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Victoria's charred forests awash with green


Eucalypt seedlings form a green carpet for the blackened ballroom.  [Image: Bruce Hungate]


Towering stags form a bleak overstorey [Image: Bruce Hungate]


Tree climbers must take wood samples now, before the trees become unsafe to climb.  [Image: Bruce Hungate]

Prof George Koch
Professor of Biological Sciences
Northern Arizona University
Flagstaff, AZ 86011, U.S.A.

"Although it has escaped fire for nearly a century, this seems to have been pure chance."

David Ashton (2001)1 writing of the Wallaby Creek area and its stands of 300 year old Eucalyptus regnans.

Until the Black Saturday fires of February 2009, the Wallaby Creek watershed on the Hume Plateau, Victoria, was home to one of the most magnificent stands of Eucalyptus regnans in Australia.  The oldest and largest trees germinated in 1701 and had reached 92 meters in height. Having worked at Wallaby Creek since 2005 on studies examining the relationship of tree size to growth rate2, we were keen to see first hand how our study trees and the forest had fared in the wake of the fire.  With support from the U.S. National Science Foundation and logistical help from Parks Victoria, we spent 10 days in late March studying the fire’s impact on carbon stocks and assessing regeneration.   We also took the opportunity to collect wood samples from the giant trees for anatomical studies before decay made the trees unsafe to climb. Members of our team included Drs. Bruce Hungate, Matthew Hurteau, and George Koch, graduate student Cameron Williams, Mr. Giacomo Renzullo of EcoAscension Environmental Consulting, and professional arborists Tom Greenwood and Joe Harris of The Treeworks in Melbourne.

The visual impression of the forest was stunning: nearly every tree was dead, yet its skeleton was complete, with even the finest branches intact.  Flames apparently did not reach the crowns of the tallest trees, which dropped their parched leaves in the months following the fire. A few Big Ash, seemingly less than 1 in 1000, survived in isolated patches scattered about the forest. At slightly lower elevations and around the margins of the area dominated by E. regnans, messmate (Eucalyptus obliqua) that were burned in the fire had “fuzzed out” with copious new bright green epicormic shoots along their main stems.

The woody understory of hazel (Pomaderris aspera), daisy bush (Olearia argophylla), and silver wattle  (Acacia dealbata) was destroyed, while tree ferns (Cyathea australis) weathered the fire well and have produced vigorous new fronds. The forest floor was thick with seedlings of the woody species as well as kangaroo tomato (Solanum aviculare), wire grass (Tetrarrhena juncea), and saw grass (Gahnia sieberiana). Ash seedling densities were 25 to 30 per square metre, considerably down from the >100 per square metre measured by Tom Greenwood and big tree expert Brett Mifsud a couple of months after the fire.  The young ash trees were already one to two meters tall and winning the race toward the sky. Most will succumb to competitive pressure or be crushed by falling trunks and branches of their progenitors. A few, however, will probably survive and exhibit the prodigious growth rates for which E. regnans is famous.

It will be fascinating to watch the post-fire succession of the Wallaby Creek area over the coming decades. Will the Big Ash emerge again as the overstorey dominant, or might climate change prevent the re-establishment of one of the world’s great forest ecosystems?

1Ashton, D. H. 2000. The Big Ash forest, Wallaby Creek, Victoria - changes during one lifetime. Australian Journal of Botany, 48:1-26.
2Sillett, S. C., R. Van Pelt, G. W. Koch, A. R. Ambrose, A. L. Carroll, M. E. Antoine, B. M. Misfud. 2010. Increasing wood production through old age in tall trees. Forest Ecology and Management. 259: 976-994.

Biobuzz issue eleven, May 2010