poddy mullet
30-05-2010, 02:07 PM
Many of the best fishing spots throughout the central west region have Willow trees along the banks, however the truth about Willows is that they are causing major problems for native fish and the river in general.
Willows were planted by European settlers for several reasons which include aiding paddle-steamer navigation by marking the main channels in Murray River during the 1860s, and the stabilisation and prevention of erosion of the banks which occurred due to the clearing of riverside and catchment vegetation. Willows were also introduced to the banks of Australian rivers for their aesthetic appeal.
The Willows along the Macquarie do provide a small amount of food and habitat for some river life, but they compete with native gums for water, and some plants, fish, and animals such as platypus and tortoises are discouraged by their dense shade.
Many native fish, such as the Murray Cod, rely on snags provided by River Red Gum branches for spawning sites and shelter, and as Willow tree limbs break down very quickly they do not provide sufficient snags for native fish to breed.
Willows also drop all their leaves at the end of autumn, which increases the organic load and nutrient levels in waterways. The leaves of Willow trees are also ‘soft’ and decompose very readily, far more quickly than our aquatic macro-fauna can process. The large load of organic material, coupled with rapid breakdown by microbes, results in an excessive release of nutrients into water systems, causing deterioration in water quality
The intense shading caused by many deciduous trees can prevent other flora from growing beneath them. The resulting lack of understory vegetation can render the banks of waterways prone to erosion. By contrast, in other situations willows may form dense mats of roots which extend out into streams and rivers, causing increased sedimentation. In severe cases this can cause a channel blockage and result in flooding upstream. Trees such as willows are also easily uprooted in floods, causing major blockages.
Willows also increase the river’s salinity problems as they only take water from the upper fresh layers, allowing salt to rise into the river, whereas red gums take 40–50 per cent of their water from these layers, helping to keep the saline water table low.
Willows were planted by European settlers for several reasons which include aiding paddle-steamer navigation by marking the main channels in Murray River during the 1860s, and the stabilisation and prevention of erosion of the banks which occurred due to the clearing of riverside and catchment vegetation. Willows were also introduced to the banks of Australian rivers for their aesthetic appeal.
The Willows along the Macquarie do provide a small amount of food and habitat for some river life, but they compete with native gums for water, and some plants, fish, and animals such as platypus and tortoises are discouraged by their dense shade.
Many native fish, such as the Murray Cod, rely on snags provided by River Red Gum branches for spawning sites and shelter, and as Willow tree limbs break down very quickly they do not provide sufficient snags for native fish to breed.
Willows also drop all their leaves at the end of autumn, which increases the organic load and nutrient levels in waterways. The leaves of Willow trees are also ‘soft’ and decompose very readily, far more quickly than our aquatic macro-fauna can process. The large load of organic material, coupled with rapid breakdown by microbes, results in an excessive release of nutrients into water systems, causing deterioration in water quality
The intense shading caused by many deciduous trees can prevent other flora from growing beneath them. The resulting lack of understory vegetation can render the banks of waterways prone to erosion. By contrast, in other situations willows may form dense mats of roots which extend out into streams and rivers, causing increased sedimentation. In severe cases this can cause a channel blockage and result in flooding upstream. Trees such as willows are also easily uprooted in floods, causing major blockages.
Willows also increase the river’s salinity problems as they only take water from the upper fresh layers, allowing salt to rise into the river, whereas red gums take 40–50 per cent of their water from these layers, helping to keep the saline water table low.