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Afforestation and Reforestation

Women with seedlings for reforestation in Tanzania. Image copyrights: USAID Africa Bureau - Uploaded by Elitre, Public Domain, https://commons.wikimedia.org/w/index.php?curid=21460185
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Deforestation is abundant around the world, especially in rich tropical forests such as the Amazon. Massive deforestation is carried out in pursuit of industrialization and development goals. Given this reality and the urgency of climate change, large-scale afforestation, reforestation, and proforestation are among critical negative emissions strategies. Afforestation refers to the planting of trees in areas that forests have not existed in recent history (they may have been previously converted for agriculture, mining, or other purposes). Reforestation refers to the replanting of trees in recently cleared forested lands. And proforestation refers to the practice of intentionally letting middle-aged and mature forests grow. Plants and trees are natural carbon sinks. Afforestation, reforestation, and proforestation work on the principle of carbon dioxide sequestration to aid plant and tree growth.

Afforestation/reforestation (AR) is not technologically demanding and relies on well-established principles allowing for immediate and easy deployment. Global estimates for sequestration through AR ranges from 0.73 to 5.5 Gt CO2/ year. Most estimates place the cost of sequestration through AR between 10 and 50 $/tCO2 (Minx et al, 2018). However, to achieve this level of sequestration, a large amount of land would have to be reclaimed or reforested, with estimates ranging from 320 to 970 million hectares (790 to 2400 million acres) of new forested land. 

Such massive AR would present challenges such as large nutrient requirements. Excessive application of fertilizers could pose the risk of nutrient runoffs and additional  emissions of greenhouse gas nitrogen oxides (with 300x the global warming potential of carbon dioxide). AR could run into political roadblocks as the continued storage of carbon could be disrupted through decisions to clear-cut forests in favor of other land use activities such as farming. The potential could be further limited depending on the fertility of reclaimed soil which could be significantly lowered owing to multiple cycles of deforestation or intensive cultivation.

Despite these challenges, afforestation and reforestation are integral to negative emission strategies that would be required to meet climate goals.