Image Courtesy: Centre for Forest Tree Technology
A decades-old forest experiment in Victoria, Australia, has revealed that selectively thinning trees could help forests store substantial amounts of carbon while supporting wildlife and timber production. The findings challenge the long-standing assumption that forests must be left untouched to maximize their ecological value.
The research focused on mountain ash forests at Tanjil Bren in Victoria’s Central Highlands, where scientists established experimental plots between 1987 and 1989 to compare different forestry methods. The project examined traditional clear-cutting, smaller clear-cut patches, heavy thinning, and untouched forest areas. Researchers revisited the site in 2014 and discovered that the effects of the different approaches remained visible decades later.
The original experiment found that mountain ash regenerated most successfully in large clear-cut areas. However, the long-term results revealed another unexpected outcome. Trees left standing in heavily thinned plots had grown remarkably large, with the biggest specimens averaging more than one meter in diameter at chest height. Some exceeded 1.5 meters.
These trees were approximately 80 years old, and their diameters were around 20% greater than those of trees in unharvested control areas. With less competition for sunlight, water, and nutrients, the remaining trees had more resources available for growth.
The researchers also found that heavily thinned forests stored as much or more carbon in their wood as untouched comparison areas. Within 30 years, these stands had recovered the carbon removed during harvesting and accumulated additional carbon comparable to the gains recorded in unharvested forests.
The findings could also have important implications for wildlife. Larger trees are generally more likely to survive fires and develop hollows that provide shelter for threatened species, including the greater glider and Leadbeater’s possum. Meanwhile, acacia vegetation growing across several experimental treatments provides food and movement corridors for Leadbeater’s possums. Camera traps detected the animals in every harvested treatment surveyed, but not in the unharvested areas.
The researchers emphasize that thinning is not suitable for every forest, particularly those requiring strict protection. However, the results suggest it could offer an alternative to intensive clear-cutting in some landscapes.
The experiment also highlights the value of preserving long-term scientific research, which can reveal ecological changes that shorter studies miss.
