Researchers in Victoria, Australia have revisited a major forestry experiment established between 1987 and 1989 to compare different approaches to forest management. The Silvicultural Systems Project, launched with government investment equivalent to A$26 million, studied mountain ash forests at two locations: Tanjil Bren in the Central Highlands and Cabbage Tree Creek in East Gippsland. The original experiment examined how forests regenerated under various management practices, including traditional clearfelling, small patch clearfells, and heavy thinning operations where 50-70% of trees were removed.
Early findings published in the early 2000s indicated that mountain ash regenerated most successfully in clearfelled areas, while retaining tall canopy trees or using small clearfell patches resulted in dominance by understory species like acacia. The project was subsequently abandoned and largely forgotten as the access road deteriorated and site markers disappeared. However, when researchers returned to the Tanjil Bren site in 2014 as part of a university forestry program, they discovered unexpected long-term outcomes from 30 years of forest development.
The heavily thinned forest sections displayed the most remarkable results. Trees that had been left standing after thinning operations had grown to enormous sizes, with many exceeding one meter in diameter at chest height and some surpassing 1.5 meters. These trees were 20% larger in diameter than those in unharvested control areas. Most significantly, the thinned stands had accumulated carbon equal to or greater than the unharvested control areas, meaning the forest had fully recovered the carbon removed during harvesting while matching the carbon gains of protected forest.
The research revealed additional benefits beyond carbon recovery. Larger trees demonstrate greater fire resistance, improving survival prospects during future fire events. The bigger trees are also more likely to develop hollows that serve as critical habitat for endangered species such as the greater glider and Leadbeater’s possum. Camera trap surveys confirmed that Leadbeater’s possums appeared in all silvicultural treatment plots but were absent from unharvested areas, suggesting thinned forests provided better foraging and movement corridors through acacia growth.
The findings challenge the traditional dichotomy between forest conservation and timber production. Researchers conclude that strategic thinning represents a potential “win-win-win” approach by simultaneously delivering wood for industry, maintaining carbon stocks, and enhancing wildlife habitat. The study also highlights the value of long-term forest experiments and calls for identifying and protecting similar forgotten research sites that could provide crucial insights into forest management practices for Australia’s future forestry policy debates.
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