A landmark study of the towering ash trees that grow in the mountains of Victoria, Australia, which was launched in the 1980s, boosted arguments for clearcutting the iconic trees. But when scientists returned to the site years later, they came to a much different conclusion.
Australian conservationists have long contended that clearcutting imperiled koalas and other native wildlife. Foresters, on the other hand, argued that mountain ash trees, which can grow taller than 300 feet and live for more than 400 years, were adapted to catastrophic bushfires that cleared the forest, leaving nothing behind. They pointed to stands of ash trees that were essentially uniform in age — evidence that the forest had been leveled and then regrew — and said that by clearcutting ash and burning any detritus that remained, they were recreating the effects of the most intense fires.
To settle the argument between conservationists and foresters, scientists launched a landmark experiment in Victoria's Central Highlands in 1987. They compared large clearcuts, which could be more than 1,000 feet wide; small clearcuts, some less than 200 feet across; and plots that had been heavily thinned, with at least half of trees removed.
By the early 2000s, it was clear that mountain ash regrew best in the footprints of large clearcuts, giving credence to the foresters' argument. In the smaller clearcuts and thinned plots, the study found, shorter acacia trees dominated. The results were published and the experiment abandoned.
However, when scientists returned to the site in 2014, they noticed something surprising: While mountain ash were abundant in the clearcuts, both large and small, in the thinned plots, ash trees had grown at a startling pace.
Monitoring showed that, with few competitors, the biggest trees in the thinned plots were 20 percent larger in diameter than trees in areas that had never been harvested. They also stored at least as much carbon, meaning that, in just a few decades, the surviving ash in the thinned plots had recovered all the carbon lost to logging, and then some. The findings were recently published in Forest Science.
The study authors say that bigger trees are more resistant to fire and more likely to form the hollows where greater gliders and Leadbeater's possums make their homes. Thinning, they say, offers a way to supply timber while also preserving vital woodlands and their stores of carbon.
"Our findings show this for mountain ash, and other studies in North America have shown this for conifer forests," they said, writing in The Conversation. "It is a win-win-win outcome that challenges the false dichotomy of conservation versus production that has dominated public debate for decades."
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