Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Thursday, 7 July 2011

Grassy White Box Woodland Restoration

Native grasslands and woodlands in Australia have been transformed since European settlement. Because they occur on the fertile soils (by Australian standards), and are dominated by palatable grasses, they were amongst the first ecosystems settled, and amongst the most intensively utilised. As a result, much of the original ecosystem has been lost - to cropping, to grazing, and to pasture improvement. Probably less than 15% of woodlands remain in eastern Australia, and grasslands occupy much less than 5% of their original range.

White Box woodland in a bush cemetery
(Photo: S. Prober)
But some remnants do survive - in areas that have escaped heavy utilisation such as bush cemeteries, travelling stock routes, town commons and railway lines. And they survive in relatively weed-free states with high native plant diversity. They provide a key insight into how degraded remnants might be restored.

Ian Lunt from Charles Sturt University and Suzanne Prober from CSIRO have been working for a long time now on the conservation and restoration of white box woodlands in southern Australia. Given the perilous state of these systems, their scientific studies are at the cutting edge of practical conservation biology.

They have looked at why small remnants have maintained their diversity - and come to the conclusion that soil nutrients plays a key role. Where nutrients are high, exotic plants are favoured and these tend to outcompete the small native species that have evolved to survive on scant resources. Where nutrients are low, native species thrive because the exotic species basically have too few resources to survive.

Soil nutrients increase for a couple of reasons - the most obvious one is that they are applied by farmers to increase productivity. Less well known, however, is that when deep-rooted, long-lived perennial native grasses such as Kangaroo Grass are lost from ecosystems, lots of nutrients (including nitrate) are released into the soil and the elevated levels favour annual grasses. Annual grasses, of course, are short-lived - so they use soil nitrate to grow and flower, but because they die each year, that nitrate gets released back into the soil to be used again in the following year by even more annuals. And so the cycle continues.

Therefore, the groundlayer of grazed and degraded remnants rarely recovers well after fencing and livestock exclusion because these sites often have high soil nitrate levels that favour the exotics. So, how to overcome this problem.

Ian and Suzanne have found that it is absolutely imperative that soil nutrients be reduced if native species are to be re-established, but this is easier said than done. Indeed, until their work begun, few conservation biologists had really thought about this problem in Australia. They have trialled a number of techniques in small experimental plots - well replicated of course! Their treatments included i) re-establishing deep-rooted perennial native grasses (to lock up nutrients), ii) burning (this leads to some loss of nitrogen in smoke), and iii) adding sugar (to reduce nitrogen availablility due to microbial activity).

The results have been nothing short of stunning, and give hope that grassy woodlands and grasslands can be restored. It's an example of how really good science can inform practical conservation outcomes. Their work has just featured on the ABC's science program Catalyst - which I've included here so you can see what this long-term study has been able to achieve.


No comments: