How trees absorb CO2 from the atmosphere: the role of forests and the most effective species in combating the climate crisis

6 minutes

Carbon, in the form of carbon dioxide (CO2), is part of the air we breathe and an indispensable element to ensure life on Earth. For more than a century, however, human activities have increased the concentration of CO2 in the atmosphere, accelerating the climate crisis we are currently experiencing.

Therefore, strategies to remove excess CO2 from the atmosphere are necessary to contain rising temperatures and contribute to the goals of the European Green Deal.

What is meant by CO2 removal?

CO2 removal refers to a range of activities that remove carbon dioxide from the atmosphere by storing it in other natural or artificial elements.

There are various carbon sources on Earth, i.e. processes that release more carbon than they remove. Examples include the use of fossil fuels, such as burning coal to produce electricity and raising livestock for food.

There are also so-called carbon sinks -such as oceans, forests, and agriculture that conversely remove more CO2 than they release: these are our allies in designing CO2 removal strategies.

What are the modes of CO2 removal?

CO2 removal techniques can be either technological or natural. We could summarize the main modes as follows:

  • “Direct Air Carbon Capture and Storage” (DACCS) technologies remove CO2 directly from the atmosphere. Another method of capturing and permanent storage of CO2 is called “Bioenergy with Carbon Capture and Storage” (BECCS), where CO2 is captured and stored from processes in which biomass is converted to fuels or directly burned to generate energy.
  • Nature-based projects: a range of activities that protect, manage and restore ecosystems by maximizing CO2 absorption. An example of nature-based CO2 absorption projects is reforestation activities, which means planting trees where a forest has been destroyed or degraded.

Removing CO2 with trees: do forests remove CO2?

Forests are generally carbon sinks, that is, natural stores that remove more carbon than they release. They are the second largest carbon sink on the planet after the oceans. In fact, forests can sequester CO2 from the atmosphere through photosynthesis by plants, which is then stored in biomass. 

Therefore, forests play a key role in reducing CO2 in the atmosphere and mitigating the climate crisis, so it is necessary to try to increase their CO2 sequestration activity.    

How to improve the CO2 removals of forests

Several actions can be taken to maximize forests’ CO2 removal capacity. First, responsible forest management must be adopted by preventing forest damage caused by natural disturbances such as fire, which would release CO2 stored in plants into the atmosphere, and anthropogenic disturbances such as illegal logging.

Another strategy is to increase the area covered by forests by reforesting previously forested or other degraded areas. This strategy sometimes runs against the limits dictated by land availability: agriculture and urban expansion compete for and consume increasing amounts of land, often resulting in deforestation

By contrast, a lesser-known but equally relevant strategy is to use wood-based materials in construction. These materials store CO2 over the long term by replacing iron and concrete materials that emit high amounts of CO2.

However, forests alone cannot solve the climate crisis. In fact, it has been estimated that to offset a single year of global CO2 emissions, an area larger than Germany, France, and Spain combined would have to be reforested or afforested and allowed to grow. 

Forests are thus a valuable tool to achieve climate goals, but more is needed: combining CO2 removal activities with emission reduction activities is essential.

How do you calculate how much CO2 a tree absorbs?

Several methodologies exist for quantifying the CO2 absorbed by a tree. Typically, conversion factors of the annual rate of increase of woody biomass in the tree to CO2 equivalent are used. 

The rate of increase can vary depending on the species and site-specific conditions, such as soil fertility, climate, plant age, and other factors. It is estimated based on forest measurements, in which tree sizes, such as diameter and height, are monitored.

In offset projects, to quantify improved interventions’ impact on CO2 sequestration, the post-intervention situation is usually compared with the initial situation, which is set as a baseline. In other words, at the beginning of the project, the amount of CO2 stored in the forest before the interventions is calculated. A few years later, the same trees are returned to the forest, the measurements are measured, compared with the baseline, and the amount of growth the tree has grown over the period is calculated. Based on this, the equivalent CO2 absorbed is estimated.

Which trees are best at absorbing CO2?

Determining which trees have the highest CO2 absorption potential is difficult. Many sources report different data intact. Many factors influence this capacity, including the species and age of the tree, the need for maintenance work, and the climate in which the tree is located.

In general, species characterized by faster growth also absorb CO2 faster. In the long term, however, the species that absorb the most CO2 can reach the most significant size or live the longest.

Among the best species in CO2 absorption are tropical species, such as:

  • Teak, which has the highest carbon sequestration capacity among trees in India
  • Mangroves sequester much CO2 from the atmosphere and offer numerous other benefits in combating climate change.
  • Species belonging to the genus Eucalyptus and Acacia grow very fast, especially in their early years.

However, pines and oaks stand out in more temperate settings for their absorptive capacity. Evergreen species such as Pinus ponderosa and Spanish Pinus occidentalis are among the most effective CO2 storehouses due to their fast growth and large size. Among deciduous species, on the other hand, oaks stand out for their high absorption capacity, thanks to their large canopies and dense wood.

How many kilograms of CO2 does a tree absorb in a year?  

We can state to a certain degree of approximation that in a natural context, the CO2 absorption potential of a tree averages between 20 and over 50 kgCO2/year over an average time range of 20 to over 30 years.

What we do for CO2 absorption (and what a company can do)

At Etifor, we created the WOWnature platform, which enables forest owners, citizens and businesses to do their part in combating climate change by helping us reforest degraded land and protect existing forests. To date, we have planted more than 250,000 trees and improved the management of more than 140 forests, absorbing about 119,023,643 kg/CO2.