Forests that are recovering from logging can act as a source of carbon sequestration. This means that the trees in the forest are absorbing carbon dioxide from the atmosphere and storing it in their biomass, which helps to mitigate the effects of climate change. However, the rate of carbon sequestration can vary depending on the specific conditions of the forest and the type of tree species present. Additionally, it’s important to note that while forests can be an important source of carbon sequestration, they can also be a source of emissions if they are burned or cleared, releasing the stored carbon back into the atmosphere.
A new study finds that tropical forests recovering from logging are carbon sources for years afterward, contrary to previous assumptions. Because new trees grow quickly, tropical forests that have recovered from tree removal were thought to be carbon absorbers. The carbon released by soil and rotting wood outpaces the carbon absorbed by new growth, according to a new study led by Imperial College London researchers.
According to the researchers, the findings highlight the need for logging practices that minimize collateral damage in order to improve the industry’s sustainability. The study, which tracked carbon in Malaysian Borneo forests as part of the Stability of Altered Forest Ecosystem (SAFE) Project, was published today in the Proceedings of the National Academy of Sciences.
A large portion of the carbon released in recovering forests comes from collateral damage, which includes trees that died as a result of logging damage and were left to rot, as well as disturbed soil. Logged forests still have value because we know they have unique biodiversity, so ensuring that they are not releasing extra carbon through better logging practices will increase their sustainability.
Dr. Terhi Riutta
First author Maria Mills, who began the work at Imperial and completed it at the University of Leicester, said: “Our results show that for the tropical forest we studied, logged areas are a source of carbon even a decade after logging has occurred. This means we need to reassess their role in global carbon budgets — we can no longer apply the blanket assumption that they are carbon sinks.”
Dr. Terhi Riutta, lead researcher and now at the University of Exeter, stated: “A large portion of the carbon released in recovering forests comes from collateral damage, which includes trees that died as a result of logging damage and were left to rot, as well as disturbed soil. Logged forests still have value because we know they have unique biodiversity, so ensuring that they are not releasing extra carbon through better logging practices will increase their sustainability.”
Many previous studies of recovering forests have focused on measuring tree growth to estimate the amount of carbon taken from the atmosphere. The new study also measured how much carbon was coming from the ground (soil and dead wood) to calculate the carbon budget from the incoming and outgoing carbon flows for logged and unlogged (old-growth) forest.
The logged forest plots in the study had been logged at various stages over the previous few decades. Between 2011 and 2017, the measurements were taken. Researchers used a portable carbon dioxide monitor to test patches of ground and deadwood in several plots monthly for several years to measure the carbon released from the ground. The team had also erected a 52-meter-tall tower above the forest canopy to continuously measure the ‘flux’ of carbon into and out of the forest in order to determine whether it was a net source or sink of carbon.
They found that unlogged forested areas are generally carbon neutral, but that moderately and heavily logged tropical forest areas are a carbon source. They estimate an average carbon source of 1.75 +/- 0.94 tonnes of carbon per hectare within moderately logged plots and 5.23 +/- 1.23 tonnes of carbon per hectare in severely degraded plots, with emissions continuing at these rates for at least one decade after logging.
Professor Rob Ewers of Imperial’s Department of Life Sciences, a co-author, stated: “The tower measurements reveal whether the forest area is a carbon source or sink, and soil monitoring explains why. We know from these measurements that logged forests continue to be a source of carbon for up to a decade after they have been logged, and that this is primarily due to organic matter in the soil or rotting wood.”
Carbon monitoring should be carried out in other forests in different regions, according to the team, in order to build a more accurate picture of how logged forests contribute to global carbon budgets.
