ScienceWise - Sep/Oct 2009

Dead Wood

Article Illustration
Dr Joern Fischer
Article Illustration
Trees have ecological, economic and cultural value. They provide habitat for wildlife and shade for livestock, they assist with water infiltration into the soil, and they are iconic parts of the Australian landscape. Given the importance of maintaining tree cover, what can we do to reverse the crisis in tree regeneration that threatens to transform our landscapes in the coming years?

Reversing a Tree Regeneration Crisis

It’s long been known that paddock trees in much of Australia’s temperate grazing region are not regenerating. With every year we lose a few more as the old trees die but nothing is coming through to replace them. In recent years there’s been a growing realisation that the situation is rapidly evolving into a crisis.


“Under existing management practices, millions of hectares of grazing country, currently supporting tens of millions of trees, will be treeless within decades from now,” says Dr Joern Fischer from the Fenner School of the Environment and Society. “And the loss of this tree cover is predicted to lead to massive declines in biodiversity and grazing productivity.”


Dr Fischer’s Sustainable Farms research group has spent the last couple of years documenting the extent of the tree regeneration failure and has been investigating if the situation can be reversed by changing land management.
“Although clearing has largely stopped, tree cover continues to decline because many existing trees are dying of old age, and few young trees are regenerating,” says Fischer. “We studied a 1,000,000 hectare area in the Upper Lachlan catchment of New South Wales. Typical paddock trees are often over 140 years old, and in many locations, no young trees have regenerated for decades.”


But it’s not all bad news. The researchers also found that trees do regenerate under some management practices. For example, it was found that trees are more likely to regenerate in areas with low soil fertility or under high-intensity rotational grazing (as opposed to conventional continuous grazing).


“Our study identified a short list of management options for maintaining paddock trees,” says Fischer. “In some areas, natural regeneration is unlikely in the short term, for example because there are few parent trees, or because soil nutrient levels are high. In such areas, scattered trees can be planted with re-usable tree guards that protect individual trees from livestock – some pioneering farmers are doing this already. Another option is to temporarily exclude livestock from a paddock prior to re-seeding it and resting it for several years – an approach successfully used by Greening Australia in the Canberra region.”


Ultimately, however, the study found that maintaining tree cover over vast areas cannot be done without Nature’s help – that is to say via natural regeneration. Therefore, farm ecosystems must become self-sustaining, allowing for natural tree regeneration while also providing an income to farmers.


“Our findings suggest that self-perpetuating farm ecosystems with farms trees can be created by applying high intensity rotational grazing with long rest periods, and by phasing out fertiliser use,” explains Fischer. “Even where these practices are adopted, changes in tree regeneration will not occur overnight. But unless significant changes in management are introduced now, old trees will continue to disappear, and opportunities for natural regeneration will continue to be lost.
“The future of Australia’s paddock trees depends on urgent and widespread management action. While mature trees still exist, they provide regeneration nuclei throughout the landscape, thereby offering a window of opportunity to reverse the tree regeneration crisis.”


More Info: http://www.pnas.org/content/106/25/10386.abstract

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