Or are they? A recent study of a forest in Australia found that it was producing more CO2 than it was consuming.
Scientists suspected that a long drought in the region might be the reason for the trees and other organisms in the forest to release more CO2 than normal.
So far, the study is a single case
but it highlights the complexity of CO2 exchange between forests and the atmosphere and how sensitive the forest can be to changing temperature, rainfall and humidity.
In an attempt to understand
the situation in Thailand's forests,
a team of scientists recently erected a pilot 10-metre tower in the middle of Ratchaburi's deciduous forest to measure carbon flux - the net
difference between the CO2 gobbled up by photosynthesis and the CO2 produced by respiration.
Changes in the carbon flux rate help scientists monitor the increase of CO2 in the atmosphere. At the same time, it also helps them keep track of the health of the forest with changes in temperature, rainfall and humidity.
"Scientists all over the world are increasingly interested in carbon flux in forests," team leader Dr Amnat Chidthaisong, from the Joint Graduate School of Energy and Environment, said.
"Various types of forests in different part of the world exchange CO2 differently. Hopefully, our studies will contribute to the world's understanding of the role of forests as carbon sinks."
Amnat said the carbon flux measurement under his project is highly detailed. For every second, the equipment on the tower top will record carbon exchange up to ten times.
If the forest consumes more CO2 in the photosynthesis process than
it releases during respiration, it means it has high carbon storage capability.
If the rate changes, the data will allow scientists to analyse what is causing the variation.
"The records will help us keep pace with the increasingly volatility of the climate," Amnat said.
He said scientists from abroad have established similar carbon-flux-measuring stations in the other parts of Thailand, but it is hard for Thai scientists to get access to their data.
"I hope that this project will strengthen the expertise of Thai scientists and increase our knowledge of the impact of climate change on Thailand," Amnat said.