Scientists forgot about an experiment in the forest. They returned 40 years later - and were amazed

In the late 1980s, an ambitious experiment was launched in Australia to answer a seemingly simple question: what is the best way to log trees without destroying the forest in the long term? Researchers marked areas, logged trees using different methods, and began tracking what grew in their place. For years, data was collected - and then the project gradually faded, access roads became overgrown with vegetation, and the sign marking the experiment site fell to the forest floor.

The trees, of course, did not know that the research had been almost forgotten. They simply continued to grow.

Decades after the start of the experiment, researchers from the University of Melbourne returned to the forest in Tanjil Bren in the state of Victoria. What they found there provided a rare glimpse into what happens to a forest over a very long period after human intervention - and the most surprising result appeared precisely in the areas where a large portion of the trees were logged, but not all of them.

The experiment intended to find an alternative to clear-cutting an entire forest

In the 1980s, a fierce debate took place in Australia surrounding clear-cutting - a method in which all mature trees, or almost all of them, are logged in a certain area at once.

From the perspective of the timber industry, the method was efficient and also allowed certain species to regenerate well. On the other hand, environmental organizations warned that when an entire area is logged, animals and plants can lose their habitat all at once.

To test if there is another way, the government of Victoria invested a large sum in a long-term research program. Between 1987 and 1989, experimental sites were established in Tanjil Bren in central Victoria and in Cabbage Tree Creek in the east of the state.

Researchers divided the forest into areas and treated each one differently. In some areas, clear-cutting was performed, in others, smaller clearings were opened, and in some, heavy thinning was performed - meaning 50% to 70% of the trees were logged and the rest were left standing. Alongside all these, forest areas that were not touched at all were also preserved to serve as a comparison group.

Thousands of saplings and trees were measured over the years. At first, it seemed that the answer was quite clear. By the beginning of the 2000s, it was found that eucalyptus trees regenerated particularly well in areas that were completely logged. In areas where large trees remained or only small clearings were opened, regeneration was less strong.

The results were published, monitoring gradually decreased - and the experiment was left behind.

And then the researchers returned to the forest

In 2014, a group from the University of Melbourne arrived in Tanjil Bren as part of their forestry studies. One of their colleagues, who was involved in setting up the original experiment, suggested they visit the area and see with their own eyes what happened to each of the treatment methods.

Almost 30 years after the original logging, some of the old results were still clear. In the areas that were completely logged and in the large clearings, many vigorous eucalyptus trees had grown.

But then they reached the areas that had undergone heavy thinning.

The trees that remained there were enormous.

Although they were only about 80 years old, the diameter of the largest ones was on average more than a meter at chest height, and some trees reached a diameter of more than a meter and a half. The researchers explained that the reason is quite logical: after most of their neighbors were logged, the remaining trees received much more space, light, and resources - and utilized them well.

The largest trees in the thinned areas were about 20% wider than the largest trees in the forest areas that were not logged at all.

But the size was only the beginning.

They regained all the carbon lost in the logging

When the researchers examined how much carbon was stored in the wood over the years, they discovered an even more surprising result.

The areas that underwent heavy thinning stored an amount of carbon in their wood similar to - and in some cases even higher than - that found in the forest areas that were not logged.

Within about 30 years, the accelerated growth of the remaining trees actually managed to compensate for the carbon lost when the rest of the trees were logged. Moreover, the thinned forest has since accumulated additional carbon at a rate that equaled the increase recorded in the control areas that did not undergo logging.

From the researchers' perspective, this is a significant result because it challenges the assumption that the choice must always be between producing wood and maintaining the forest's ability to store carbon.

Large trees also have other advantages. They are more resistant to fires than small trees, so their chance of surviving a fire is higher. As they grow and mature, the chance that natural cavities will form in them, which serve as a home for animals, also increases.

One of them is the Leadbeater's possum, a rare small marsupial that lives in these forests and needs a combination of trees with cavities and dense vegetation to find shelter, move, and obtain food.

When the researchers placed surveillance cameras in the experiment areas, they found the possums precisely in the areas that underwent heavy thinning - and not in the control areas that were not logged. The researchers emphasize that this is only one species out of an entire ecosystem, so it is impossible to conclude from this that thinning is always the right solution.

So should we start thinning forests? Definitely not everywhere

Despite the impressive result, the researchers warn against turning it into a universal recipe.

The findings do not mean that thinning trees is always the best choice, and certainly not that every forest should undergo partial logging. The type of forest, the age of the trees, the animals living in it, the risk of fires, and the goals of land management can completely change the result.

Clear-cutting also did not "fail" in the experiment. On the contrary - in the areas that were completely logged, a new, dense generation of eucalyptus trees grew, exactly as the first studies showed. Different methods simply created, over decades, very different forests.

And this, from the researchers' perspective, is one of the most important conclusions: there is no single method capable of solving all problems.

Thinning may in some cases allow for wood production while simultaneously maintaining carbon stocks and encouraging the formation of large trees and a more complex forest structure. In other places, leaving the forest without intervention or using a different method may be more correct.

The new research also offers a broader lesson that is not just related to trees: sometimes experiments that seem to have ended have only just begun to provide the truly interesting answers.

Across Australia, there are other old forestry experiments that have been neglected over the years due to budget cuts, policy changes, or changes in government bodies. The researchers believe it is worth finding them and checking what happened in them.

After all, one can stop funding research, disband a team, and let the road leading to it disappear into the vegetation. The forest itself has a completely different schedule.