Why should you not sleep under a tree at night?

During the night, plants do not produce oxygen. This is because photosynthesis requires sunlight, and without sunlight, photosynthesis cannot occur.

However, plants still need energy to carry out their life processes. Just like animals, they undergo respiration, in which glucose is broken down to release energy.

Glucose → Energy + Water Vapour + Carbon Dioxide

As a result, plants consume oxygen and release carbon dioxide during the night.

This is why it is generally advised not to sleep directly under a tree at night. In the absence of photosynthesis, the tree continues to respire, releasing carbon dioxide into the surrounding air.

Note: While a single tree in an open, well-ventilated area is unlikely to pose a serious risk, the principle serves as a useful reminder of the difference between photosynthesis and respiration, and how plants behave differently during the day and at night.