Rediscovered after 30 years, a forgotten Australian forest experiment challenged what scientists knew about logging and carbon storage
When researchers pushed through the overgrown access road to Tanjil Bren in 2014, they found a collapsed sign and a forest that had quietly swallowed any trace of the experiment it once marked. For nearly three decades, while Australians argued bitterly over clearfell logging, a silvicultural trial in Victoria’s Central Highlands had been running unmonitored and unfunded.
No one had been watching. But the trees hadn’t stopped growing.
A debate with no resolution — and an experiment no one remembered
Australia’s argument over clearfell logging has never been quiet. Since the 1970s, conservationists warned that cutting every tree in a block destroyed habitat for rare species. Foresters pushed back, arguing that mountain ash is naturally adapted to catastrophic fire and clearfelling simply mimics that process. Neither side convinced the other. The underlying questions — what clearfelling actually does, and whether less intensive alternatives could work — stayed unanswered.
In the mid-1980s, the Victorian government decided to find out. It invested the equivalent of A$26 million to launch the Silvicultural Systems Project at two sites: Tanjil Bren in Victoria’s Central Highlands, and Cabbage Tree Creek in East Gippsland.
The experiment was comprehensive. Researchers tested traditional wide clearfells, smaller patch clearfells, heavy thinnings removing 50–70% of trees, and left extensive unharvested control areas. Thousands of seedlings were monitored. The forest at Tanjil Bren was dense mountain ash regrowth from the catastrophic 1939 fires — old enough to be meaningful, young enough to still be changing.
By the early 2000s, initial results were in. Mountain ash regenerated best on clearfell sites. The findings were published. Then the access road grew over, the project sign collapsed, and the experiment faded from memory — the debate continuing as if the trial had never existed.
What the trees did when no one was watching
When University of Melbourne researchers returned to Tanjil Bren in 2014 — prompted by a colleague who had helped establish the original plots — they expected to document outcomes. What they found in the heavily thinned sections was, by their own account, astounding.
The trees left standing after thinning had grown enormous. At roughly 80 years old, the largest averaged well over a meter in diameter at chest height, and some exceeded 1.5 meters. The largest trees in the thinned stands were approximately 20% bigger in diameter than those in the unharvested control areas — forest that had never been touched.
The mechanism is straightforward, even if the scale wasn’t. Thinning removed competition, and surviving trees gained access to more light, water, and soil nutrients. Over three decades, they grew faster and larger than counterparts crowded into untouched stands.
Researchers had anticipated a degraded landscape — the visible aftermath of heavy harvesting. Instead, they walked into a vigorous, towering forest that had quietly outpaced the untouched controls in tree size.
The carbon surprise that challenged conventional wisdom
The size of the trees was striking. The carbon numbers were harder to absorb.
The heavily thinned stands had stored as much or more carbon in their wood than the unharvested control areas — despite having lost the majority of their trees during the initial harvest. In just 30 years, the thinned forest had recovered all the carbon removed during harvesting and accumulated enough additional carbon to match gains seen in untouched forest. That directly challenges a foundational assumption in forest policy: that logging inevitably reduces long-term carbon storage. Fewer, larger trees can accumulate carbon more efficiently than dense stands where trees suppress each other’s growth.
The thinned stands demonstrated that a carefully managed reduction in tree numbers can produce trees large enough to match carbon stored across an untouched canopy.
Wildlife wins in the thinned forest too
Large trees develop hollows — among the most critical and scarce resources in Australian forests. Species like the greater glider and Leadbeater’s possum depend on them for shelter. By producing trees of exceptional size, the thinned stands at Tanjil Bren may be accelerating the formation of exactly this habitat.
The acacia understory across thinned plots added another layer. Leadbeater’s possums use acacia for foraging and as movement corridors. Camera traps confirmed the result directly: Leadbeater’s possums were recorded in every thinned treatment plot surveyed, and in none of the unharvested control areas.
Bigger trees also offer greater fire resistance. In southeastern Australia, where bushfire frequency and intensity are increasing, a forest of large, robust trees is meaningfully more resilient than one of dense, smaller stems competing for the same resources.
What a forgotten experiment teaches forest management today
The researchers draw several lessons from Tanjil Bren. One is institutional: long-term silvicultural experiments are irreplaceable, and Australia’s forests contain many forgotten ones. Finding and protecting them before access roads grow over is urgent.
A second lesson challenges the debate itself. Thinning, applied appropriately, isn’t a trade-off between competing values. At Tanjil Bren, it delivered timber, matched carbon storage, and improved wildlife habitat simultaneously — an outcome that directly contradicts the conservation-versus-production framing dominating Australian forest policy for decades. Similar findings from North American conifer forests suggest the result may not be unique to mountain ash.
The third lesson is cautionary. There’s no silvicultural silver bullet. Thinning is a tool — potentially valuable in forests affected by clearfelling or high-severity fire — but it requires careful, context-specific judgment. No single technique transfers cleanly across every landscape.
What Tanjil Bren ultimately offers isn’t a prescription but a provocation. For 30 years, while the argument raged and the sign rotted, the trees demonstrated that the choices available to forest managers were broader than anyone in the debate admitted. The experiment didn’t resolve the argument. It reframed it.
Discover more information here: The Conversation. “A forgotten 30-year forest experiment just delivered a huge surprise.” ScienceDaily. ScienceDaily, 4 October 2026. <www.sciencedaily.com
Read the whole thing?
Get the week's signal, not the noise
Our sharpest reporting on energy, climate and nature — free, once a week.
