What happens when willows are removed?

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Shirley Henderson
Posts: 356
Joined: Sun May 06, 2007 4:03 pm
Location: Thirlmere

What happens when willows are removed?

Post by Shirley Henderson » Tue Apr 01, 2008 7:14 pm

Can you tell me what sort of information is available in regards to before and after effects of willow removal.
Before removal I hear nothing lives in the shade of the willow, excess nutrient release etc. etc.
After the willows have gone, is there improvements? What kind of information is there to read about the after effects of Willow removal.
thanks
Shirley

ColinJEly
Posts: 167
Joined: Fri Feb 15, 2008 1:50 am
Location: melbourne

What happens when willows are removed?

Post by ColinJEly » Thu Apr 03, 2008 8:25 am

Shirley
If they are Salix alba var caerulea, they make good cricket bats! :shock:

Cheers

Col.

duane
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Post by duane » Thu Apr 03, 2008 2:49 pm

Hi Shirley

This is a post from the Willows and Biodiversity blog.

This is a summary of a paper presented by Dr Michael Wilson of the Murray Darling Basin Commission. Dr Wilson was a Senior research scientist at the University of Ballarat in Victoria. He did his PhD on willows and ran postgraduate programs for 10yrs looking at the role of willows in Australian streams.

Willows: weeds of retention

Dr Michael Wilson
Sustainable Rivers Audit, Murray-Darling Basin Commission

Summary

The way materials, including organic matter, are retained, stored and transformed is at the heart of stream ecology. Retention, storage and transformation of soil, nutrients, salt, seeds and organic matter are also crucial to long-term farm productivity. A landscape view of retention is useful to those interested in ecology and production, and is highly relevant to understanding Natural Sequence Farming.
All but a few willow species are declared Weeds of National Significance and they line tens of thousands of kilometres of streams in south east Australia. They were once widely recommended for riparian planting and restoration, however now the same agencies advocate their removal. Whilst the policy has changed the fundamental biology of willows and their influence on stream function has not.
At this conference I will present ten years of research conducted by my PhD and honours students and myself. The key message is that retention rates of sediment, organic matter, nutrients and woody debris are greater in streams lined by willows than those lined by bare banks (pasture). Retention rates in willow-lined streams are similar to or sometimes greater than in streams lined by native vegetation in agricultural zones. Even more surprising is that this is true even for streams lined by native vegetation last cleared in the gold rush. The recovery from gold rush river metamorphosis in Central Victoria is very slow under native vegetation, even in low-disturbance forest reserves, compared to under willows. Our research has confirmed that high retention rates are largely due to willow root mats and entrapment of large woody debris.
We have studied numerous ecological parameters in willow, native and cleared reaches and we have seen the same overall pattern. The willow-lined streams we have studied in agricultural zones have high ecological and geomorphological values, often greater than those lined by native vegetation. Both native and willow lined streams have higher value than cleared streams. A canopy, regardless of whether it is willow or native, controls in-stream metabolism and temperature. Tree limbs and trunks supply woody debris and deep extensive root systems armour banks and shape the channel. There are also flow-on effects for stream biota, for example 80% of River Blackfish use undercut banks armoured by willow root mats as day time refuges in Birches Creek. Similar results have been found for platypus burrows in the Shoalhaven. Macroinvertebrate assemblages are more diverse and there is greater abundance in highly retentive root mats compared to bare banks or those lined by tea-trees, especially during tunes of high flow. The bugs and fish are taking advantage of the flow refuge provided by the root mats. These patterns are not surprising but are controversial because willows have been declared weeds and society finds it difficult to acknowledge benefits from weeds.
There are specific differences between willows and native trees (eg the palatability of leaves, seasonal patterns of light levels below the canopy, and litterfall timing). However, with the exception of those specifically related to light levels under a deciduous canopy, we have found these to be within the range found for native riparian species.
Clearing willows (or any other riparian tree cover) is not beneficial to in-stream ecological processes in agricultural zones. It is sometimes defended in that it clears the way for planting native vegetation. However, the clearing phase is destructive, recovery is slow and during the establishment of mature native forest retention rates and overall ecological values are low. New approaches are needed to establish the preferred forest without clearing ie using a successional approach. The fact that a stream ecologist and a farmer (Peter Andrews, Natural Sequence Farming) have independently arrived at the same conclusion in relation to willows is noteworthy. A good understanding of the ecological values associated with retention of materials, energy and nutrients in streams would compliment hydrological studies in Natural Sequence Farming systems and help shift public policy and perceptions away from simplistic approaches to weeds.

duane
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Post by duane » Thu Apr 03, 2008 2:53 pm

More info on willow removal

Taken from "Your experiences etc".....two opposing views below

A TALE OF TWO CITIES


Removing willows from LAUNCESTON rivers

When a city such as Launceston sits at sea level at the junction of two rivers — the North and South Esk - flooding is a constant threat. The great flood of 1929 made 4,000 people homeless and most bridges in the midlands were carried away.

Flood damage to city levees is now reduced due to work by the combined North Esk Landcare groups, who have removed thousands of tonnes of crack willows along the river floodplain which were blocking the river.

Today previous flows likely to cause flooding are contained within the banks and any flooding recedes within hours rather days resulting in less damage to properties and the riverbank.

Funding
A rescue effort of around $84,000, funded by the Australian Government Envirofund, has brought the choked river back to life.

Gus Green has volunteered for the North Esk River Landcare group for 15 years and said the results were "out of this world."

"Before we started you couldn't see the river at all, it was lifeless because of the willow infestations," Gus said.

Activities
"We had about 40 people working on it at one stage and we're still taking willows out. What started in 1989 with the formation of the landcare group has transformed an urban landcare situation into a project for the whole people."

The crack willows have since been used as mulch for newly-planted native trees, which revegetate a five kilometre stretch of riverbank.

On the other side of the river from Gus lives Dr Bill Wood, a marine scientist who in his spare time volunteers with the local Landcare group.

"Once the willows get old they fall over and block the flow. This increases drag and the river flows over its banks as the water can't get away," Bill said. "Farmers use the water for irrigation of high value crops, however even minor floods were inundating lucerne and poppy crops and threatening livestock. Once the willows were removed the problem improved out of sight."

Willows are European deciduous trees and when in leaf do not allow sunlight through water plants. This dramatically changes the ecology of the river.

"Now the river is returning to its natural state, you can regularly see platypus and spot the threatened Green-and-Gold-Frog. The valley is also supporting a diverse bird population including Sea Eagles and other raptors such as Peregrine Falcons."

Contrast the above with:

Snags return life to the Glenelg River, CASTERTON

Snags deposited in the Glenelg River near Casterton in south-west Victoria

More photos
Snags are being heaved back into the Glenelg River in southwest Victoria in a bid to recreate vital habitat for many native aquatic plants and animals.

In the 1960s and 70s logs and branches were removed from the 400-kilometre waterway, particularly in the reach flowing through the rural town of Casterton, off the Hamilton Highway near the South Australian border.

It was thought this would prevent flooding of the town by flushing out a build-up of sand in the river. Instead, the riverbed levelled out to what has been described as a 'flat highway of sand.'

Funding
In 2004 the Glenelg Hopkins Catchment Management Authority (CMA) initiated a project to restore in-stream habitat in the Glenelg River. The project received funding from the Australian and State Government-funded National Action Plan for Salinity and Water Quality and other contributions from the Victorian Government.

Activities
Glenelg Hopkins CMA's River Health Project Officer Lucy Cameron said over the past three years snags had been reinstated along a three-and-a-half kilometre stretch of river near Casterton.

"Large woody debris is an important natural component of most river systems," Lucy said.

"When tree trunks and limbs fall into the stream, they can slow the flow to create a deeper pool that supplies vital habitat for river plants and animals during drought. Debris also creates crevices and niches for invertebrates which in turn supply food for larger animals and fish."

Snags are sourced from a mineral sands mine operated by Iluka Resources at Douglas, about 20 kilometres from Balmoral. The company supplies the CMA with eucalypts such as Red Gum and Yellow Gum left over from its logging operations.

Woody debris is deposited near holes created where sand has been extracted. The combination of removing the sand build-up in the river, which was partially caused by a massive flood in 1946, and reinstating snags helps to create holes deep enough for species such as the Yarra Pygmy Perch to shelter from currents and predators.

Awareness-raising events have helped garner support from the local community, which has put its weight behind the re-snagging effort. Many residents of Casterton who remembered endorsing de-snagging now see the value of snags.

Achievements
"Seeing the scour pools created by those pieces of wood is very gratifying," Lucy said.

"Native fish that suffered as a result of habitat loss, such as River Blackfish, will be better off as they rely on these pools and hollow logs to lay their eggs."

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