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Published: 8 August 2011

Willow seed-dispersal patterns key to control


A CSIRO project looking at the reproductive ecology and dispersal ability of the most aggressive invasive willow species in Australia is providing critical information to help land managers more efficiently control this weed.

CSIRO researchers have found that an average willow tree can produce as many as 330 000 seeds a year, which can travel more than 15 kilometres via wind or insects.
CSIRO researchers have found that an average willow tree can produce as many as 330 000 seeds a year, which can travel more than 15 kilometres via wind or insects.

Willows are a widespread weed in riverbank habitats across much of south-eastern Australia. They obstruct water flow, increase water temperature, change water chemistry and can displace native riverine plant species.

Willow control is expensive and time consuming. Eradication can be unsuccessful because of the willow’s capacity to reinfest areas soon after removal.

CSIRO researcher Ms Tara Hopley investigated the reproductive ecology and seed dispersal strategies of grey sallow (Salix cinerea), a Weed of National Significance (http://www.weeds.org.au/WoNS).

The study focused on three main problems: how willows are pollinated and how much seed they can produce; how far willow pollen and seed can move across catchments; and identifying which trees and populations within catchments are key seed ‘donators’.

‘We discovered that this species of willow is pollinated by both insects and wind, and that the average willow tree can make 330 000 seeds in a season,’ says Ms Hopley. ‘That is about 25 million seeds generated each year by an average infestation along half a kilometre.’

Ms Hopley used genetic paternity tests and spatial analysis to determine how pollen and seeds are dispersed across a typical catchment.

‘The results show that over half the pollen and seed is moving more than 15 kilometres between rivers. This high rate of spread suggests that land managers have to act urgently on control efforts across the whole catchment if long-term eradication is going to be effective,’ says Ms Hopley.

‘We also found a small proportion of sites studied were producing a large proportion of the seed. In practical terms, this means that clearing just 20 per cent of sites could see a 50 per cent reduction in seed production.’






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