The main reason the concentration of carbon dioxide in the air in a forest is high is due to the increase in plant growth.
Explanation:
Plants release carbon dioxide because of the process of respiration in which plants take in oxygen and give out carbon dioxide. During the day, carbon dioxide enters through the tree's pores, making oxygen escape (and is consistent with the “reverse lungs” concept).
On the other hand, at night, oxygen enters through the pores, and carbon dioxide escapes, rather than oxygen.
