Planting Trees as a Nature-Based Solution to Mitigate Climate Change: Opportunities, Limits, and Trade-Offs

Trees and forests are nature-based solutions of strategic importance for climate change mitigation. Policy and popular media are focused on the number of trees to plant, but that cannot be a definitive solution. A growing number of scientific papers address the problems concerning tree plantations and forest restoration for climatic purposes. In this review, we analyze ecological limitations and trade-offs to be considered for the realization and management of these interventions. Terrestrial sinks (forests and other terrestrial natural ecosystems) can absorb only a fraction of the carbon emitted, and the establishment of new effective forests is constrained by ecological limitations. Moreover, the stimulation of tree growth due to carbon fertilization is offset by the harshening of ecological conditions due to climate change (higher temperatures beyond the optimum for photosynthesis, increasing drought, and nutritional imbalances). The increase in frequency and severity of disturbances can turn forests from sinks to sources of carbon. Finally, physiological mechanisms connected to albedo and the emission of organic volatile compounds (VOCs) reduce the efficacy of climate cooling. Although such constraints exist, the establishment of new plantations and the restoration of existing forests are still necessary but are just one of the actions to fight climate change and must not be seen as an alternative to reducing carbon emissions. Considering limitations and trade-offs in the models to estimate tree growth and carbon storage will allow us to produce more realistic plans for climate mitigation.