Oxygen is fundamental to life on Earth. Trees are commonly linked to oxygen production, leading to questions about the exact contribution of Earth’s forests to the planet’s oxygen supply.
How Trees Make Oxygen
Trees generate oxygen through photosynthesis, a biological process taking place primarily in their leaves. This reaction takes place where specialized structures contain chlorophyll. During photosynthesis, trees absorb carbon dioxide from the atmosphere and water from the soil. Light energy from the sun powers the conversion of carbon dioxide and water into glucose, which serves as the tree’s food source. Oxygen is released as a byproduct into the surrounding air.
The Contribution of Forests
Forests release a substantial amount of oxygen into the atmosphere. The quantity of oxygen a single tree produces can vary based on its species, age, and overall health. For instance, a mature oak tree might produce around 100,000 liters of oxygen annually, which is approximately 274 liters per day, representing nearly half of the estimated 550 liters of oxygen an average person consumes daily. One acre of trees can generate enough oxygen to support approximately 18 people for a year. Certain tree species, such as pine, beech, spruce, and maple, are recognized for their higher oxygen production rates.
Earth’s Primary Oxygen Producers
While trees play an important role, the majority of Earth’s atmospheric oxygen originates from microscopic marine organisms known as phytoplankton. These tiny, plant-like organisms drift in aquatic environments, primarily the oceans, and perform photosynthesis, absorbing carbon dioxide and sunlight, and releasing oxygen. Scientists estimate that marine phytoplankton are responsible for producing approximately half of the world’s oxygen. One particular species, Prochlorococcus, a type of cyanobacteria, is remarkably efficient, contributing up to 20% of the oxygen in the entire biosphere. This single bacterium produces more oxygen than all tropical rainforests combined.
The Global Oxygen Balance
Earth’s atmospheric oxygen levels are maintained by a dynamic equilibrium between production and consumption. Photosynthesis, carried out by plants on land and phytoplankton in the oceans, generates oxygen. Oxygen is also consumed by natural processes like respiration (performed by nearly all living organisms including trees themselves), decomposition of organic matter (carried out by bacteria and fungi), and combustion (such as wildfires and the burning of fossil fuels). Mature forests, over their full life cycle, tend to consume nearly as much oxygen as they produce through these processes, resulting in a near-zero net contribution to atmospheric oxygen. The overall atmospheric oxygen concentration reflects this intricate global cycle.