Virtual Museum of Canada
Jardin botanique de Montréal 
Centre for Forest Research

Nutrients in the forest

Carbon fixation

Why do people say that forests are carbon sinks? Easy. Like other plants, trees capture carbon dioxide (CO2) from the air and use the carbon in it to synthesize the organic material they need to build their tissues. The carbon is no longer in gaseous form, but now in solid organic form in the trees' wood. This means that forests play a crucial role in the carbon cycle – a role we need to understand more clearly, in the context of climate change.

Breathe in... breathe out...

Every cell in the tree, just like those in our own bodies, "burns" organic compounds to get the energy it needs to function. This is called cellular respiration. The end product of the process is carbon dioxide, unusable waste that trees and animals release into the atmosphere. To evaluate the amount of carbon dioxide released by trees as a result of cellular respiration, in comparison with the amount of carbon dioxide fixed through photosynthesis, scientists use a carbon balance. When it is positive, the tree is absorbing more than it is releasing; when it is negative, the opposite is true.

Videoclip Transcription