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Stream Ecology

Weeping Willow

“I believe that the presence of willows along streams in agricultural zones can be shown to be almost universally preferable to cleared streams in those zones. I would also suggest that even relatively low-disturbance eucalypt-Acacia dominated riparian vegetation may not have compelling benefits over willows under many circumstances.” (Wilson, 2007)

It would be fair to presume the comment above had been made by Peter Andrews, Natural Sequence Farming originator and outspoken champion for the much maligned willow. In fact, this statement came from Dr Michael Wilson, a stream ecologist who supervised numerous PhD and Masters research projects in Ballarat, Victoria, during the early 2000s, comparing streams flanked by willows; 100 year old, multi-strata, native regrowth, and cleared land with introduced pasture.

The full paper which is linked to at the bottom of this article goes into more detail, but here’s a summary from Wilson (2007) to give you the gist:

– On average, willow-lined streams had a higher retention of sediment (187t more/km) and organic matter (30t more/km) than the native forest.

– “Willow-mediated aggradation in these channels is converting them from incised channels to in-fill channels that are more characteristic of pre-European conditions”.

Litterfall of willow and native-reveg reaches had a similar annual distribution pattern due to the not-so-well-known summer dominant leaf drop habit of many Eucalypts.

– The annual weight of leaves, twigs, bark and flowers was very similar at the willow and native sites.

– With similar annual litterfall amount and distribution, coupled with dense shade patterns in the seasons of maximum productivity, the overall metabolism (and resulting biological oxygen demand) was also very similar.

– Root mats of willows were found to provide beneficial habitat to native fish in the absence of large woody debris.

– There was a disproportionately large association between pool-riffle sequences and willows, formed by the root mats of the willows.

“Pool-riffle sequences are extremely valuable habitat and for that reason alone it is worthwhile (maintaining willows). But it becomes even more valuable when it can contribute to ideas focused on restoring the whole of the floodplain complex in agricultural landscapes.”

“In all the streams we have studied, clearing willows will mobilise sediment, nutrients and organic matter, will make heterotrophic streams more autotrophic, will threaten habitat values for invertebrates and fish and will threaten pool-riffle sequences. Native vegetation planted where willows are cleared will take many decades if not hundreds of years to mature, for the canopy to close over and for significant limb fall to occur.”

View the full article:

Click here to view the full article, Willows: Weeds of Retention 

Wilson, M., 2007. Willows: Weeds of Retention. Proceedings of the 1st Natural Sequence Farming Workshop. ‘Natural Sequence Farming: Defining the Science and the Practice’, Hazell, Peter and Norris, Duane, Bungendore, NSW,  2007. http://www.nsfarming.com/workshop/

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