure and flow of waterways and creating an environment completely unsuited to endemic river birds, reptiles, and plants (see research: “Crack willow fails to provide the same resources for these animals as the native counterpart… Invasion of riparian zones by crack willow has a detrimental effect on these valuable ecosystems!”
  • Absorb so much water that river levels can drop and disappear altogether in places
Crack willow branches fallen into water sprouting

Crack willow branches and root suckers sprouting

How is it spread?

  • Even the smallest stem fragments can take root anywhere that’s damp, and are readily spread downstream
  • Root suckers spread locally
  • Cut stumps regrow rapidly
  • Planted intentionally on stream and river banks to stabilise banks and in damp places, to absorb water

Conservation activities

More information