Why are Willows a problem?

Willows infest thousands of kilometers of waterways across southeast Australia and cause substantial social, economic and environmental impacts, including:

  • increased erosion and flooding and damage to nearby infrastructure:

Willows were originally planted along waterways to combat bank instability when river banks were cleared of native vegetation or over grazed. However it has been found that as they grow out into the stream with multitudes of stems that they obstruct and divert floods and subsequently erode riverbanks arround the root mass, particularly along small, narrow rivers.

  • reduced water quality:

In contrast to native evergreens, willows drop all of their leaves at once in autumn and so break down more quickly than leaves of native plants. This alters the temperature and oxygen content of the water.

  • reduced flow of water:

Willows growing with their roots in water can consume substantially more water then river red gums on the riverbank. Have a look at the results of the water usage studies carried out by ENIS -  CSIO.

  • less habitat available for fish, frogs, birds, insects and spiders:

 The dense summer shade cover of willows combined with their impenetrable root system greatly inhibits the growth of land and water plants.

Willow-lined reaches of rivers support significantly fewer insects, fish and birds when compared with reaches lined with native trees and shrubs.
Willow species roots grow into the aquatic environment, forming dense mats which, if growing in the vicinity of rocky habitats along the stream, will smother and fill all available rock crevices used by frogs like the Booralong frog for breeding.

reduced access to streams for fishing and aquatic activities:

Willows form dense root mats and stems that mat into the river, which in certain circumstances block access to the river bank and passage along the river bank for speedboats, canoes and rafts.

for more information on why willows are a problem I recommend reading section one of the Willows Management guide pages 5 to 9. The complete guide can be also be access and downloaded from the Weeds Australia Web site or you can order a printed copy of the manual from the National Willows Co-ordinator.

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