The scientists from the University of São Paulo in Brazil have completed a 30-year research in the eastern Amazon which revealed that the logging method directly affects the rate of forest carbon stocks recovery. Conventional selective logging requires about 32 years for a forest carbon offset, while the use of the low-impact logging techniques reduces it to 9 years.
The Amazonian forests play a crucial role in the global carbon cycle. According to the researchers’ estimates, these forests absorb roughly 20% of CO₂ the planet terrestrial ecosystems absorb annually. Trees capture carbon dioxide from the atmosphere and store it in their wood for decades. However, deforestation disrupts this process: some of the stored carbon is released back into the atmosphere, and the forest ability to absorb new emissions decreases. So, to assess the climate impacts of forest use, it is important to understand not only the scale of deforestation but also a forest’s recovery time.
To do this, Brazilian scientists monitored three sections of the Amazon rainforest, covering a total area of 73.5 hectares, for over three decades. One forest section remained untouched, the second underwent a conventional selective logging, and the third one utilized a low-impact logging technology which is a gentle logging method when the machinery routes and tree felling direction are planned in advance to minimize the damage to the surrounding forest. This comparison allowed for a direct assessment of the impact different logging methods make on ecosystem recovery.
The researchers tracked the fate of thousands of trees and assessed separately the contribution of the three processes in forest recovery: growth of surviving trees, emergence of young trees, and tree mortality. It is the ratio of these processes that determines how quickly a forest recovers its lost carbon stocks.
It turned out that low-impact logging not only accelerates forest recovery but also alters its long-term dynamics. The average net increase was about 1.67 tons of carbon per hectare per year. In the early years after the logging, tree mortality here was about 14% lower, and the young trees contribution to forest regeneration was 26% higher than with conventional logging. As a result, the forest offset carbon losses related to timber harvesting much faster.
The benefits of this approach have been sustained in the long run. Even 30 years after harvesting, the forests where the low-impact methods were used continued to sequester carbon significantly faster than the areas that had undergone conventional clear-cutting. An additional increase amounted to about 0.46 tons of carbon per hectare per year, compared to 0.18 tons with the conventional approach. This shows that the consequences of choosing the logging technology have been felt for over several decades.
The key role here belongs to large trees. They contain the bulk of the carbon stored by the forest, and low-impact logging allows for preservation of a lot more such trees after harvesting. At the same time, more favorable conditions are created for natural forest regeneration. The damage done by conventional logging is significantly greater, more trees are lost, and the resulting carbon deficit persists for decades.
According to the researchers, over 30 years, one hectare of forest harvested with the low-impact methods can sequester additional 192 tons of CO₂, which is twice as much as after conventional logging. Application of such methods to tens of millions of hectares of the Amazonian public forests might have an additional effect amounting to billions of tons of CO₂. The researchers estimate that just switching from traditional logging to low-impact logging would result in additional absorption of about 6 billion tons of CO₂, which is comparable to nearly eight times the annual emissions of the entire Amazon region.
