Thanks to our seventh grade science teachers, we know that trees do breathe. Just like any other living organism, trees take in nutrients, water, and sunlight to produce energy and grow. And similarly to humans, trees can breathe — but unlike humans, it’s not oxygen they're pulling in.

Trees pull in carbon dioxide before releasing oxygen. Because trees don’t have lungs, this isn’t a process that can be seen. It happens at a cellular level, invisible to the human eye, but that doesn’t make it any less important. In fact, most plants breathe this way. It’s one of the critical ways they produce atmospheric oxygen and clean the air surrounding us. 

The next time you take a deep breath, make sure you thank a tree!

During the spring and summertime, the leaves of a tree pull in carbon dioxide, water, and energy from the sun to turn into sugars that produce nutrients. This process, which is called photosynthesis, then emits oxygen that helps other living things breathe.

Typically, this process is most active during spring and summer –– when trees aboveground parts are growing more vigorously. During the fall, trees begin preparing for winter, dropping their leaves (if they are deciduous), and going into dormancy. When chlorophyll production dwindles, leaves begin losing their vibrant green color and photosynthesis begins to slow down.

The breaking down of chlorophyll makes it harder for trees to absorb sunlight and use it to produce energy. Because of that, leaves slowly begin to lose their green color, transforming into different hues of red, brown, and orange.

Once winter begins, trees reach a state of dormancy. Similar to hibernation, dormancy simply means that trees are conserving their energy for the bracing season ahead. During this time, trees don’t actively photosynthesize or produce oxygen, causing oxygen levels to fall and carbon dioxide to rise. 

Trees more than make up for the lowered oxygen levels in the spring and summertime, so humans tend not to be too affected when trees go dormant.

Now that we know how trees breathe, it’s important to understand just how much oxygen a tree produces. While most oxygen is produced by phytoplankton, trees still play a significant role in providing us with breathable and clean air. So, how much oxygen do trees actually produce?

The average human takes in about 550 liters of oxygen in a day — that’s about 145 gallons. Individuals who exercise or are active throughout the day may take in more oxygen on average, depending on the level of activity. 

Some of that oxygen is produced by trees. The amount of oxygen a tree produces is influenced by several factors, including species, age, health, and surroundings. A tree also does not produce the same amount of oxygen year-round.

Typically, old, mature trees produce more oxygen than younger trees. In fact, a mature oak tree can produce, on average, 100,000 liters of oxygen a year. That’s about 274 liters of oxygen a day –– nearly half of what the average human needs.

Douglas fir, beech, spruce, and maple trees are among the tree species that produce the most oxygen. In other words? In addition to the many other vital roles that healthy forests play, it’s in our best interest to be vastly outnumbered by trees.