Trees absorb carbon dioxide (CO2) from the atmosphere through the process of photosynthesis. Throughout this biochemical process, chlorophyll in the tree's leaves harnesses sunlight to convert CO2 and water into glucose and oxygen. While glucose serves as a source of energy for the tree, oxygen is released into the atmosphere as a byproduct. Trees store carbon in the form of biomass, encompassing roots, stems, branches, and leaves. Throughout their lifespan, trees continue to sequester carbon, acting as long-term storage units for atmospheric CO. Sustainable forest management, afforestration, reforestation and proforestation are therefore important contributions to climate change mitigation. Afforestation is the establishment of a forest in an area where there was no previous tree cover. Proforestation is the practice of growing an existing forest intact toward its full ecological potential. An important consideration in such efforts is that the carbon sink potential of forests will saturate and forests can turn from sinks to carbon sources. The Intergovernmental Panel on Climate Change (IPCC) concluded that a combination of measures aimed at increasing forest carbon stocks, and sustainable timber offtake will generate the largest carbon sequestration benefit.
In terms of carbon retention on forest land, it is better to avoid deforestation than to remove trees and subsequently reforest, as deforestation leads to irreversible effects e.g. biodiversity loss and soil degradation. Additionally, the effects of af- or reforestation will be farther in the future compared to keeping existing forests intact. It takes much longer − several decades − for reforested areas to return to the same carbon sequestration levels found in mature tropical forests.
There are four primary ways in which reforestation and reducing deforestation can increase carbon sequestration. First, by increasing the volume of existing forest. Second, by increasing the carbon density of existing forests at a stand and landscape scale. Third, by expanding the use of forest products that will sustainably replace fossil-fuel emissions. Fourth, by reducing carbon emissions that are caused from deforestation and degradation.
The planting of trees on marginal crop and pasture lands helps to incorporate carbon from atmospheric  into biomass. For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die. To this end, land allotted to the trees must not be converted to other uses and management of the frequency of disturbances might be necessary in order to avoid extreme events. Alternatively, the wood from them must itself be sequestered, e.g., via biochar, bio-energy with carbon storage (BECS), landfill or stored by use in construction. 
Reforestation with long-lived trees (>100 years) will sequester carbon for substantial periods and be released gradually, minimizing carbon's climate impact during the 21st century. Earth offers enough room to plant an additional 1.2 trillion trees. Planting and protecting them would offset some 10 years of CO emissions and sequester 205 billion tons of carbon. This approach is supported by the Trillion Tree Campaign. Restoring all degraded forests world-wide would capture about 205 billion tons of carbon in total, which is about two-thirds of all carbon emissions.
Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.
During a 30-year period to 2050 if all new construction globally utilized 90% wood products, largely via adoption of mass timber in low rise construction, this could sequester 700 million net tons of carbon per year, thus negating approximately 2% of annual carbon emissions as of 2019. This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.
As enforcement of forest protection may not sufficiently address the drivers behind deforestation – the largest of which being the production of beef in the case of the Amazon rainforest – it may also need policies. These could effectively ban and/or progressively discourage deforestation-associated trade via e.g. product information requirements, satellite monitoring like the Global Forest Watch, related eco-tariffs, and product certifications.