Restoring Australian floodplains? Add water, reduce browsing, and lower salt*

In this post Associate Editor David Moreno Mateos discusses a paper he handled by Gillis Horner and colleagues ‘Recruitment of a keystone tree species must concurrently manage flooding and browsing’

It’s true, land management keeps getting complicated, especially when it gets to restoring sites. But the fact is that studies keep showing that we’re not that good at restoring ecosystems, essentially restored ecosystems tend not to get actually “restored”. Many reasons may explain that, and many solutions are needed to address this. Gillis Horner and the other authors of this paper made a great job of adding factors to the equation of restoring dry Australian floodplains. It was not only about restoring the hydrology of the heavily regulated streams of the Murray basin; it was also about herbivores, native and domestic, and also of salt. If the proportion of any of those ingredients failed, floodplains wouldn’t recover.

Two of the treatments the authors used in their study. Unflooded and browsed – the very worst one (left) and unflooded and unbrowsed (right). In any event, it seems that flooding does greatly help Red gum seedlings**. Credits: Gillis Horner and Rod John Horner.

Then you need to ensure an adequate flooding regime to allow seedlings to germinate, to prevent browsers eating at least some of the seedlings, and to prevent certain thresholds of salinity killing the sprouts. It actually doesn’t sound too complicated – it sounds more like you may need a bit of practice to get used to it. Given that flooding regimes similar to natural ones depend only on opening upstream dams at certain times, it is not a big deal if the water managers are not on the same page as you; it seems that a more important thing to do is controlling roaming herbivores at large scales. How would you do that if native predators (thylacine) are extinct and existing ones (dingoes) aren’t much loved by many? More research is needed to fix this***. Also, fencing floodplains along the huge basin might be quite challenging, although may be feasible. The option of de-extinguishing the Thylacine to control Australian herbivores may not be the best bet as of today, although it would be really cool. New studies are clearly needed to find the best ways to control browsers at that scale.

The other two treatments. Flooded and browsed (left) and flooded and unbrowsed (right). As the authors mention, either we have flooding and control large herbivores, or restoration is over. Credits: Rod John Horner and Charlie Coarser.

What would be really interesting is to see how things look after a while, since data reported from this study only span two years. How will the factors surveyed – flooding, herbivores, and salinity affect the assembly of Red gum forests after 10 or 20 years? Will they all be as important as they are at early stages over the long term? Will the effects of any of them fade over time? New limiting factors may also appear over time. That’s another story that will be worth telling.

UPDATES – 10.3.2016

*The title has been changed from ‘Restoring Australian floodplains? Try low salt & no browsing’

** Changed from ‘In any event, it seems that lack of flooding does greatly help Red gum seedlings.

*** Changed from ‘The authors propose reintroducing large predators, particularly, dingoes that could help control rabbits, kangaroos, and livestock. Although interesting, this may be a bit of an issue among dingo-hating ranchers all over Australia.’

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