Where there’s a willow there’s a way

Willow trees, in particular Salix cinera, the grey sallow or “wild pussy willow“, are serious problem weeds in southeastern Australia. They infest riverbanks, harming both indigenous flora and fauna: they drive out native plants and clog waterways for fish and other freshwater animals.

Riverbanks infested by willows (click to embiggen)
Grey sallow willows were introduced into Australia more than 70 years ago, but now they're weeds that infest 2000 km of riverbanks (Image copyright CSIRO)

Because you have to know your enemy if you want to defeat them (thank you, Sun Tzu), CSIRO scientists Tara Hopley and Andrew Young have been researching grey sallows at sites in Victoria’a Ovens River catchment to find out how they reproduce and spread their seeds.

They found that a single tree can produce 330,000 seeds in a single season. They are pollinated by both wind and insects, and genetic paternity tests have shown they can spread their seed over 15 km.

This makes them very effective propagators, and so if you want to control them you need to work over a wide area with the cooperation of different landowners.

But on the plus side, the seeds were also found to be short-lived: they do not germinate 8 weeks after release. Also, a lot of the seed came from only a small number of sites: they calculated that it’d be possible to cut seed production by 50% from clearing only 20% of sites.

To read more about this effort to understand pests in order to beat them, see the CSIRO fact sheet – War on willows (PDF 2 MB).

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2 thoughts on “Where there’s a willow there’s a way

  1. G’day,

    You guys are promoting a seriously unenlightened view of these wonderful plants. Why the obsession to control nature? Perhaps try working with her instead, she’s been around a lot longer than us mere mortals. Try this link for starters by the great Australian thinker (among other things) David Holmgren.

    http://www.thecourier.com.au/news/local/news/business/willow-tree-removal-contributed-to-floods-environmentalist/2094584.aspx

    Apart from stitching the banks together, willows provide livestock fodder, pollen and nectar for bees at a time when few plants are flowering, habitat, timber and basketry materials, a traditional cure for rheumetic complaints and a modern pain relief in acetylsalicylic acid – aspirin (though synthesised now I believe).

    I am familiar with the area through which the Ovens River runs and I remember what it was like before the willows were removed from sections of the banks of the Kiewa River. The banks were washed away soon after and the ecology with it. You can still go to parts where the willows grow and they are full of life, biodiversity and beauty. Put your faith in nature friends. Just because it doesn’t always necessarily fit in with our modern modes of thought doesn’t mean that it isn’t working in a positive way – we just need to better understand it. Ecology is constantly evolving.

    Cheerio,

    Dan Park

    1. Hey Dan,
      I understand your point, if there’s nothing to replace them, the Willows in Australia are preventing erosion, amongst other things, but they are reducing biodiversity overall by reducing the numbers of native species in the same areas. Before the Willows were there, native trees stood in their place, and nourished native insects and other animals like fish that feed on them. The spawning habits of local fish are also not suited to the shallow water that willows create in waterways, while European fish like Carp are more suited. Ultimately, I agree, in some cases they may be doing a good job, but they are not really enhancing biodiversity by displacing local species, just making Australia more like Europe.

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