Planting trees for carbon credits: a discussion of context, issues, feasibility, and environmental benefits

Increasing concentrations of certain atmospheric gases, particularly CO 2 , may be intensifying Earth's naturally occurring greenhouse effect. Anthropogenic emissions of CO 2 are mostly associated with fossil-fuel combustion and deforestation, both of which are intimately associated with diverse economically important activities. This circumstance will make it difficult for society to rapidly achieve large reductions in the emissions of CO 2 . The extensive planting of trees can contribute to offsetting a portion of the anthropogenic emissions of CO 2 and other radiatively active gases (RAGs). Growing plants fix atmospheric CO 2 into organic carbon of their accumulating biomass, and ecological budgets suggest that substantial carbon credits can be achieved by planting large numbers of trees, in both urban and rural environments. Moreover, many additional noncarbon environmental benefits are achieved by planting trees over extensive areas. A tree-planting strategy could not, however, be practically used to offset more than a relatively small portion of the RAGs emitted through human activities. This limitation is mostly due to the immense areas of land that would have to be afforested to achieve more substantial offsets. Ultimately, effectively dealing with an anthropogenic enhancement of Earth's greenhouse effect will require a comprehensive integrated strategy, the major component of which will be reduced emissions. However, carbon offsets associated with the planting of trees will also be an important element of that integrated strategy. This review discusses issues involved in the planting of trees to offset emissions of CO 2 and other RAGs. Forest-carbon offsets are discussed in the contexts of the greenhouse effect and climate change, options for reducing emissions of CO 2 , and the feasibility and environmental benefits of achieving CO 2 offsets by extensively planting trees. Attention is paid to both carbon and noncarbon benefits, in the contexts of industrial and nonindustrial forests, both urban and rural.