Australia’s temperate grazing region is facing a tree regeneration crisis, with new research from The Australian National University suggesting that millions of hectares could be treeless within decades.
A research project based at the Fenner School of Environment and Society at ANU has found that the majority of scattered paddock trees in grazing areas are old and close to death, yet there are virtually no young trees growing to replace them. The results are published in the latest edition of the US-based Proceedings of the National Academy of Sciences (PNAS).
“We studied a one-million-hectare area in the Upper Lachlan catchment in NSW, but our findings are applicable for much of the temperate grazing region, especially in New South Wales and Victoria,” said team leader Dr Joern Fischer from ANU.
“Tree cover is sparse over much of the region and many trees are very old, especially where past clearing has been extensive. Typical paddock trees are often over 140 years in age and, in many locations, no young trees have regenerated for decades.
“This age profile of trees, with many old trees and virtually no young trees, is not natural. By way of contrast, we found that in long-ungrazed locations young trees were the most common age group. Our findings have serious implications – under existing management practices, millions of hectares of land currently supporting tens of millions of trees will be treeless within decades from now.”
The researchers argue that the disappearance of paddock trees would have many negative effects for agriculture and natural ecosystems, removing shelter for livestock, habitat for birds and other wildlife, decreasing water infiltration, and risking detrimental flow-on effects for the entire ecosystem.
“But the good news is that management practices exist that can reverse the tree regeneration crisis,” Dr Fischer said. “We found that trees are more likely to regenerate in unfertilised pastures where soil nutrient levels are low. We also found that trees are more likely to regenerate under high-intensity rotational grazing than under conventional, continuous grazing.”
Dr Fischer and his colleagues have developed a short list of tangible management options for maintaining paddock trees that could assist farmers and other land managers.
“Ultimately, maintaining tree cover over vast areas cannot be done without nature’s help,” Dr Fischer said. “Hence, farm ecosystems must become self-sustaining, allowing for natural tree regeneration while also providing an income to farmers.”
The research was funded by the Australian Research Council and the Commonwealth Environment Research Facilities program.
